Azygos venous system
Fourth
Common lumbar vein
Azygos vein iliac vein Iliolumbar vein
The azygos vein has a variable origin from the azygos lumbar vein or
from the posterior aspect of the inferior vena cava at or below the level External
of the renal veins (Figs 56.2–56.3; see Fig. 56.14B). When present, the iliac vein
azygos lumbar vein ascends anterior to the upper lumbar vertebral
bodies and passes either posterior to or through the right diaphragmatic
crus or traverses the aortic hiatus to the right of the cisterna chyli. Ante- Internal iliac vein Median sacral vein
rior to the twelfth thoracic vertebra, it is joined by a venous trunk,
Fig. 56.3 The most common topography of the azygos venous system.
formed by the union of the right ascending lumbar and subcostal veins,
to form the azygos vein. In the absence of a lumbar azygos vein, this
common trunk may continue as the azygos vein proper. The azygos vein In its course, the azygos vein lies anterior to the bodies of the lower
passes to the right, posterior to the right crus of the diaphragm, and eight thoracic vertebrae, anterior longitudinal ligament and right pos-
ascends in the posterior mediastinum to the level of the fourth thoracic terior intercostal arteries. Right lateral relations are the right sympa-
vertebra, where it arches anteriorly, superior to the right pulmonary thetic chain, the right greater splanchnic nerve, lung and pleura. Left
hilum, and joins the posterior aspect of the superior vena cava, just lateral relations are the thoracic duct, aorta and, where the vein arches
superior to its pericardial incorporation. anteriorly, the oesophagus, trachea and right vagus. Aortic pulsations


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may assist venous return in the azygos and hemiazygos veins, although Table 56.1 Classification of regional mediastinal lymph nodes into regional lymph
only a small and variable number of imperfect valves are present. Infe- node stations
riorly, the azygos vein lies posterior to the oesophagus, from which it
Station Description
is separated by a pleural recess, the azygo-oesophageal recess. There are
differences in the appearance of the contour of this recess on computed 1 The highest mediastinal nodes lying above a horizontal line, at which level
the left brachiocephalic vein crosses the trachea
tomography (CT) between children and adults. The recess is dextrocon-
vex below the age of 6 years, non-concave (equally divided between 2 Upper paratracheal nodes lying below the line of the highest mediastinal
nodes and above a line drawn horizontally at the level of the upper border of
straight and convex) between 6 and 12 years and concave, as in adults,
the aortic arch
after the age of 12 years (Miller et al 1993). Its major tributaries are the
3 Prevascular and retrotracheal nodes lying behind the trachea but in front of
right intercostal veins (the first drains into the right brachiocephalic the great vessels
vein and the second, third and fourth form a common trunk, the supe-
4 Lower paratracheal nodes lying below the upper margin of the aortic arch
rior intercostal vein), the right ascending lumbar and subcostal veins, and down to the upper margin of the corresponding upper lobe bronchus. On
mediastinal, oesophageal, pericardial and right bronchial veins, and the the right side, this is the upper margin of the right upper lobe bronchus; the
hemiazygos and accessory hemiazygos veins. majority of nodes in this area tend to be positioned anterolateral to the
trachea. On the left side, the nodes are located below the upper margin of
Numerous anastomoses exist between the tributaries and the main
the aortic arch and above the margin of the left upper lobe bronchus. They


trunks of the azygos, hemiazygos and accessory hemiazygos veins, the
lie to the right of the ligamentum arteriosum, between the ligament and the
inferior vena cava and the vertebral venous plexuses. These allow for trachea
alternate drainage pathways in case of segmental agenesis (‘interrup- 5 Subaortic nodes lying in the aortopulmonary window and situated to the right
tion’) or thrombosis of the inferior vena cava (see also below for the of the ligamentum arteriosum, aorta or left pulmonary artery, but proximal to
variations of the azygos vein). the first division of the left pulmonary artery
6 Para-aortic nodes lying between the upper margin of the aortic arch and
Hemiazygos vein lateral to the ascending aorta and aortic arch
The hemiazygos vein represents the left-sided equivalent of the more 7 Subcarinal nodes are not associated with the lower lobe bronchi
inferior part of the azygos vein. It originates in a similar fashion (from 8 Para-oesophageal nodes lie well below the subcarinal nodes, close to the
the union of the left lumbar ascending and subcostal veins) but exhibits pulmonary veins
more variability; it may also connect with the left renal vein via the 9 Nodes lying within the pulmonary ligament
equivalent of the lumbar azygos vein. The hemiazygos vein crosses 10, 11 and 12 Designated the hilar, interlobar and lobar nodes, respectively
posterior to the aorta and oesophagus, and either anterior or posterior
to the thoracic duct, and usually terminates in the azygos vein at the
level of the eighth thoracic vertebra (see Fig. 56.2). It receives the lower
three left posterior intercostal, mediastinal and oesophageal veins. Oesophagus, cervical part Thyroid gland, right lobe
Accessory hemiazygos vein Common carotid artery
The accessory hemiazygos vein functions as the left-sided mirror image
Brachiocephalic
of the superior portion of the azygos vein. It drains the fifth to eighth Subclavian artery trunk
posterior intercostal veins and occasionally the left bronchial veins, and
Subclavian artery
usually terminates in the azygos vein after crossing the seventh thoracic
Juxta-oesophageal nodes Superior vena cava


vertebra. The first posterior intercostal vein drains directly into the left
brachiocephalic vein, while the second to the fourth drain indirectly to Aortic arch Trachea
the accessory hemiazygos vein via the left superior intercostal vein. The Inferior tracheobronchial
accessory hemiazygos vein may also join the hemiazygos vein. One or nodes Superior
more prevertebral transversal anastomoses may be present. tracheobronchial nodes
Variations of the azygos venous system Left superior pulmonary Azygos vein
vein
The origin, course, tributaries, anastomoses and termination of the
Superior tracheobronchial
azygos system of veins are all highly variable. The arrangement shown
nodes
in Figure 56.2 represents the most common pattern with a right-
Superior
sided azygos vein. The left channel may be absent or underdeveloped, Left pulmonary
tracheobronchial
allowing direct drainage of the left intercostal veins into the azygos artery
nodes
and/or the termination of the accessory hemiazygos into the left
Right
brachiocephalic vein. In such cases, the azygos vein is in median pulmonary
position. Left inferior pulmonary artery
vein
Internal thoracic arteries and veins
Posterior mediastinal
nodes Right inferior
The internal thoracic vessels are described on pages 942 and 943. pulmonary vein
Oesophagus, Posterior mediastinal
Pulmonary arteries and veins thoracic part nodes
The pulmonary vessels are described on pages 959 and 960.
Inferior vena
Posterior intercostal arteries and veins cava
The posterior intercostal veins accompany their arteries in eleven pairs;
they are described on page 944.
Mediastinal lymph nodes
For the purposes of staging lung cancer, thoracic surgeons classify the Fig. 56.4 The general disposition of the thoracic lymph nodes, posterior
aspect. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas
mediastinal lymph nodes into regional lymph node stations, which are
of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
defined as shown in Table 56.1 and Figure 56.4.
These groups are not sharply demarcated. Pulmonary nodes become


continuous with the bronchopulmonary nodes, and these, in turn,
merge with the inferior and superior tracheobronchial nodes, which are nal and brachiocephalic nodes as the right and left bronchomediastinal
continuous with the paratracheal group. The tracheobronchial nodes trunks. The right trunk may occasionally join a right lymphatic duct or
drain the lungs, bronchi, the thoracic part of the trachea, and heart, and another right-sided lymph trunk, and the left trunk may join the tho-
also receive efferents from the posterior mediastinal nodes. Their effer- racic duct, but usually they open independently in or near the ipsilateral
ent vessels ascend on the trachea to unite with efferents of the paraster- jugulosubclavian junction (see Fig. 29.16).


Mediastinum
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In congenital interruption of the inferior vena cava or acquired
thrombosis, the azygos system provides an alternative pathway for
venous drainage. A higher than usual azygos arch may travel within an
accessory azygos fissure (four pleural layers) and isolate a portion of
the right upper lobe of the lung medially: the ‘azygos lobe’, which may
rarely be radiopaque on a chest radiograph. An azygos lobe is rarely
present and is rarely seen on chest radiographs. The azygos fissure often
presents a nestled azygos vein as a lung ‘pseudo-nodule’ on a chest
radiograph; it is typically comma-shaped and should not to be confused
with a more rounded early lung carcinoma or metastasis.
Metastatic involvement of these lymph nodes has important prog-
nostic implications and influences the choice of treatment (Mountain
and Dresler 1997). The staging system for lung cancer classifies involve-
ment of ipsilateral hilar lymph nodes as N1, ipsilateral mediastinal
lymph nodes as N2, contralateral mediastinal or hilar nodes as N3 and
supraclavicular/scalene nodes as M1 (distant metastases).


Right lymphatic trunk
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Mediastinoscopy 3 or 4 cm superior to the clavicle, crossing anterior to the vertebral
vessels, the left sympathetic trunk, the vertebral ganglion, the thyro-
The decision to proceed with mediastinoscopic biopsy depends on
cervical trunk and the left phrenic nerve.
whether suitable nodal stations seem involved on CT scanning and
In some patients, two thoracic ducts exist within the mediastinum,
whether there is a history of prior neck and mediastinal surgical
and occasionally a single thoracic duct may empty into right-
procedures.
sided venous structures, the latter disposition being more frequent in
individuals with an aberrant right subclavian artery (the latter origi-
THORACIC DUCT nating from the distal aortic arch ascending posterior to the
oesophagus).
When present as a single channel, the thoracic duct is 5 mm in
The thoracic duct conveys the lymph from the entire body, except the
diameter at its origin, narrows to 2–3 mm at mid-thoracic level and
right part of the head, neck and heart, right upper limb, right lung and
then widens again at its termination. Alternatively, it may divide into
part of the convex surface of the liver, back to the venous circulation.
two or three branches that eventually reunite or drain into both the left
It usually originates anterior to the first or second lumbar vertebrae,
and right venous systems. The duct appears sinuous and has valves
where the intestinal and two lumbar lymph trunks join to form the
throughout its length; a bicuspid valve at its termination may prevent
cisterna chyli. (Both the thoracic duct and the cisterna chyli are variable
the backflow of blood. As it passes through the mediastinum, the tho-
in their origin, course and length; the latter is even more variable in
racic duct also receives non-chylous lymph from tributaries that drain
width and shape than the thoracic duct.) From the superior aspect of
regions of the pulmonary parenchyma and parietal pleura. The sum of
the cisterna chyli, the thoracic duct passes through the aortic hiatus and
these sources accounts for a total lymphatic flow through the thoracic


enters the posterior mediastinum, lying to the right between the aorta
duct of 1500–2400 ml per day in proportion to the dietary intake of
and the azygos vein up to the level of the fifth thoracic vertebra, where
fat, particularly long-chain triglycerides.
it typically crosses over the vertebral column posterior to the oesopha-
The anatomy of the thoracic duct determines the location of the
gus (see Fig. 56.7B). It continues upwards, first posterior to the aortic
effusion seen with duct injury or obstruction.
arch adjacent to the left side of the oesophagus, then posterior to the
left subclavian artery in the superior mediastinum. It next arches over Tributaries of the thoracic duct
the subclavian artery and descends anteriorly to empty into the venous
Some tributaries of the thoracic duct may terminate directly in the
circulation in the region of the left jugular and subclavian veins, either
venous system. Numerous anastomoses exist between visceral, parietal,
at their very confluence or in proximity, sometimes in the left brachio-
limb and mammary lymphatics, an arrangement that is manifest in
cephalic vein (Fig. 56.5, p. 462). In the space between longus colli, the
observed multiple patterns of dissemination of cancer cells. Besides the
anterior scalene muscles and the pleural dome, the duct usually arches
cisterna chyli and its tributaries, bilateral ascending lumbar lymph
trunks from the upper lateral aortic nodes pierce the corresponding
diaphragmatic crus and eventually join the thoracic duct in the poste-
Right lymphatic duct Oesophagus Thoracic duct rior mediastinum. The inferior six or seven intercostal lymph trunks
Jugular from the corresponding bilateral intercostal nodes descend to terminate
lymph trunk in the duct, either directly or by variable common trunks. The left upper
intercostal lymphatics may join the cervical portion of the duct or the
Right broncho- Subclavian
mediastinal trunk lymph trunks subclavian trunk. The left subclavian trunk usually joins the thoracic
duct but may open independently into the left subclavian vein. These
mediastinal trunks provide lymph drainage paths to the thoracic duct


