desire to reduce donor site morbidity, led to the first description of a
to satisfy an increasing demand for breast reconstruction in an era when
‘perforator’ flap based on the same vessels (Allen and Treece 1994). This
silicone implants were under scrutiny because of safety fears and pro-
is the DIEP flap, which captures the same soft tissue area of the abdomen
posed links with autoimmune diseases. Further developments to maxi-
for reconstruction, but attempts to avoid injury to rectus abdominis by
mize the volume available for autologous reconstructions of small to
dissecting the perforating vessels through the muscle rather than by
medium-sized breasts included harvesting larger skin paddles from the
sacrificing it. Some authors have identified fewer donor site bulges and
back and burying them beneath the breast skin envelope after
herniae with DIEP flaps compared with TRAM flaps (Blondeel et al
de-epithelializing their surface (Papp et al 1988), and inclusion of addi-
1997), and it is for this reason that DIEP flaps are the preferred choice,
tional fat pads in the back to increase flap volume (Delay et al 1998).
if possible. However, the perforating vessels are not always anatomically
Despite the enhancements to the latissimus dorsi flap, the lower
favourable for allowing safe harvest of the flap. Many clinicians have
abdominal region provides a plentiful and more reliable source of
adopted radiological studies (CT angiogram, duplex or MR angiogram)
tissue for reconstructive surgeons and also avoids the sometimes
to determine the calibre and position of the vessels preoperatively for
troublesome and often unsightly dorsal donor site wound. DIEP or
more accurate surgical planning (see Fig. 53.26).
MS-TRAM flaps are generally considered the first choice for breast
reconstruction when the tissues are adequate.


Chest wall and breast
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Changes during the menstrual cycle
Changes occur in the breast tissues in the menstrual cycle. In the follicu-
lar phase (days 3–14), the stroma becomes less dense. Various changes,
including luminal expansion, take place in the ducts; there are occa-
sional mitoses but no secretion. In the luteal phase (days 15–28), there
is a progressive increase in stromal density and the ducts have an open
lumen that contains secretion, associated with flattening of the epithe-
lial cells. Cell proliferation is maximal on day 26 and thereafter the
ductal system undergoes reduction; epithelial cell apoptosis is greatest
on day 28 of the cycle. There are also changes in blood flow, which are
greatest at mid-cycle, and an increase in the water content of the stroma
in the second half of the menstrual cycle.
Postmenopausal
Progressive atrophy of lobules and ducts occurs after the menopause,
and there is fatty replacement of glandular breast tissue. A few ducts
may remain. The stroma becomes much less cellular and collagenous
fibres decrease. The amount of adipose tissue varies widely between
individuals, and the breast may return to a condition similar to the
prepubertal state.
CHANGES ASSOCIATED WITH PREGNANCY
AND LACTATION
Pregnancy
Fig. 53.28 Milk lines.
As the output of oestrogen and progesterone, produced first by the
corpus luteum and later by the placenta, rises during pregnancy, the
intralobular ductal epithelium proliferates and the cells increase in size;
occurs in most cases in the thoracic region, just inferior to the normal
the number and length of the ductal branches therefore increase. Alveoli
breast (90%), but may also occur in the axillary (5%) and abdominal
develop at their termini and expand as their cells and lumina fill with
regions (5%) and even on to the medial thigh. Polythelia occurs
newly synthesized and secreted milk. The myoepithelial cells, which are
along the same mammary line but no underlying glandular tissue devel-
initially spindle-shaped, become highly branched stellate cells, espe-
ops. This condition is rare in the female population but it is more


cially around the alveoli. Adjacent myoepithelial cells intermesh to
common in males, in whom the accessory nipple may be mistaken for
form a basket-like network around the alveoli and ducts, interposed
a mole.
between the basal lamina and the luminal cells (see Fig. 2.3). Their
cytoplasm contains actin and myosin filaments, and they are contractile
Congenital inversion of nipple
(see Fig. 2.4). There is a concomitant reduction in adipose tissue in the
stroma. The numbers of lymphocytes, including plasma cells, and eosi-
Congenital inversion of the nipples occurs rarely in the female popula- nophils increase greatly. Blood flow through the breast increases.
tion and is almost always bilateral. The majority of the cases are umbili- Secretory activity in the alveolar cells rises progressively in the latter
cated, i.e. the nipple can be easily pulled forwards from its depressed half of pregnancy. In late pregnancy, and for a few days after parturition,
position underneath the areolar surface. The condition is thought to be their product is different from later milk and is known as colostrum,
due to failure of proliferation of the mesenchymal tissue, which fails to characteristically low in lipid but rich in protein and immunoglobulins.
push the nipple out. The remaining cases are due to invagination of the Proliferation of the glandular breast parenchyma results in an overall
nipple. Apart from psychological implications, inversion of the nipple increase in breast size through gestation.
may cause recurrent mastitis and difficulty with breast feeding. The
abnormality may be corrected surgically. Lactation
True milk secretion begins a few days after parturition as a result of a
AGE-RELATED CHANGES
reduction in circulating oestrogen and progesterone, a change that
appears to stimulate production of prolactin by the anterior hypophy-
Prepuberty
sis. Milk distends the alveoli so that the cells flatten as secretion increases
(see Fig. 53.23B; Fig. 53.30). The alveolar cell cytoplasm accumulates
The neonatal breast contains lactiferous ducts but no alveoli. Until membrane-bound granules of casein and other milk proteins, and these