Brachiocephalic from the convex diaphragmatic aspect of the liver, the diaphragm, the
Superior vena vein pericardium, heart and oesophagus, and many possess terminal bicus-
cava pid valves. The left bronchomediastinal trunk occasionally joins the
thoracic duct but usually has an independent venous termination. The
left jugular trunk usually joins the thoracic duct but may open inde-
pendently into the left internal jugular vein.
Azygos vein Accessory
Injury during oesophageal surgery
hemiazygos
vein The variable origin, course and length of the thoracic duct, coupled with
failure to identify it at surgery, may lead to its inadvertent incision or
Intercostal
lymph nodes transection, particularly during trans-hiatal and thoracoscopic oesopha-
geal surgery, with an incidence between 0.2 and 3% (Wemyss-Holden
et al 2001). Thoracic duct laceration is a potentially life-threatening
complication; mortality rates are higher with conservative management
but still elevated even after surgical ligation. Rupture of the thoracic
duct leads to leakage of chyle, which is rich in lipid, protein, T lym-
phocytes (ranging from 400 to 6800 cells/µl), immunoglobulins and
fat-soluble vitamins, and hence a progressive nutritional and immune
deficit develops. Postoperative chylous effusions are usually the result
of damage to ductal tributaries rather than to the duct itself, and are
usually self-limiting. The greater incidence of injury with trans-hiatal
Thoracic duct Hemiazygos vein
resection may be attributable to shear forces during the mobilization
of the distal oesophagus, whereas the limited field of view probably
contributes to the greater incidence of thoracic duct injury during tho-
racoscopic surgery. Injury should be suspected in the postoperative
period if there is either an enlarging mediastinal silhouette on serial
Cisterna chyli chest radiographs or a significant milky drainage from the chest or
Confluence of abdominal drains. An electrophoretic confirmation of the presence of
lymph trunks chylomicrons in the pleural fluid is diagnostic, amongst other tests. The
thoracic duct may be injured during the left cervical approach for the
exposure of the vertebral and subclavian arteries or the cervicothoracic


Lateral aortic (stellate) sympathetic ganglion. However, deliberate ligature of the duct
lymph nodes at this level represents an accepted surgical manœuvre with no particu-
lar consequences.
Retro-aortic
lymph nodes
RIGHT LYMPHATIC TRUNK
Fig. 56.5 The thoracic and right lymphatic ducts. Note that the accessory
hemiazygos vein is crossing the median plane lower and the hemiazygos The right lymphatic trunk has an inconstant anatomy (see Fig.
higher than typically found. 56.5). Its three main tributaries – the right jugular, subclavian and


Mediastinum
979.e1
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RETPAHC
Mediastinoscopy can be performed with video-assisted or direct
optic visualization. A transverse incision is made in the suprasternal
notch through the deep lamina of the deep cervical fascia after retrac-
tion of sternohyoid and sternothyroid within its superficial lamina. The
pretracheal plane is dissected and a space is created between the anterior
aspect of the trachea and the brachiocephalic trunk inferior to the carina
and along both sides of the trachea and main bronchi. This space
facilitates biopsy of the upper paratracheal 2R/L stations, the right para-
tracheal 4R station and higher nodes from the left paratracheal 4L
station superior to the aortic arch. Anterior subcarinal station 7 and
bilateral hilar stations 10R/L may be accessible but are technically chal-
lenging. Nodes can be sampled or removed entirely for histological
evaluation.
The anterior part of the superior mediastinum is more difficult to
assess by mediastinoscopy and usually requires an anterior mediastin-
otomy (Chamberlain procedure). This is performed to biopsy nodes
from the more inferior aspect of the left paratracheal 4L station, sub-
aortic station 5, para-aortic station 6 and subcarinal station 7, and also
facilitates anterior mediastinal mass biopsy.
Complications of mediastinoscopy include haemorrhage, injury to
the trachea or left recurrent laryngeal nerve, and pneumothorax.
Endobronchial ultrasound can be performed to biopsy lymph nodes
in stations 1–4, 7 and 10–12, using fine needle aspiration through the
tracheal or bronchial walls. In a similar way, transoesophageal ultra-
sound may biopsy subcarinal station 7, para-oesophageal station 8 and
pulmonary ligament station 9 nodes.
Because the thoracic duct crosses the mediastinum at, or at about,
the level of the fifth thoracic vertebral body, lymphatic injury or obstruc-
tion above or below this level results in a left- or right-sided pleural
effusion, respectively (Doerr et al 2001). Anomalies and sites of injury


to the duct are identified by lymphangiography, with or without post-
procedure CT scanning, or lymphoscintigraphy. Lymphangiography is
performed using bilateral localization of pedal lymphatics with a sub-
cutaneous injection of methylene blue, followed by a minor surgical
procedure to cannulate the lymphatic vessel, and injection of Lipiodol
contrast agent. Conventional plain films and CT images (without intra-
venous contrast) are then obtained. Lymphangiography can identify
areas of chyle leakage and lymphangiectasia in the majority of patients
(Deso et al 2012).


MEdiASTinuM
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bronchomediastinal trunks – often terminate separately at the jugular or through the diaphragmatic crus to become the lumbar sympathetic
and subclavian veins (see Fig. 29.16). In up to one-fifth of individuals, trunk.
they may aggregate to form the right lymphatic trunk, usually 0.5–1 cm The ganglia are small and interconnected by intervening segments
in length. The terminal portions of the right lymphatic trunk and of the of the trunk. Unlike other mammalian species, including primates, each
thoracic duct are concealed by the scalene fat pad, which renders them sympathetic ganglion in humans is connected to two consecutive spinal
more vulnerable during surgery. nerves: the corresponding and succeeding nerves. The classic descrip-
tion is that two or more rami communicantes, named white (myelin-
ated, preganglionic) and grey (unmyelinated, postganglionic), connect
AUTONOMIC NERVOUS SYSTEM
each ganglion with its corresponding spinal nerve, the white rami
joining the nerve distal to the grey.
The thoracic autonomic nervous system consists of the right and left Variation in this pattern is common, especially at the upper thoracic
ganglionated sympathetic chains and vagi, and the cardiac, pulmonary levels, but symmetry is rarely seen. Additional ascending and descend-
and oesophageal plexuses. The cardiac plexus is described on page 1021, ing rami issue from the second (54% and 46%, respectively), third (6%
the pulmonary plexus on page 961, and the oesophageal plexus is and 25%) and fourth ganglia (5% and 8%) (Cho 2005). Occasionally,
described below. a grey and a white ramus fuse to form a ‘mixed’ ramus. An inconstant
intrathoracic ramus may join the second intercostal nerve to the ventral
ramus of the first thoracic nerve proximal to the point where the latter
THORACIC SYMPATHETIC TRUNK issues a large branch to the brachial plexus (Kuntz 1927). This intrathor-
acic nerve of Kuntz is considered to carry sympathetic fibres to the
The thoracic sympathetic trunk contains ganglia that are almost equal brachial plexus without passing through the sympathetic trunk and has


in number to those of the thoracic spinal nerves (usually 11, occasion- been held responsible for the recurrence of symptoms following sym-
ally 12, rarely 10 or 13) (Figs 56.6–56.7). Almost always, the first pathectomy. The anatomical variation exhibited by the communicating
thoracic ganglion is fused with the inferior cervical ganglion, forming rami and the location of the second sympathetic ganglion may also
the cervicothoracic (stellate) ganglion; occasionally, the second thoracic contribute to surgical failure and symptom recurrence.
ganglion is included in this fusion. The succeeding ganglia are counted The medial branches from the upper five ganglia are very small, and
in order to make them correspond numerically with the correlative may supply filaments in a retrograde manner to the thoracic aorta and
segmental structures. Except for the second and lowest two or three, the its branches, as they pass to the cardiac plexuses (Kawashima 2011).
thoracic ganglia lie against the costal heads, posterior to the costal Some fibres form a fine thoracic aortic plexus with filaments from the
pleura. The second thoracic sympathetic ganglion is commonly located greater splanchnic and vagus nerves. Rami of the second to fifth or
in the second intercostal space, and the lowest two or three ganglia lie sixth ganglia enter the posterior pulmonary plexus. Small branches of
lateral to the bodies of the corresponding vertebrae. Inferiorly, the tho- these pulmonary and cardiac nerves pass to the oesophagus and
racic sympathetic trunk passes posterior to the medial arcuate ligament trachea.
Common carotid artery Cervicothoracic ganglion (stellate ganglion) Fig. 56.6 The thoracic autonomic
nervous system. (With permission
Vagus nerve
Trachea from Waschke J, Paulsen F (eds),
Sympathetic trunk, middle cervical ganglion Recurrent laryngeal nerve Sobotta Atlas of Human Anatomy,
Scalenus anterior 15th ed, Elsevier, Urban & Fischer.
Subclavian artery
Copyright 2013.)
Ansa subclavia
Ansa subclavia
Subclavian artery
Vagus nerve
Sympathetic trunk,
Thoracic aortic plexus,
second thoracic ganglion
cardiac plexus
Vagus nerve


Vagus nerve,
Recurrent laryngeal nerve
bronchial branches
Ascending aorta
Intercostal nerves
Right main bronchus
Thoracic aorta
Sympathetic trunk,
Vagus nerve,
thoracic ganglia
oesophageal plexus
Greater splanchnic
nerve
Lesser splanchnic
nerve Sympathetic trunk
Diaphragm
Oesophagus,
abdominal part
Anterior vagal
Duodenum trunk, anterior
gastric branches
Subcostal nerve
Abdominal aorta


Autonomic nervous system
981
65
RETPAHC
A
Brachial plexus, infraclavicular part Subclavian artery
Sympathetic trunk, second thoracic ganglion Clavicle
Vagus nerve, recurrent laryngeal nerve Subclavius
Vagus nerve, thoracic cardiac branches Scalenus anterior
Vagus nerve, pulmonary plexus
Subclavian vein
Azygos vein
Internal thoracic artery
Right main bronchus
Phrenic nerve
Right brachiocephalic vein
Bronchial vein
Pericardiacophrenic artery
Vagus nerve, and vein
thoracic cardiac branches
Thymus
Superior vena cava
Posterior intercostal vein
Pulmonary arteries
Phrenic nerve;
pericardiacophrenic
artery and vein
Pulmonary veins
Fibrous pericardium;
Greater splanchnic parietal pleura,
nerve mediastinal part
Pulmonary ligament
Posterior intercostal
arteries
Vagus nerve,
oesophageal plexus
Parietal pleura,
costal part
Oesophagus
Fig. 56.7 The mediastinum. A, Right lateral aspect. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed,
Elsevier, Urban & Fischer. Copyright 2013.) Continued
The larger medial branches from the lower seven ganglia supply the Thoracic sympathectomy
aorta and then unite to form the greater, lesser and least splanchnic
nerves (see below for variability).
Endoscopic thoracic sympathectomy (ETS) is a surgical procedure used
The greater splanchnic nerve consists mainly of myelinated pregan-
to relieve the symptoms of craniofacial, palmar or axillary hyperhidro-
glionic efferent and visceral afferent fibres, and is formed by branches
sis, facial blushing, Raynaud’s disease with digital ulcers, and reflex
from the fifth to ninth or tenth thoracic ganglia; fibres in the upper
sympathetic dystrophy (shoulder–hand syndrome).
branches may be traced to the first or second thoracic ganglia. Its roots
vary from one to eight, four being the most usual number. It descends
obliquely on the vertebral bodies, supplies branches to the descending


thoracic aorta, and perforates the ipsilateral diaphragmatic crus to VAGUS NERVE IN THE MEDIASTINUM
end mainly in the coeliac but partly in the aorticorenal ganglion and
suprarenal (adrenal) gland. A splanchnic ganglion exists on the nerve The vagus nerve contains preganglionic parasympathetic fibres that arise
opposite the eleventh or twelfth thoracic vertebra in a majority of in its dorsal nucleus and travel in the nerve and in its pulmonary,
individuals. cardiac, oesophageal, gastric and intestinal branches (see Fig. 56.6).
The lesser splanchnic nerve, formed by rami of the ninth and tenth Vagal fibres that originate from neurones in the nucleus ambiguus are
(sometimes the tenth and eleventh) thoracic ganglia and the trunk distributed to the constrictor muscles of the pharynx and the intrinsic
between them, pierces the diaphragm with the greater splanchnic nerve muscles of the larynx. The proportion of efferent parasympathetic fibres
and joins the aorticorenal ganglion. in the vagus varies at different levels but is small relative to its sensory
The lowest (least) splanchnic nerve (or renal nerve) from the lowest and sensorimotor content. Efferent fibres relay in minute ganglia in the
thoracic ganglion enters the abdomen with the sympathetic trunk to visceral walls.
end in the renal plexus. Cardiac branches join the cardiac plexuses and relay in ganglia that
The greater splanchnic nerve is always present, the lesser is usually are distributed freely over both atria in the subepicardial tissue. The
present, and the least is often absent. A fourth (accessory) splanchnic terminal fibres are distributed to the atria and the atrioventricular
nerve has been described. bundle; they are concentrated around the sinu-atrial and, to a lesser


Mediastinum
981.e1
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RETPAHC
ETS may be beneficial to ameliorate cerebral vascularization in
patients with moyamoya disease and to treat migraine, hyperactive
bronchial states, long QT syndrome, causalgic pain, erythromelalgia,
Buerger’s disease, Prinzmetal’s angina, and chronic non-infectious rhin-
itis. ETS is also effective in frostbite injury, especially if performed
within 36–72 hours of cold exposure.
The operation involves making tiny incisions posterior to the pecto-
ral fold in the axilla, and insufflating a small amount of carbon dioxide
into the thoracic cavity to allow access with a modified thoracoscope.
In the treatment of facial blushing, it is sufficient to divide the fibres
that run superiorly from the second thoracic ganglion over the neck of
the second rib, leaving the second ganglion almost intact. Treatment of
palmar hyperhidrosis requires ablation thermocoagulation of the sym-
pathetic trunk over the necks of the third and fourth ribs, taking care
to avoid any spreading of thermal energy along the trunk in order to
avoid damaging the more superior stellate ganglion (see ‘Horner’s syn-
drome’ below). The risk of compensatory sweating is greatly reduced,
though not completely excluded, by limiting the number of ganglia
treated to an absolute minimum. As an additional procedure, dividing
the inconstant sympathetic pathways (nerve of Kuntz, ascending or
descending additional rami communicantes) on the second, third and
fourth ribs may improve surgical outcomes.
The effect is immediately evident: the patient awakes from anaesthe-
sia with dry, warm hands. In many cases, even hyperhidrosis of the feet
improves, but the underlying anatomical/physiological mechanisms are
not yet properly understood (Gofeld and Faclier 2006). Surgical com-
plications are very rare; Horner’s syndrome is the most feared, and is
caused by damage to the stellate ganglion and interruption of the sym-
pathetic fibres from C8–T1, which ascend around the arteries supplying
the head and neck (see pp. 468, 469 and Fig. 29.18). Side-effects
include compensatory sweating (ranging from barely noticeable to
quite disturbing) in other locations of the body on exercise or from


exposure to high temperatures in up to 70% of patients. Severe in 5%
of patients, it may be more frequent in those with axillary hyperhidrosis
(when two more inferior ganglia have to be divided); some surgeons
do not now consider isolated axillary hyperhidrosis as an indication for
this procedure. Gustatory or olfactory sweating may also occur in up to
one-third of patients but is rarely considered a problem. Other docu-
mented side-effects are the inability to raise the heart rate when working
out physically; in some cases, this has led to decreased ability to perform
work and daily activities. Some patients also experience an uncomfort-
able sensation of not being able to control their body temperature.


MEdiASTinuM
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7
nOiTCES
B
Sympathetic trunk, thoracic cardiac branch
Brachial plexus, infraclavicular part
Clavicle Vagus nerve, thoracic cardiac branch
Subclavius
Axillary artery and vein Thoracic duct
Recurrent laryngeal nerve
Subclavian artery
First rib
Ligamentum arteriosum
Common carotid artery
Tracheobronchial nodes
Brachiocephalic vein
Vagus nerve Accessory hemiazygos vein
Phrenic nerve
Thoracic aortic plexus, Oesophagus, thoracic part
cardiac plexus
Vagus nerve, pulmonary
Pulmonary plexus plexus
Left pulmonary artery
Thymus Thoracic aortic plexus
Left pulmonary vein
Posterior intercostal
artery and vein
Left main bronchus
Phrenic nerve
Left pulmonary vein Greater splanchnic nerve
Pericardiacophrenic
vein and artery
Parietal pleura,
costal part, cut
Anterior
mediastinal
lymph nodes
Fig. 56.7, cont’d The mediastinum.B, Left lateral aspect. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed,
Elsevier, Urban & Fischer. Copyright 2013.)
extent, the atrioventricular nodes (Ch. 57). Cardiac branches slow the bronchus and lies on the posterior aspect of the right pulmonary hilum.
heart rate and diminish the force of contraction. It has been claimed Here, it gives off posterior bronchial branches that unite with rami from
that the vagi indirectly influence ventricular muscle via their effect on the second to fifth or sixth thoracic sympathetic ganglia to form the
the atrioventricular node, the postganglionic parasympathetic innerva- right posterior pulmonary plexus. Two or three branches descend
tion of the ventricles being sparse. The smaller branches of the coronary from the inferior part of this plexus on the posterior aspect of the
arteries are innervated mainly via the vagus, whereas the larger arteries oesophagus to join a left vagal branch and form the posterior oesopha-
are mainly supplied by sympathetic fibres. Regional patterns of innerva- geal plexus. A vagal trunk containing fibres from both vagi leaves the


tions may explain some particular forms of cardiomyopathies such as plexus and runs inferiorly on the posterior surface of the oesophagus,
apical ballooning (Takotsubo cardiomyopathy). Pulmonary branches entering the abdomen by passing through the diaphragmatic oesopha-
are motor to the circular smooth muscle fibres of the bronchi and geal aperture.
bronchioles, and are therefore bronchoconstrictor; synaptic relays occur
in the ganglia of the pulmonary plexuses. Left vagus
The distribution of the vagi to the abdominal viscera is described in
the relevant chapters.
The left vagus enters the thorax posterior to the left brachiocephalic
vein, between the left common carotid (anterior) and the subclavian
Right vagus
arteries (posterior). It descends through the superior mediastinum and
crosses the left side of the aortic arch, passing posterior to the left pul-
The right vagus nerve descends posterior to the internal jugular vein in monary hilum (see Fig. 56.7B). Superior to the aortic arch, it is crossed
the neck (p. 466) and crosses the first part of the subclavian artery to anterolaterally by the left phrenic nerve; on the arch, it is crossed by the
enter the thorax; the ansa subclavia is lateral, and the phrenic nerve is left superior intercostal vein. Posterior to the left hilum, it divides into
further lateral. It then descends through the superior mediastinum, at the posterior bronchial branches, which unite with rami of the second
first posterior to the right brachiocephalic vein, and then to the right of to fourth thoracic sympathetic ganglia to form the left posterior pulmo-
the trachea and posteromedial to the superior vena cava. Superiorly, the nary plexus. Two or three branches descend anteriorly on the oesopha-
right pleura and lung are lateral; inferiorly, the azygos vein and its gus and join with a ramus from the right posterior pulmonary plexus
arching terminal portion separate the right vagus from the lung and to form the anterior oesophageal plexus. A trunk containing fibres from


pleura (see Fig. 56.7A). The nerve next passes posterior to the right main both vagi descends anterior to the oesophagus and enters the abdomen


Thymus
983
65
RETPAHC
through the oesophageal diaphragmatic aperture. Numerous branches as encircling the left innominate vein (Han et al 1989). Superiorly,
from the anterior vagal and left sympathetic trunks are distributed to extensions into the neck are common, reflecting its bilateral embryonic
the descending thoracic aorta. This pathway transmits the typical origins from the third pharyngeal pouch (p. 619, see Fig. 36.18). Its
intense, excruciating pain of an intramural aortic haematoma from dis- superior poles join at, and extend above, the level of the suprasternal
section or laceration. notch; the left usually extends higher and is seen first behind the strap
muscles during the initial stages of transcervical thymectomy. It some-
times reaches the inferior poles of the thyroid gland or even higher, and
THYMUS
is connected to the thyroid gland by the thyrothymic ligament. Its shape
is largely moulded by adjacent structures. Inferiorly, the right lobe com-
The thymus and the bone marrow are the two primary lymphoid monly lies between the right side of the ascending aorta and the right
organs. The thymus is an encapsulated soft, bilobed organ; the two parts lung, anterior to the superior cava. Anteriorly, from superior to inferior,
are joined in the midline by connective tissue that merges with the lie sternohyoid and sternothyroid, cervical fascia, the manubrium
capsule of each lobe (Figs 56.8–56.9). Capsular tissue may have adhe- sterni, internal thoracic vessels and upper three costal cartilages. The
sions to the fibrous pericardium, which is thinner superiorly and may pleurae lie laterally and the phrenic nerves are anterolateral and infe-
either easily tear or require a limited pericardotomy during thymec- rior; both structures may be injured during thymectomy. Posteriorly,
tomy. The thymus is visible on CT and magnetic resonance imaging the thymus is in contact with the vessels of the superior mediastinum
(MRI) just anterior to the ascending aorta and inferior to the left bra- (the left brachiocephalic vein and the inferior thyroid veins are usually