puberty, little branching of the ducts occurs, and any slight mammary are released from the apical plasma membrane by membrane fusion
enlargement reflects the growth of fibrous stroma and fat. (merocrine secretion; see Fig. 2.6). Lipid vacuoles are formed directly
in the apical cytoplasm as small lipid droplets that fuse with each other
Puberty to create large ‘milk vacuoles’ up to 10 µm across. These are released as
intact lipid droplets with a thin surround of apical plasma membrane
In the postpubertal female, the ducts become branched on stimulation and adjacent cytoplasm (apocrine secretion; see Fig. 2.6). On hormonal
by ovarian oestrogens. The ends of the branches form solid, spheroidal stimulation by oxytocin, myoepithelial cells contract to expel alveolar
masses of granular polyhedral cells: the potential alveoli. Oestrogens secretions into the ductal system in readiness for suckling.
also promote adipocyte differentiation from mesenchymal cells in the After the onset of lactation, there is a gradual reduction in the
interlobar stroma. Breast enlargement at puberty is mainly a conse- numbers of lymphocytes and eosinophils in the stroma, although
quence of lipid accumulation by these adipocytes. plasma cells continue to synthesize immunoglobulin A (IgA) for secre-
From puberty onwards, externally recognizable breast development tion into the milk. Alveolar cells take up IgA synthesized by adjacent
(thelarche) can be divided into five separate phases (Fig. 53.29): eleva- plasma cells by endocytosis at their basal surfaces and secrete it apically,
tion of the breast bud (phase I); glandular subareolar tissue is present as dimers complexed to the epithelial secretory component.
and both nipple and breast project from the chest wall as a single mass
Post lactation
(phase II); the areola increases in diameter and becomes pigmented,
and there is proliferation of palpable breast tissue (phase III); further
pigmentation and enlargement occur in the areola, so that the nipple When lactation ceases, which may be after as long as 31 years, the
2
and areola form a secondary mass anterior to the main part of the breast secretory tissue undergoes some involution but the ducts and alveoli


(phase IV); and a smooth contour to the breast develops (phase V). never return completely to the pre-pregnant state. Two major processes


Interventional access to thoracic viscera
951
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A
Pre-adolescent 11 years 12 years 13 years 14 years 16 years
B
Breast
Areolar
diameter
Pre-adolescent Elevated Subareolar tissue and Base of breast expands Nipple and areola form a As breast adopts adult form,
breast bud nipple elevated as as subareolar tissue and secondary projection from the a smooth contour to the
breast bud develops nipple continue to develop breast mass; nipple protrudes nipple/areolar complex develops
more proudly from areola
Fig. 53.29 Pre- and postpubertal development and structure of the female breast, demonstrating changes in the contour of the breast.
are responsible for the regression of the alveolar–ductal system: a reduc- et al 1973) and symptomatology. Pain or tenderness, thought to be due
tion in epithelial cell size and a reduction in cell numbers mediated via to accumulation of fluid in the glandular ducts, may be a presenting
apoptosis (p. 26). Gradually, the breast tissue reverts to its resting state. feature. Histological changes are fibrosis and subsequent hyalinization.
If another pregnancy occurs, the resting glandular tissue is reactivated The aetiology in the majority of cases is idiopathic. Broadly speaking,
and the process outlined above recurs. Up to the age of 50 years, increas- causes may be either physiological, reflecting imbalances of sex hor-
ing amounts of elastic tissue tend to be laid down around vessels and mones in neonates, at puberty and in senescence, or pathological,
ducts (elastosis), and also in the stroma. Elastosis does not normally reflecting hypogonadal or hyperoestrogenic states. Acquired causes
continue into later life. include metabolic imbalances, endocrine and neoplastic conditions,
and drug-induced gynaecomastia. In the adult male, unilateral gynae-
Mammary stem cells Mammary stem cells (MaSCs) and distinct comastia should be investigated to exclude male breast cancer.
luminal progenitor cell types have been prospectively isolated from
adult mouse and human mammary tissue, implying the existence of an
INTERVENTIONAL ACCESS TO
epithelial differentiation hierarchy in the mammary gland. For further
reading on the role that MaSCs may play in the postnatal mammary THORACIC VISCERA