chiocephalic vein. CT attenuation in younger individuals is homogene- partly embedded in the gland), the superior part of the thoracic trachea
ous, greater than that of the chest wall and cardiac muscles below the and the anterior cardiac surface (right atrium and ventricle). Thoracic
age of 1 year, and similar to that of these muscles after the age of 1 year surgeons performing thymectomy must be aware of the anatomical
(Sklair-Levy et al 2000); the signal intensity with MRI on T-weighted variation in which the upper poles may lie posterior to the left brachio-
2
images is similar to or greater than that of fat. The decline in CT attenu- cephalic vein.
ation with age is secondary to fatty infiltration. Separated thymic tissue is often found scattered around the gland,
and ectopic thymic rests are sometimes discovered in unusual media-
Relations stinal locations. Small accessory nodules may occur in the neck, repre-
senting separated portions, detached during embryological descent,
and sometimes reaching more superiorly than the thyroid cartilage.
The thymus is largest in the early part of life, particularly around
Ectopic intrathyroidal thymi have been reported in children (Segni
puberty, and persists actively into old age despite considerable fibrofatty
et al 2011).
degeneration that sometimes hides the existence of persistent thymic
tissue. The greater part of the thymus lies in the superior and anterior
mediastina; the inferior aspect of the thymus reaches the level of the
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
fourth costal cartilages. In some children, the thymus has been described
Arteries
Thyroid gland
Thymic branches originating from the internal thoracic, inferior and
sometimes superior thyroid arteries supply the thymus and the sur-
rounding mediastinal connective tissue. As no definite hilum exists, the
Trachea
arterial branches either travel along the interlobar septa before entering
the thymus at the junction of the cortex and medulla, or they reach the
Cervical Carotid arteries thymic tissue directly through the capsule.
extensions (low division)
of thymus
Veins
Thymic veins drain to the left brachiocephalic, internal thoracic and
Thymus,
inferior thyroid veins, and occasionally directly into the superior vena


right lobe Thymus,
cava. One or more veins often emerge medially from each lobe of the
left lobe
thymus to form a common trunk opening into the left brachiocephalic
vein and require careful ligation during thymectomy.
Right lung
Lymphatic drainage
The thymus has no afferent lymphatics. Efferent lymphatics arise from
the medulla and corticomedullary junction, drain through the extravas-
cular spaces, accompany the supplying arteries and veins, and end in
Fig. 56.8 The neonatal thymus. the brachiocephalic, tracheobronchial and parasternal nodes.
INNERVATION
The thymus is innervated from the sympathetic chains via the cervico-
thoracic (stellate) ganglia or ansa subclavia and from the vagi. Branches
from the phrenic and descending cervical nerves (inferior roots of the
ansa cervicalis) are distributed mainly to the capsule. The two lobes are
innervated separately through their dorsal, lateral and medial aspects.
During development and before its descent into the thorax, the thymus
is innervated by the vagi in the neck. After its descent, the thymus
receives a sympathetic innervation via fibres that travel along the vessels;
postganglionic sympathetic terminations branch radially and form a
plexus with the vagal fibres at the corticomedullary junction.
MICROSTRUCTURE
5 4 3 2 1 0 1 2 3 4 5
cm The thymus is responsible for the provision of thymus-processed (T)
Fig. 56.9 A thymus from a 9-year-old female (left) and one from an lymphocytes to the entire body, and provides a unique microenviron-
80-year-old male (right). Note the fibrofatty infiltration of the older thymus. ment in which thymocytes (T-cell precursors) undergo development,
(Courtesy of Professor M Kendall.) differentiation and clonal expansion to deliver the exquisitely specific


Mediastinum
983.e1
65
RETPAHC
The roles of the nervous system and other neuroendocrine elements
in the overall biology of the thymus are little understood. Many of the
autonomic nerves are doubtless vasomotor, but other terminal branches
(at least in rodents) ramify among the cells of the thymus, particularly
the medulla, suggesting that they may have other roles. Innervation is
complete by the onset of thymic function. The medulla contains a
number of different types of non-lymphoid cells, including cells posi-
tive for vasoactive intestinal polypeptide and acetylcholinesterase; large
non-myoid cells; and cells containing oxytocin, vasopressin and neuro-
physin, of possible neural crest origin.


MEdiASTinuM
984
7
nOiTCES
Capsule
Epithelial cells
Outer
cortex
Nerve fibre
Blood vessel
Middle
cortex
Interdigitating Fig. 56.11 The medulla of a neonatal thymus, showing three concentric
dendritic cell
Hassall’s corpuscles of varying degrees of maturity, surrounded by
Medulla
Thymic (Hassall’s) closely packed lymphocytes and a few epithelial cells with larger nuclei.
corpuscle
of long cytoplasmic processes, whereas medullary epithelial cells tend
to form more solid cords and Hassall’s corpuscles. Lymphocytes lie
Fig. 56.10 Thymic structure and cellular organization, showing an within the interstices of the mesh or between the cords. Large epithelial
interlobular septum, the cortical circulation and thymocytes within an ‘nurse’ cells may be associated with around 50 or more thymocytes.
epithelial framework. Hassall’s corpuscles are whorls of flattened, concentrically layered
cells, 30–100 µm in diameter, that characterize the thymic medulla (see
Fig. 56.10; Fig. 56.11). Originating prenatally, and increasing in number
T-cell response, simultaneously acquiring immune tolerance to the throughout life, they perhaps remove dying thymocytes because their
body’s own components. These steps involve intimate interactions centres are eosinophilic and partly keratinized, and often contain cel-
between thymocytes, mainly epithelial and antigen-presenting cells and lular debris. Corpuscles with a similar appearance have been described
chemical factors in the thymic environment. The thymus is also part of in the palatine tonsil. (For further reading, see Raica et al (2006),
the neuroimmunological and neuroendocrine axes of the body, influ- Asghar et al (2012).)
enced by and influencing the products of these axes. Its activity there-
fore varies throughout life under the influence of different physiological Other non-lymphocytic thymic cells
states, disease conditions and chemical insults, such as hormones, drugs
and pollutants. The thymus appears to be most active between the ages The thymus also contains cells of the myeloid, fibroblastic and myoid


of 3 and 6 months, when the highest number of total thymocytes are lineages. Myeloid lineage cells include monocytes at the corticomedul-
present (Weerkamp et al 2005). lary junction, mature macrophages throughout but particularly in the
cortex, and interdigitating dendritic (antigen-presenting) cells at the
General architecture
corticomedullary junction and in the medulla. Some dendritic cells are
of lymphoid rather than myeloid origin (see Fig. 4.12). Fibroblasts are
It is useful to consider the embryological origins of the thymus in order found in the capsule, perivascular spaces and medulla but are infre-
to understand its cellular organization. It is derived from a number of quent in the cortex, except in the involute thymus. Myoid cells, which
sources, including epithelial derivatives of the pharyngeal pouches, are relatively rare, are situated mainly in the medulla and at the corti-
mesenchyme, haemolymphoid cells and vascular tissue. In section, the comedullary junction. They are large, rounded cells possessing a central
thymus can be seen to consist of an outer cortex of densely packed nucleus surrounded by irregularly arranged bundles of myofilaments
thymocytes (T-cell precursors) and an inner medulla with fewer lym- with unknown function, although it has been suggested that their con-
phoid cells (Fig. 56.10). Both thymic lobes have a loose, fibrous con- tractions might aid the movement of lymphoid cells across or out of
nective tissue capsule, from which septa penetrate to the junction of the the thymus.
cortex and medulla, and partially separate the irregular lobules, which
are each 0.5–2.0 mm in diameter (see Fig. 56.12). The connective tissue Thymocytes
septa form a route of entry and exit for blood vessels and nerves, and
carry efferent lymphatics. Most migrant cells enter or leave the thymus The cortex is densely packed with small thymocytes (thymic lym-
by this route. In each lobule, the cortex is composed of a superficial phocytes, presumptive T cells; see Ch. 4). They occupy the interstices of


subcapsular cortex (a narrow band of cells immediately beneath the the epithelial reticulum, which they largely obscure in histological sec-
capsule) and a more extensive main cortex. The central medulla of both tions, and form 90% of the total weight of the neonatal thymus. A
thymic lobes is continuous from one lobule to the next. distinct subcapsular zone houses the thymic stem cells and lympho-
blasts undergoing mitotic division. The first stem cells to enter the
Epithelial framework
thymus in the embryo come from the yolk sac and liver during their
haemopoietic phases. During later developmental periods, it is proba-
Unlike other lymphoid structures, in which the supportive framework ble that all thymic lymphocytes originate in the bone marrow before
is chiefly collagenous reticular tissue, the thymus contains a network of passing in the blood stream to the thymus.
interconnected epithelial cells (see Fig. 56.10) that create an appropriate Thymocytes undergo mitosis in all cortical zones as the differentiat-
microenvironment, by cell-to-cell contact and the release of paracrine ing T cells mature, gradually moving deeper into the cortex (Fig. 56.12).
factors, in which thymic lymphocytes (T cells) develop and mature. The processes of thymocyte development and maturation to generate T
Although differing in morphology, all the epithelial cells of the thymus cells depend on the microenvironment provided by epithelial cells,
share a common origin from pharyngeal endoderm. They vary in size dendritic cells, macrophages and fibroblasts. T cells that either fail to
and shape, according to their positions within the thymus. Typically, recognize self-MHC (histocompatibility) molecules or that recognize
they have pale, oval nuclei, a rather eosinophilic cytoplasm and inter- self-antigens die by apoptosis, in order to achieve functional immune
cellular desmosomal attachments. Intermediate filament bundles of reactivity and maintain self-tolerance, respectively. Over 95% of cortical
cytokeratin lie within their cytoplasm. The subcapsular cells form a thymocytes die within the thymus; the surviving T cells migrate through
continuous external lining to the thymus, following its lobulated the walls of venules and efferent lymphatics to enter the circulation and


profile, ensheathing the penetrating vessels, and contributing to the populate secondary lymphoid tissues (for further details of thymocyte
blood–thymus barrier. Other cortical epithelial cells form a loose mesh development, see p. 76).


Thymus
985
65
RETPAHC
Macrophage
lineage cells
Involution due to
Involution due to
accidental stress,
normal ageing
disease
Hypertrophy induced
Phagocytic
gb ry
o
wT3 th, p hr oo rla mc oti nn e,
macrophages
Cortex
Thymocytes
Monocyte
APC
Lymphocytes
CD4+
Prothymocyte CD8–
CD4–
CD8+ Medulla
Apoptotic CD4+
thymocytes CD8– Myoid cell
From bone CD4–
marrow CD8+ Fibroblasts
B
Recirculating
cells
Epithelial
thymoma
Epithelial and Vessels
stromal cells and nerves
Fig. 56.12 The microscopic organization of the thymus at various stages of life and under different conditions. Abbreviations: APC, antigen-presenting
cell; T, tri-iodothyronine hormone.
3
Microcirculation The thymus is largest relative to body mass at birth, weighing
10–15 g. It is typically larger in boys than girls at 6 months of age (Garly
et al 2008). Studies of thymic mass after sudden death have recorded a
Cortex
wide variation at all ages, but the general pattern is that, after increasing
The pattern of blood flow differs in the cortex and medulla. Major
in the first year of life, the mean mass remains fairly constant at 20 g
blood vessels enter the gland at the corticomedullary junction and pass
until the sixth decade, when a reduction occurs. At birth, individual
within each lobe, giving off small capillaries to the cortex and larger
adipocytes are present in connective tissue septa, and increased numbers
vessels to the medulla. Most cortical capillaries loop around at different
are found within the cortex in the second and third decades. Fatty
depths in the cortex and join venules at the corticomedullary junction;
infiltration is usually complete by the fourth decade, when only the
some continue through the cortex and join larger venules running in
medulla and small patches of associated cortex are spared. This process
the capsule that leave the thymus. Sheaths of thymic epithelial cells of
is independent of body mass index (BMI).


the blood–thymus barrier lie between the narrow perivascular space
In children, the gland is more pyramidal in shape and firmer than
of the smaller cortical capillaries and cortical thymocytes (Henry et al
in later life, when the amount of lymphoid tissue is greatly reduced. In
1992). This perivascular space sometimes contains pericytes and, rarely,
the fresh state, it is deep red, reflecting its hypervascularity (see Fig.
neurones.
56.9). With age, it becomes thinner, greyer and increasingly infiltrated
Medulla by yellow adipose tissue. Each of the two lobes is partially divided by
the ingrowth of shallow septa, so that, superficially, the gland appears
Medullary blood vessels are not as well protected by epithelial cells, and
lobulated. As fatty atrophy proceeds, this lobulation becomes more
those of the corticomedullary junction are only partially ensheathed,
distinct. The older thymus may be distinguished from the surrounding
usually on their cortical aspect. Medullary vessels are very variable in
mediastinal fat only by the presence of its capsule. However, even
size; some have short lengths of cuboidal endothelium similar to those
greatly atrophied glands usually contain perivascular areas of persistent
in lymph nodes and mucosa-associated lymphoid tissue (MALT; p. 75).
lymphoid tissue. Thymocyte production and differentiation persist
throughout life, and thymic T cells continue to populate peripheral
DEVELOPMENT lymphoid tissue, blood and lymph.
Congenital anomalies of the thymus
The embryology and prenatal development of the thymus are described
Undescended thymus, accessory thymic bodies and rare cysts of the
on page 619.
third branchial pouch are usually of no clinical significance in isolation.
Patients with thymic agenesis, aplasia and hypoplasia, as in severe
Thymic changes during postnatal life
combined immune deficiency disease (SCID), have reduced lymphocyte
numbers, and early death from infection is common. Most cases are
At birth, the thymus is most often bilobar and is 4–6 cm long, 2.5–5 cm familial, with autosomal recessive genes. In young children, a large


wide and 1 cm thick. The bulkiest part of the gland at this age is imme- normal thymus may press on the trachea, causing attacks of ventilatory
diately above the base of the heart where it covers the phrenic nerves stridor. This condition must be differentiated from other congenital
laterally; the protection of these nerves is mandatory during paediatric conditions such as vascular rings and slings that require surgical
cardiac surgery procedures. The left lobe is longer and thicker than the correction.
right lobe in full-term neonates (Varga et al 2011); during childhood,
the thymus narrows and lengthens, and the cervical portion becomes
less noticeable. Imaging studies of the thorax in normal children reveal THYMECTOMY
that the right lobe of the thymus typically measures 9 mm in thickness
and the left 11 mm. After the age of 20 years, it decreases to 5–6 mm in The thymus is essential for the normal development of lymphoid
thickness (see Fig. 56.12). tissues during neonatal and early postnatal life. Thymectomy during


MEdiASTinuM
986
7
nOiTCES
this period results in hypoplasia of the peripheral lymphoid organs, and ends at the gastric cardiac orifice, level with the eleventh thoracic
wasting and an inability to mount an effective immune response; it is vertebra.
ultimately fatal. By the onset of puberty, when the main lymphoid Generally vertical in its course, the oesophagus normally displays
tissues are fully developed, thymectomy is less debilitating, but effective two shallow curves. Starting in the median plane, it inclines to the left
responses to novel antigens are reduced. as far as the root of the neck, gradually returns to the median plane
Thymectomy is commonly performed for myasthenia gravis, usually near the fifth thoracic vertebra, then deviates leftwards again at the
after referral from a neurologist. The most beneficial effects of thymec- seventh thoracic vertebra before piercing the diaphragm. The oesopha-
tomy are seen in myasthenic females who present with systemic mus- gus also deviates sagittally as it follows the cervicothoracic vertebral
cular weakness; controversial operative groups include the elderly and lordosis. Further inferiorly, it is pushed slightly to the right by the aorta
those with isolated ocular symptoms. before resuming its leftward course towards the oesophageal hiatus. It
is the second narrowest part of the alimentary tract (the narrowest is
Thymoma and myasthenia gravis the vermiform appendix) and is constricted at its start (15 cm from the
incisor teeth, as measured during oesophagoscopy); where it is crossed
anteriorly by the aortic arch (23 cm from the incisor teeth, as measured
Available with the Gray’s Anatomy e-book during oesophagoscopy) and by the left principal bronchus (28 cm
from the incisor teeth, as measured during oesophagoscopy); and as it
passes through the diaphragm (40 cm from the incisor teeth, as meas-
OESOPHAGUS
ured during oesophagoscopy). In children, the length of the oesopha-
gus correlates best with height (Yang et al 2005).
The oesophagus is a muscular tube, 25 cm long in the adult, that con-


nects the pharynx to the stomach (see Figs 56.4, 56.6; Figs 56.13–
56.14). Beginning in the neck, level with the lower border of the cricoid CERVICAL OESOPHAGUS
cartilage and the sixth cervical vertebra, it descends largely anterior to
the vertebral column through the superior and posterior mediastina, The cervical portion of the oesophagus is posterior to the trachea and
passes through the diaphragm, level with the tenth thoracic vertebra, attached to it by loose connective tissue. The recurrent laryngeal
A B Pharyngeal muscles
Common Trachea
Thyroid gland, left lobe
carotid artery
Thyroid gland, right lobe
Common carotid artery
Common
Subclavian Common carotid artery
artery carotid artery Internal jugular vein
Subclavian Internal jugular vein
Oesophagus,
cervical part artery Subclavian artery and vein
Subclavian artery
Brachiocephalic trunk and vein
Right main
bronchus Aortic arch Left brachiocephalic vein
Right brachiocephalic
vein
Ligamentum
arteriosum Tracheal cartilages Brachiocephalic
trunk
Carina
Aortic arch Superior vena cava
Right superior
lobar bronchus Ligamentum arteriosum
Left main
Azygos vein
bronchus
Bronchial branches Tracheal
bifurcation
Thoracic aorta
Left pulmonary
Right main
artery
bronchus
Oesophagus, Left main Right pulmonary
thoracic part bronchus artery
Left pulmonary
Diaphragm, central veins
Oesophageal
tendon hiatus Right pulmonary
Left ventricle veins
Oesophagus, Posterior intercostal
Caval opening abdominal part arteries
Oesophagus,
thoracic part
Right crus of
diaphragm,
Stomach, Diaphragm
lumbar part cardiac part Inferior
vena cava
Inferior phrenic
arteries Central
tendon
Aortic hiatus
Left crus of
Coeliac trunk diaphragm, Thoracic
lumbar part aorta
Abdominal aorta
Oesophageal
hiatus


Fig. 56.13 The oesophagus. A, Anterior view. B, Posterior view. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy,
15th ed, Elsevier, Urban & Fischer. Copyright 2013.)


Mediastinum
986.e1
65
RETPAHC
Thymectomy is performed through a transcervical approach or a Thymic tumours may compress the trachea, oesophagus and large veins
sternotomy, the choice of approach depending on the size and disposi- in the neck, causing hoarseness, cough, dysphagia and venous engorge-
tion of the diseased gland. The cervical approach involves a lower ment of the head and neck. Thymomas tend to have a heterogeneous
transverse incision that includes the sternal heads of both sternocleido- signal intensity on MRI, often developing in one lobe of the thymus
mastoids, permitting an improved access to the substernal plane. Ster- without affecting the other. Many affected patients also have myasthe-
nothyroid and sternohyoid are separated and the superior poles of the nia gravis and other autoimmune conditions. Myasthenia gravis, a
thymus are identified immediately underneath these muscles. A safe chronic autoimmune disease of adults, presents as a diminution in
pre-thymic plane is created by blunt dissection just posterior to the power of repetitive contraction in certain voluntary muscles. Although
sternum, facilitating subsequent mobilization of the gland. The media- there may be more than one condition with these signs, myasthenia
stinal great vessels and the thymic vessels must be carefully identified. gravis is essentially an autoimmune disease in which acetylcholine
The thymic veins are selectively ligated and divided, especially those receptor proteins of neuromuscular junctions are attacked by autoanti-
draining directly into the superior vena cava or the left brachiocephalic bodies. Muscles commonly involved are levator palpebrae superioris,
vein. The smaller arterial branches from the internal thoracic arteries leading to ptosis, and the extraocular muscles, leading to diplopia.
are usually dealt with using electrocautery, care being taken to avoid Other muscles in the face, jaws, neck and limbs may be involved, and
injury to the phrenic nerves (patients are generally not given a paralytic in severe cases, the ventilatory muscles are compromised. Occasional
agent during anaesthesia, in order for the phrenic nerves to be identified Caucasian individuals with myasthenia gravis have a thymoma and


intraoperatively). The thymus generally remains completely encapsu- some have medullary follicular hyperplasia; the latter are predomi-
lated and is separated without difficulty from the pericardium (occa- nantly females younger than 40 years of age with strong expression of
sionally, adhesions necessitate a limited pericardiectomy). Further HLA-B8-DR3, in whom thymectomy often results in symptomatic
inferiorly, a gentle push on the great vessels allows direct visualization improvement. In the absence of a thymoma, the onset of myasthenia
into the aortopulmonary window for complete removal of the thymus gravis occurs after 40 years of age in patients with an HLA-B7-DR2
in this vicinity. phenotype, except for a group in whom weaknesses are restricted to eye
In most cases, the thymus gland is removed completely with both and eyelid movements.
upper and lower poles intact. Careful inspection of the remaining tissue
in the mediastinum is performed to identify any possible anatomical
anomalies that might result in retained thymic tissue after the opera-
tion. The most common anomaly is the unanticipated location of the
upper poles of the thymus behind the left brachiocephalic vein. The
aortopulmonary window is also a common location for thymic tissue
and this area is sometimes difficult to expose with a transcervical
approach. Any suspicious foci of fat in the mediastinum are removed,
and, if necessary, sent for frozen section to ascertain whether or not they
contain thymic tissue.


Oesophagus
987
65
RETPAHC
A B
Inferior thyroid vein Oesophagus, cervical part
Inferior thyroid artery Inferior thyroid artery, Vertebral vein
oesophageal
branches Internal jugular vein Left brachiocephalic vein
Right common
carotid artery Vertebral artery Right subclavian vein
Subclavian artery
Accessory hemiazygos vein
Left common carotid artery
Superior vena cava
Trachea
Posterior intercostal
Thoracic aorta, veins
Oesophageal veins
bronchial branches
Oesophagus,
Oesophagus
thoracic part
Thoracic aorta,
oesophageal branches
Hemiazygos vein
Azygos vein
Left gastric artery,
Diaphragm,
oesophageal branches
caval opening
Diaphragm Diaphragm,
central tendon
Lower
oesophageal veins
Coeliac trunk Oesophagus,
abdominal part
Left gastric
artery Inferior phrenic vein Left gastro-epiploic
vein
Inferior vena cava
Stomach
Left gastric vein
Fig. 56.14 The oesophagus, anterior view. A, Arterial blood supply. B, Venous drainage. (With permission from Waschke J, Paulsen F (eds), Sobotta
Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
nerves ascend on each side in or near the tracheo-oesophageal On the right of the oesophagus, just above the diaphragm, a small,
groove. Posteriorly are the vertebral column, longus colli and the pre- serous infracardiac bursa may occur, representing the detached apex of
vertebral layer of deep cervical fascia. Laterally, on each side, are the the right pneumatoenteric recess.
common carotid arteries and the posterior part of the thyroid gland. The close relationship between the oesophagus, the heart and the
In the lower neck, where the oesophagus deviates to the left, it is aorta constitutes the anatomical basis of transoesophageal cardiovascu-
closer to the left carotid sheath and thyroid gland than it is on the lar ultrasonography. Aortic dissection may be seen in the descending
right. The thoracic duct ascends for a short distance along its left side thoracic aorta in cases of equivocal CT and MRI.


(see Figs 56.5, 56.7B).
ABDOMINAL OESOPHAGUS
THORACIC OESOPHAGUS
The abdominal oesophagus is described in Chapter 64.
The thoracic oesophagus (see Figs 56.13–56.14) is situated a little to
the left in the superior mediastinum between the trachea and the ver- VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
tebral column. It passes behind and to the right of the aortic arch to
descend in the posterior mediastinum along the right side of the
Arteries
descending thoracic aorta. Below, as it inclines left, it crosses anterior
to the aorta and enters the abdomen through the diaphragm at the level
of the tenth thoracic vertebra. From above downwards, the trachea, right The cervical oesophagus is supplied by the inferior thyroid artery (see
pulmonary artery, left principal bronchus, pericardium (separating it Fig. 56.14, p. 458). The thoracic oesophagus is supplied by bronchial
from the left atrium) and the diaphragm are anterior. The vertebral and oesophageal branches of the thoracic aorta (see Fig. 56.14A). Four
column, longus colli, right posterior intercostal arteries, thoracic duct, or five oesophageal branches arise from the anterior surface of the aorta
azygos vein and the terminal parts of the hemiazygos and accessory and descend obliquely to the oesophagus, where they form a vascular
hemiazygos veins, and, near the diaphragm, the aorta are posterior. A chain that anastomoses above with the oesophageal branches of the
long recess of the right pleural sac lies between the oesophagus anteri- inferior thyroid arteries, and below with ascending branches from the
orly and the azygos vein and vertebral column posteriorly in the pos- left phrenic and left gastric arteries. Extensive devascularization of the
terior mediastinum (the azygo-oesophageal recess). oesophagus may lead to acute oesophageal necrosis as in aortic dissec-
In the superior mediastinum, the terminal part of the aortic arch, tion (van der Wal-Visscher et al 2011).


left subclavian artery, thoracic duct, left pleura and the recurrent laryn-
Veins
geal nerve are left lateral relations. In the posterior mediastinum, the
oesophagus is related to the descending thoracic aorta and left pleura.
The right pleura and the azygos vein, as it arches forwards above the Blood from the oesophagus drains into a submucous plexus and thence
right main bronchus to join the superior vena cava, are right lateral into a peri-oesophageal venous plexus, from which the oesophageal
relations. Below the pulmonary roots, the vagus nerves descend in veins arise. Those from the thoracic oesophagus drain predominantly
contact with the oesophagus, the right mainly behind and the left in into the azygos veins and, to a lesser extent, the hemiazygos, intercostal
front; the vagi subsequently unite to form a plexus around the oesopha- and bronchial veins (see Fig. 56.14B). Those from the cervical oesopha-
gus. Low in the posterior mediastinum, the thoracic duct is posterior gus drain into the inferior thyroid vein. The left gastric vein meets the
and to the right of the oesophagus; at higher levels, the duct is posterior, lower oesophageal veins at the oesophageal opening in the lesser cur-
crossing to the left of the oesophagus at about the level of the fifth vature, one of the sites of porto-caval venous anastomoses where
thoracic vertebra, then ascending on the left. variceal transformation can occur in portal hypertension (see below).


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Oesophageal varices
Cirrhosis or fibrosis of the liver affects the vascular tree within the liver,
resulting in a decrease of hepatic vascular compliance, and a likely
increased vascular tone reflecting a reduction in endothelial vasodila-
tors such as nitric oxide. The portal resistance increases, leading to the
formation of a collateral circulation, and there is a concomitant increase
in the systemic and splanchnic blood flow. Porto-systemic shunting of
blood occurs between the short gastric coronary veins and the oesopha-
geal veins, largely as the result of the dilation of pre-existing embryonic
G
channels.
Lymphatic drainage
The oesophagus has an extensive, longitudinally continuous submu-
cosal lymphatic system, which presumably explains remote para-
oesophageal lymphadenopathy in oesophageal carcinoma. Efferent
vessels from the cervical oesophagus drain to the deep cervical nodes
either directly or through the paratracheal nodes. Vessels from the tho-
racic oesophagus drain to the posterior mediastinal nodes and those
from the abdominal oesophagus drain to the left gastric lymph nodes.
Some may pass directly to the thoracic duct.
INNERVATION
The upper oesophagus is supplied by the branches of the recurrent
laryngeal nerve and by postganglionic sympathetic fibres that reach it
by travelling along the inferior thyroid arteries. The lower oesophagus
is supplied by the oesophageal plexus, a wide-meshed autonomic
network that surrounds the oesophagus below the level of the lung SM
roots, and contains a mixture of parasympathetic and sympathetic fibres
Fig. 56.15 The wall of the oesophagus. A stratified squamous, non-
(see Fig. 56.6).
keratinizing epithelium lines the lumen (right). Submucosal glands (G) in
Motor fibres to the striated and smooth muscle of the oesophageal
the submucosa (SM) secrete mucus that lubricates the passage of food.
wall travel in the vagus. Axons derived from neuronal cell bodies in the
(With permission from Dr JB Kerr, Monash University, from Kerr JB 1999
nucleus ambiguus travel via the recurrent laryngeal nerve and supply
Atlas of Functional Histology. London: Mosby.)


cricopharyngeus and the striated muscle of the upper third of the
oesophagus. Axons with cell bodies in the dorsal nucleus of the vagus
pass through the oesophageal plexus and supply the smooth muscle
that makes up the lower two-thirds of the oesophagus, after local relay
sion. The boundary between the oesophageal epithelium and its lamina
in the oesophageal wall. Other branches are given off by the vagus as
propria is distinct but markedly uneven due to tall connective tissue
it travels through the mediastinum, and pass directly to the oesophagus.
papillae invaginating the epithelial base, assisting in the anchorage of
The vagus also carries secretomotor fibres to mucous glands in the
the epithelium to underlying tissues (see Fig. 56.15). These papillae are
oesophageal mucosa, and visceral afferent (sensory) fibres to cell bodies
permanent structures, also unaffected by oesophageal distension, and
in its inferior ganglion.
they are rich in blood vessels and nerve fibres. At the base of the epi-
Vasomotor sympathetic fibres destined for the oesophagus arise
thelium, there is a basal lamina, to which epithelial cells are attached
from the upper 4–6 thoracic spinal cord segments. Those from the
by hemidesmosomes, as occurs in the oral mucosa.
upper ganglia pass to the middle and inferior cervical ganglia, where
Oesophageal epithelium is similar to other stratified squamous epi-
they synapse on postganglionic neurones that give rise to axons that
thelia. It can be divided into a basal, proliferative layer, a parabasal layer
innervate the vessels of the cervical and upper thoracic oesophagus.
of cells undergoing terminal differentiation and a flattened layer of
Those from the lower ganglia pass either directly to the oesophageal
superficial cells or squames that retain their nuclei. The most superficial
plexus or to the coeliac ganglion (via the greater splanchnic nerve),
strata of cells contain a few keratohyalin granules, in addition to keratin
where they synapse; postganglionic axons innervate the distal oesopha-
filaments. The epithelial cell population is constantly renewed by


gus. Afferent visceral pain fibres travel via the sympathetic fibres to the
mitosis in the cuboidal basal and deepest parabasal cells; as they
first four segments of the thoracic spinal cord. Because these segments
migrate towards the lumen, they become progressively polygonal and
also receive cardiac afferents, it is sometimes difficult to distinguish
then more flattened, eventually desquamated at the epithelial surface.
between oesophageal and cardiac pain.
This sequence of events normally takes 2–3 weeks, and is markedly
slower than in the stomach and intestine.
MICROSTRUCTURE The epithelium is an effective protection against mechanical injury
during swallowing because of its thickness and the presence of mucus
at its surface. However, protection is limited by repeated exposure to
The tissues forming the thoracic oesophageal wall, from the lumen
the strongly acidic, protease-rich secretions of the stomach, as occurs
outwards, are the mucosa (consisting of epithelium, lamina propria and
abnormally during reflux. Failure of the lower oesophageal sphincter
muscularis mucosae), submucosa, muscularis externa and adventitia
allowing reflux results in ulceration and fibrosis, accompanied by
(Fig. 56.15).
dysphagia/odynophagia, with possible epithelial metaplasia to a
gastric-like mucosa (Barrett’s mucosa), or to more overt neoplastic
Mucosa
changes.
The mucosa is thick. At the gastro-oesophageal junction, a jagged Langerhans cells Langerhans cells are present in the oesophageal
boundary line separates the greyish-pink smooth oesophageal mucosa epithelium. They are immature dendritic cells and resemble those
from the reddish-pink gastric mucosa, the latter covered by minute found in the epidermis. They perform similar antigen-processing and
bulges and depressions. Throughout its length, the oesophageal lumen antigen-presenting roles, which are important in immunostimulation
is marked by deep longitudinal grooves and ridges, which disappear of naïve T cells and mucosal defence.
when the lumen is distended, otherwise obliterating it.
Lamina propria
Epithelium
The oesophageal lamina propria contains scattered groups of mucosa-


The epithelium is non-keratinized, stratified squamous, and is continu- associated lymphoid tissue (MALT), especially prominent near the
ous with that of the oropharynx. In humans, this protective layer is gastro-oesophageal junction. Small tubular mucous glands occur in this
quite thick (300–500 µm) and is not affected by oesophageal disten- region and also at the oesophago-pharyngeal junction.


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Varices in the distal oesophagus are easily visible at endoscopy
because they are situated superficially in the lamina propria. The blood
from the superficial veins drains into a superficial venous plexus, then
into a deeper intrinsic venous plexus and finally into the peri-
oesophageal veins via perforating veins. Bidirectional flow is normally
possible in this region, a phenomenon that permits pressure changes
during breathing and Valsalva manœuvres. However, in portal hyper-
tension, the valves within the perforating vessels become incompetent
and blood flow is retrograde, causing dilation of the deep intrinsic
veins. The greater pressure within this region predisposes the varices to
brisk and life-threatening bleeding. Treatment is directed towards con-
trolling the formation of a collateral circulation and the obliteration of
varices that are susceptible to bleeding, and is achieved by paravariceal
endoscopic injection of a sclerosant, which causes obliteration of the
varices as a result of thrombus formation. Fibrosis is also induced
within the mucosa, which reduces the formation of new collateral
vessels. Alternatively, rubber bands may be applied in an attempt to
ligate the varices. Bleeding from varices is associated with a mortality
rate of 25%, reflecting the problems of rebleeding and underlying
comorbidity.


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Muscularis mucosae OESOPHAGEAL SPHINCTERIC MECHANISMS
The muscularis mucosae is composed mainly of longitudinal smooth
muscle and forms a thin sheet near the epithelium, the contours of Radiological studies show that swallowed food stops momentarily in
which it follows closely. At the pharyngeal end of the oesophagus, it the gastric end of the oesophagus, before entering the stomach (see Fig.
may be absent or represented only by sparse, scattered bundles; below 56.18), suggesting the presence of a sphincter at this point. In the past,
this, it becomes progressively thicker. The longitudinal orientation of there was much controversy surrounding the reason for this behaviour
its cells changes to a more plexiform arrangement near the gastro- because only slight thickening of the muscle coat has been found in
oesophageal junction. The ducts of the oesophageal glands pierce the humans. There is now ample physiological and clinical evidence that
muscularis mucosae. closure depends on two major mechanisms. The more important of
these is the lower oesophageal sphincter, a specialized zone of circular
Submucosa smooth muscle surrounding the oesophagus at its transit through the
diaphragm and for much of its short abdominal course. This region of
the oesophagus is maintained under tonic contraction, except during
The submucosa loosely connects the mucosa and the muscularis
swallowing, when it relaxes briefly to admit ingesta to the stomach, and
externa, penetrating the longitudinal ridges of the oesophageal lumen.
during vomiting. Intramural plexuses of the enteric nervous system and
It contains larger blood vessels, nerves and mucous glands. Its elastic
the neural release of nitric oxide contribute to its relaxation. The second
fibres aid closure of the oesophageal lumen after peristaltic dilation.
mechanism is a functional external sphincter provided by the right crus
Oesophageal glands of the diaphragm, which encircles the oesophagus as it passes into the
Groups of small tubule-acinar oesophageal glands mainly lie in the abdomen and is attached to it by the phreno-oesophageal ligament.
submucosa, each sending a single long duct through the intervening Fluoroscopy, electromyography and manometry have shown that its


layers into the lumen. They are composed mostly of mucous cells, with muscular fibres contract around the oesophagus during inspiration and
some serous cells that secrete lysozyme. Close to the pharynx and when intra-abdominal pressure is increased, thus helping to prevent
stomach, the glands are simpler in form and restricted to the lamina gastro-oesophageal reflux, even when the lower oesophageal sphincter
propria of the mucosa (not submucosa). The mucosal mucous glands is inhibited experimentally with atropine. The relative importance of
of the abdominal oesophagus closely resemble the gastric cardiac these two agents in the prevention of oesophageal reflux is still a matter
glands, and are therefore named oesophageal cardiac glands. for debate. Clinically, there is a good correlation between this condition
and lower oesophageal sphincter dysfunction in some cases, whereas in
Muscularis externa others, failure of the diaphragmatic component, as seen in hiatus
hernia, appears to be a major factor. The anatomical configuration
of the gastro-oesophageal orifice may also play some part in these
The muscularis externa is up to 300 µm thick, and consists of the outer
processes.
longitudinal and inner circular layers typical of the intestine. The thicker
longitudinal layer exists as a continuous coat of fibres that extends
Swallowing
almost the entire length of the oesophagus, except posterosuperiorly,
3–4 cm inferior to the cricoid cartilage, where it diverges as two fascicles
that ascend obliquely and anteriorly, passing deep to the lower border The oesophageal phase of swallowing is described on page 584.
of the inferior constrictor, and ending in a tendon that attaches superi-
orly to the posterior ridge of the cricoid lamina. The V-shaped space Vomiting
between these fascicles is filled by the circular oesophageal muscle
fibres, thinly covered inferiorly by decussating longitudinal fibres and
In the initial phase of vomiting, the lower oesophageal sphincter
superiorly by the inferior constrictor, predisposing to the oesophageal
and peri-oesophageal crural fibres simultaneously relax and rapid
diverticulum (Zencker).
diaphragmatic and abdominal muscular contraction commences,
Accessory slips of smooth muscle sometimes pass between the
increasing intra-abdominal pressure.


oesophagus and left pleura or the root of the left principal bronchus,
trachea, pericardium or aorta. Some consider these slips to fix the
oesophagus to these structures, but they actually equilibrate the normal OESOPHAGEAL DYSMOTILITY
physiological changes in position, shape and dimensions of the various
organs between which they extend. Superiorly, the circular fibres blend
Oesophageal dysmotility encompasses disorders of the upper and
posteriorly with the inferior pharyngeal constrictor, and anteriorly, the
lower oesophageal sphincters (discussed in detail in the section on
uppermost fibres attach to the lateral margins of the tendon of the two
gastro-oesophageal reflux), congenital anomalies such as atresia, and
longitudinal fasciculi of the oesophagus. Inferiorly, the circular muscle
achalasia. Upper oesophageal sphincter dysfunction is usually neuro-
is continuous with the oblique layer of muscle fibres in the stomach
logical, often brainstem disease impairing relaxation of cricopharyn-
wall.
geus with resultant dysphagia and aspiration as demonstrated by
In the upper third of the oesophagus, the muscularis externa is
videofluoroscopy.
formed by skeletal muscle; in the middle third, smooth muscle fascicles
Achalasia of the cardia is a primary motor disorder of the oesopha-
intermingle with striated muscle; and this increases distally such that
gus in which there is failure of relaxation of the cardial-oesophageal
the lower third contains only smooth muscle. This is also reflected by
sphincter and loss of peristalsis in the oesophageal body from degenera-
the innervation pattern of the oesophagus (see above).
tion of myenteric plexus neurones. Dysphagia, regurgitation of undi-
gested food and retrosternal chest pain result and a posteroanterior
OESOPHAGOSCOPY AND chest radiograph may show dilation of the oesophagus and retention
TRANSOESOPHAGEAL ULTRASOUND of food products as a mottled, double-contoured mediastinal widening.
Barium swallow shows a classic ‘bird-beak’ appearance as a result of
failure of relaxation of the lower oesophageal sphincter and an absence


Available with the Gray’s Anatomy e-book of peristalsis. Oesophageal pressure manometry demonstrates absent or
impaired relaxation of the lower oesophageal sphincter. Treatment
options are endoscopic pneumatic balloon dilation or laparoscopic
BARIUM STUDIES cardiomyotomy (Heller’s myotomy). Alternatively, intrasphincteric
injection of botulinum toxin may be offered in frail patients and confers
lower morbidity and mortality.
Available with the Gray’s Anatomy e-book
Diffuse oesophageal spasm may present with dysphagia and chest
pain. It is characterized by abnormal oesophageal contractions on
barium swallow, and produces simultaneous segmental contractions
DEVELOPMENT
that obliterate the oesophageal lumen to produce a ‘corkscrew
oesophagus’. Manometry also demonstrates these tetanic contractions.
The development of the oesophagus is described on page 1048. Non-specific oesophageal motility disorder occurs with ageing (presby-
oesophagus) and is characterized by a decreased incidence of normal
Tracheo-oesophageal fistula
or even absent peristalsis after swallowing, often accompanied by repet-
itive tertiary contractions and failure of relaxation of the lower oesopha-
Tracheo-oesophageal fistula is described on page 930. geal sphincter. Oesophageal dysmotility is also seen in scleroderma and


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Oesophagoscopy, a component of superior digestive endoscopic examin- it is at its thinnest, often corresponding to an area of mucosa with no
ation, may be indicated in patients with persistent non-cardiac chest muscular covering bordered by the pharyngeal inferior constrictor and
pain, dysphagia, odynophagia (painful swallowing) or symptoms of cricopharyngeus. Mortality from oesophageal perforations is 20% and
reflux that include nocturnal cough. The endoscope is passed orally results from mediastinitis and necrotizing infection. Presenting symp-
under direct vision with the patient in a lateral decubitus position, with toms include thoracic pain, odynophagia, haematemesis, subacute sur-
or without sedation, and manœuvred into the oesophageal inlet when gical emphysema, tachycardia, breathlessness and, in advanced cases,
the patient is asked to swallow; once through, the endoscope is advanced septic shock. Diagnosis and repair within 24 hours is associated with a
slowly under direct vision. The mucosa normally appears whitish pink, better prognosis and a mortality rate of between 10% and 15%, whereas
changing to red at the squamocolumnar junction (Z line) near the dia- late diagnosis has a much greater mortality rate. For a perforation in
phragmatic hiatus. Cranial displacement of the Z line by more than 2 cm the upper two-thirds of the thoracic oesophagus, a right thoracotomy
is indicative of a hiatus hernia. There may be slight extrinsic compression in the fifth and sixth intercostal space is performed. The lower third of
by the aorta and the left principal bronchus. the oesophagus is approached through a left thoracotomy in the sixth
Endoscopic transoesophageal ultrasound permits assessment of the and seventh intercostal space. The perforation is closed in layers after
oesophageal wall and para-oesophageal structures, such as lymph any necrotic tissue has been debrided.
nodes and the heart and aorta. Numerous surgical and percutaneous
cardiovascular procedures are guided by transoesophageal echography. A double-contrast barium swallow with fluoroscopy enables anatomical


The technique is more sensitive than CT in detecting mediastinal nodal and functional assessment of the oesophagus (see Fig. 56.18). A stand-
metastases, allowing those less than 10 mm in size to be assessed. ard examination involves the patient swallowing a barium solution and
Normal lymph nodes cannot be identified easily by endoscopic ultra- gas granules, and images are taken in the erect, supine and prone
sound because they have the same echogenicity characteristics as sur- recumbent positions. The upright posture fully dilates the oesophagus
rounding tissue; a hypoechoic or inhomogeneous echo portrayal on and is useful in evaluating any constrictions. (The narrow tubular
ultrasound is considered more suspicious of malignancy. Endoscopic lumen of the oesophagus is normally indented slightly by the aortic
ultrasound-guided fine needle aspiration allows accurate diagnosis for arch and the left principal bronchus.) The supine view allows better
para-oesophageal nodes. Transbronchial fine needle aspiration is an evaluation of any motor dysfunction and varices, and moving into the
alternative approach for sampling mediastinal nodes, guided by CT or prone position provokes underlying gastro-oesophageal reflux. Both
positron emission tomography (PET) CT findings. repeating single digital images and cine loops of fluoroscopy can be
obtained. The fluoroscopic images demonstrate defective opening of
Oesophageal rupture the pharyngeal oesophageal sphincter and the nature of the contrac-
tions in the body of the oesophagus. The cardio-oesophageal sphincter
can be assessed in achalasia. Other abnormalities, such as hiatus hernia
The majority of oesophageal ruptures are iatrogenic, and occur during
and areas of narrowing or dilation of the oesophagus, may be demon-
the instrumentation of the oesophagus during simple endoscopy, endo-
strated. Mucosal relief images are obtained once the bulk of the contrast
scopic intervention including dilation, and nasogastric tube placement.
media has passed into the stomach, and this provides fine mucosal
Other causes are barotrauma, foreign bodies and oesophageal carci-
detail. Cross-sectional imaging is usually used for the preoperative plan-
noma. Barotrauma occurs with intense retching and vomiting that
ning and staging of oesophageal tumours, and is of value in radio-


usually cause longitudinal tearing in the posterior wall of the thoracic
therapy planning.
oesophagus (Boerhaave’s syndrome). Overall, locations of oesophageal
perforation are 60% thoracic, 25% cervical and 15% abdominal. Per-
foration in the cervical oesophagus occurs in the posterior wall, where


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other connective tissue diseases where atrophic smooth muscle is NORMAL MEDIASTINAL CONTOURS ON A LATERAL
replaced by fibrous tissue in the submucosa and lamina propria. CHEST RADIOGRAPH
On a lateral view, the cardiac silhouette is seen above the anterior, hori-
GASTRO-OESOPHAGEAL REFLUX
zontal part of the diaphragm (Fig. 56.17). Due to the nomenclature of
the cardiac chambers reflecting their prerotational embryonic state, the
Gastro-oesophageal reflux is described in Chapter 64.
right ventricle and left atrium form the anterior and posterior cardiac
contours, respectively. Posteriorly, both the descending thoracic aorta
HIATUS HERNIA and the oesophagus in the posterior mediastinum may be seen; the
oesophagus can be visualized with swallowed air or barium on a chest
radiograph or fluoroscopically in the barium swallow examination (Fig.
Hiatus hernia is described in Chapter 55.
56.18). The compressive effect on the oesophagus of a dilated left
atrium will be readily identified during barium swallow. Superiorly, the
MEDIASTINAL IMAGING less dense trachea and main bronchi are recognizable, the left principal
bronchus appearing almost circular, seen end-on due to its more
Mediastinal structures may be viewed using X-rays, CT and MRI (see
Commentary 7.1).
NORMAL MEDIASTINAL CONTOURS ON A FRONTAL
CHEST RADIOGRAPH
1
In the posteroanterior (PA) chest radiograph, the X-ray beam enters the
2
back and exits the anterior chest wall during a full inspiratory breath-
hold. The patient stands and elevates and abducts the arms over the
radiographic detector; this protracts the scapulae and depresses the
3
medial ends of the clavicles to clear the peripheral lung fields and
apices, respectively. In this view, the heart and large blood vessels appear 4
as the ‘mediastinal silhouette’ (Fig. 56.16). Forming its left border,
superior to inferior, are the aortic arch (‘aortic knuckle’, sometimes with
the left superior intercostal vein visible – the ‘aortic nipple’), left pul-


monary artery and left ventricle. The descending aorta is projected as a
continuous left paravertebral border to the diaphragm. The right border
is delineated by structures containing deoxygenated blood: superior to
inferior, the right brachiocephalic vein, superior vena cava, right atrium
and thoracic inferior vena cava. The right paratracheal stripe (up to
3 mm) is seen with the oval silhouette of the azygos arch at its lower
margin.
Dilation or displacement of any of these structures accentuates the
normal bulges on the borders of the mediastinal silhouette; thus an
enlarged left auricle is seen between the left principal pulmonary artery
and left ventricle as in mitral valve stenosis. Pulmonary vessels associ-
Fig. 56.17 A lateral radiograph of the adult female chest. Key: 1,
ated with the lung roots form the hilar contours. Sometimes seen are retrosternal line (fat); 2, posterior tracheal line; 3, right principal bronchus;
the anterior junctional line, representing supracardiac lung apposition 4, bronchus intermedius.
(projects up into the neck because of the obliquity of the superior
thoracic aperture), and inferiorly, the posterior junctional line, repre-
senting pleural apposition posterior to the oesophagus. The azygo-
oesophageal line is sometimes seen, representing the medial border of
the right lung in the azygo-oesophageal recess. The paraspinal lines are
also visible parallel to the right and left margins of the thoracic spine.
1
4 1
2
2
5
3
Fig. 56.16 A posteroanterior (PA) radiograph of the adult female chest. Fig. 56.18 An oblique radiograph of the thorax during barium swallow.
Key: 1, trachea; 2, azygos vein; 3, right atrial border; 4, aortic arch; 5, left Key: 1, indentation from aortic arch; 2, indentation from left principal
ventricular border. bronchus.


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An accessory lung fissure, the azygos fissure, is rarely present and
seen in 0.5% of PA chest radiographs, extending from the lung apex to
the right tracheobronchial angle. The azygos arch width should be no
more than 5 mm, but may measure up to 10 mm in the third trimester
of pregnancy as a result of a physiological blood volume increase and
the fact that flow through the inferior vena cava may be diminished as
a result of compression by the uterus, with compensatory drainage
through the azygos system. Similarly, congenital inferior vena cava
interruption at the diaphragm or acquired inferior vena cava thrombo-
sis enlarges the azygos vein.


Mediastinal imaging
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RETPAHC
horizontal lie. The oesophagus is directly posterior to the trachea, and lymphadenopathy. The thoracic inferior vena cava is visible in the
the adjacent anterior oesophageal and posterior tracheal walls appear majority of patients as it drains into the right atrium.
as the posterior paratracheal line, seen in the majority of lateral radio-
graphs (normally less than 5 mm).
The aortic arch and its main branches, anterior to the trachea, CT AND MRI OF THE MEDIASTINAL SPACES
produce faint shadows in the superior mediastinum. The brachio-
cephalic veins are visible as an extrapleural bulge directly posterior to CT provides excellent mediastinal delineation (Figs 56.19–56.20) with
the manubrium. Retrosternal lung should always be seen; if it is absent, intravenous contrast enhancement more readily distinguishing normal
this raises a strong suspicion of a superior mediastinal tumour or anatomy from pathological lymph nodes and tumours. The hilar,
5
1
1
2
6
3 2
7 6
4 8
9 3 7
4
5
A
B
8
1 1
2 8
2 5
3 9
3
10
4
4
6 11
5
6 12
7
7
C D
5
1
2
6
3
7
4
E
Fig. 56.19 Axial CT thoracic sections. A, At the level of the first costochondral junction. Key: 1, manubrium; 2, right brachiocephalic trunk; 3, right
brachiocephalic vein; 4, trachea; 5, scapula; 6, left brachiocephalic vein; 7, left common carotid artery; 8, left subclavian artery; 9, oesophagus.
B, At T3 level. Key: 1, brachiocephalic vein; 2, pretracheal space; 3, trachea; 4, oesophagus; 5, pectoralis major; 6, left subclavian artery arising from


brachiocephalic trunk (normal variant); 7, left subclavian artery; 8, scapula. C, At T4 level. Key: 1, anterior junction; 2, superior vena cava; 3, pretracheal
space; 4, trachea; 5, arch of aorta; 6, oesophagus; 7, scapula. D, At T6 level. Key: 1, ascending aorta; 2, superior vena cava; 3, right pulmonary artery;
4, right principal bronchus; 5, subcarinal space; 6, oesophagus; 7, azygos vein; 8, trunk of pulmonary artery; 9, left superior pulmonary vein; 10, left
principal bronchus; 11, inferior branch of the left pulmonary artery; 12, descending aorta. E, At T7 level. Key: 1, aortic root; 2, left atrium; 3, oesophagus;
4, azygos vein; 5, right ventricular outflow tract; 6, left inferior pulmonary vein; 7, descending aorta.


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1
2
3
4
5
6
A B
1
1
2
2
3 3
4 4
5
5
6
6
7
7 8
C D
1
2
3
4
5
6
E F
Fig. 56.20 Serial coronal thoracic CT sections. A, Key: 1, right brachiocephalic vein; 2, left brachiocephalic vein; 3, pulmonary trunk; 4, ascending aorta;
5, left ventricle; 6, right atrium. B, As A, but with lung window settings; horizontal (minor) fissure arrowed. C, Key: 1, brachiocephalic trunk; 2, left
common carotid artery; 3, aortic arch; 4, superior vena cava; 5, pulmonary trunk; 6, left ventricle; 7, abdominal aorta. D, Key: 1, right subclavian artery;
2, trachea; 3, aortic arch; 4, left main pulmonary artery; 5, right main pulmonary artery; 6, left superior pulmonary vein; 7, left atrium; 8, descending
thoracic aorta. E, Key: 1, left subclavian artery; 2, trachea; 3, posterior aortic arch; 4, left main pulmonary artery; 5, left atrium; 6, descending thoracic
aorta. F, As E, but with lung window settings.


993
65
RETPAHC
Key references
pretracheal, subcarinal, right paratracheal, posterior tracheal and aorto- and on the left side is the oesophagus. All these areas are in direct
pulmonary window stations are common sites of lymph node metas- continuity with each other and are inspected during transcervical
tases in lung cancer. mediastinoscopy.
The pretracheal space, as seen on CT, is bordered by the trachea The junctional areas are where the two lungs approach each other.
posteriorly, the superior vena cava and right brachiocephalic vein ante- The anterior junction lies between the great vessels, posterior margin of
riorly, and the descending aorta and superior pericardial sinus to the the chest wall and the lungs where the left brachiocephalic vein, highest
left. The aortopulmonary window is located between the aortic arch mediastinal nodes, thymus and phrenic nerves are located. The poste-
superiorly and the left pulmonary artery inferiorly; the trachea forms rior junction is an area posterior to the trachea and is where the lungs
its medial border and the left lung its lateral border. The right paratra- appose. The paraspinal area lies between the lateral margins of the spine
cheal space lies between the right lung and the trachea on its anterola- and the lungs where the intercostal vessels, the ganglionated sympa-
teral aspect; the posterior tracheal space between the lung and the thetic chain and small lymph nodes are located. The retrocrural space,
posterolateral aspect of the trachea; and the subcarinal space inferior between the diaphragmatic crura and vertebral bodies, is traversed by
to the carina bounded by the principal bronchi. On the right, the the aorta, azygos venous system, thoracic duct, intercostal arteries, sym-
azygo-oesophageal recess is located posterior to the subcarinal space pathetic chains and splanchnic nerves.
KEY REFERENCES
Deso S, Ludwig B, Kabutey NK et al 2012 Lymphangiography in the diag- studies are described from macroscopic, clinical and evolutionary anatomical
nosis and localization of various chyle leaks. Cardiovasc Intervent viewpoints, together with their applications in improving surgical technique


Radiol 35:117. and for future evaluation in regenerative medicine.
A description of the unparalleled abilities of lymphangiography (LAG)
Kuntz A 1927 Distribution of the sympathetic rami to the brachial plexus:
highlighting the added benefit of post-LAG CT imaging in the diagnosis and
its relation to sympathectomy affecting the upper extremity. Arch Surg
localization of chyle leaks. The retained utility of LAG is demonstrated
15:871–7.
despite the development of conventional CT, MRI and nuclear medicine
A description of the significant number of individuals in whom the
imaging.
intrathoracic somatic branches from the second thoracic spinal nerve join
Doerr CH, Miller DL, Ryu JH 2001 Chylothorax. Semin Respir Crit Care Med the first thoracic spinal nerve. These ‘Kuntz’s nerves’ join the lower part of
22:617. the brachial plexus without passing through the stellate ganglion, explaining
An explanation of how injury or disease of the thoracic duct or its major the incomplete sympathetic blockade of the upper extremities in stellate
tributaries can lead to a chylous effusion, diagnosed by fluid assaying for ganglion blockade.
triglyceride content and lipid electrophoreses for chylomicrons. Conservative
Yoshioka K, Niinuma H, Ohira A et al 2003 MR angiography and CT
management options include observation, treatment of the underlying
angiography of the artery of Adamkiewicz: noninvasive preoperative
disease, strict medium-chain triglyceride diet or total parenteral nutrition,
assessment of thoracoabdominal aortic aneurysm. RadioGraphics
thoracocentesis, tube thoracostomy with chemical pleurodesis or thoracic duct
23:1215–25.
embolization. Surgical management includes pleurectomy, talc poudrage,
An exploration of how the artery of Adamkiewicz must be identified in
pleuroperitoneal shunting or repair/ligation of the thoracic duct.
patients with thoracoabdominal aortic aneurysm to aid surgical planning
Kawashima T 2011 Anatomy of the cardiac nervous system with clinical and and to avoid postoperative paraplegia. It is difficult and very dangerous to