gland, see Rios et al (2014).
Thoracocentesis (pleural aspiration) Thoracocentesis or pleural
aspiration is an essential step in the assessment of pleural effusions. A
MALE BREAST
chest radiograph will confirm the location and extent of the effusion
and clinical examination will identify the best position for aspiration,
The male breast remains rudimentary throughout life. It is formed of the posterior mid-scapular line being a common site. The skin of the
small ducts (without lobules or alveoli) or solid cellular cords and a desired interspace is cleaned and anaesthetized, and the aspiration
little supporting fibroadipose tissue (Ellis et al 1993). Slight temporary needle is inserted at the lower margin of the interspace because the
enlargement may occur in the newborn, reflecting the influence of posterior intercostal vessels run mid-interspace. After appropriate local
maternal hormones, and again at puberty. The areola is well developed, analgesia has been applied, the needle is carefully advanced in a per-
although limited in area, and the nipple is relatively small. It is usually pendicular direction in the lower portion of the interspace until it enters
stated that the ducts do not extend beyond the areola in a male breast the pleural space. More complex or small effusions should be aspirated
but glandular tissue can be more extensive. under ultrasound guidance.
Gynaecomastia Needle thoracocentesis Needle thoracocentesis is performed
when a life-threatening tension pneumothorax is suspected. A needle
Gynaecomastia is a benign proliferation of subareolar breast tissue in is inserted into the second intercostal space in the mid-clavicular line
the male. It may be unilateral or bilateral and of varying severity (Simon on the side of the tension pneumothorax, with the patient in an erect


Chest wall and breast
952
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nOItCes
A position. A sudden escape of air is heard when the needle enters the
parietal pleura. A chest tube must be inserted after this procedure.
Chest drain insertion The insertion site for a chest drain is usually
the fifth intercostal space, just anterior to the mid-axillary line on the
affected side. A 2 cm horizontal incision is followed by blunt dissection
through the subcutaneous tissues to the top of the rib. The parietal
pleura is punctured with the tip of a clamp, and a gloved finger is
inserted into the pleural space to free up any adhesions. The chest drain
(thoracostomy tube) is then inserted into the pleural space and attached
to an underwater sealed container placed below the level of the lungs;
the water level rises and falls in the tube with ventilation.
Pericardiocentesis Pericardiocentesis is performed to aspirate a
pericardial effusion or, in an emergency, to decompress a cardiac tam-
Myoepithelial
Non-lactating cell Lactating ponade, where pressure from blood in the pericardial space prevents
(nulliparous)
the heart chambers from filling during the cardiac cycle, seriously
impairing cardiac output.
Pericardial puncture can be performed in either the fifth or sixth left
Lipid (milk fat) intercostal space near the sternum (to avoid the internal thoracic artery)
globule Basal lamina or at the left costoxiphoid angle. The needle is passed 1–2 cm to the
left of the costoxiphoid angle at 45° to the skin, and then up and
Secretory
protein backwards towards the tip of the scapula until it enters the pericardial
sac.
Myoepithelial
cell process Placement of electrocardiograph (ECG) leads
Available with the Gray’s Anatomy e-book
Ultrastructure of secretory cell Thoracotomy incisions
Available with the Gray’s Anatomy e-book
Sternotomy
Available with the Gray’s Anatomy e-book
Axillary thoracotomy
Available with the Gray’s Anatomy e-book
Thoracoscopic access
Available with the Gray’s Anatomy e-book
Bonus e-book images
B


Fig. 53.30 The microstructure of breast epithelium. A, Note that the Fig. 53.7 Pectus excavatum.
myoepithelial process is actually about half the relative size of that shown
in the lower diagram. B, The peripheral part of a lactating breast lobule Fig. 53.17 The internal thoracic vessels prepared for micro-
enclosed by a connective tissue septum (left). The alveoli are distended anastomosis beneath the third costal cartilage.
by milk secretion. Milk protein appears as eosinophilic material in the
lumen and milk fat as pale cytoplasmic vacuoles in the flattened alveolar Fig. 53.20 A,B, Pre- and post-embolization images after selective
epithelium. Intralobular connective tissue between the alveoli contains a catherization of the right eleventh posterior intercostal artery.
prominent lymphocytic infiltration, including plasma cells secreting IgA.
Fig. 53.26 A CT angiogram showing the deep inferior epigastric
artery and a perforator emerging from the rectus sheath.
KEY REFERENCES
Allen RJ, Treece P 1994 Deep inferior epigastric perforator flap for breast Hartrampf CR, Scheflan M, Black PW 1982 Breast reconstruction with a
reconstruction. Ann Plast Surg 32:32. transverse abdominal island flap. Plast Reconstr Surg 69:216–25.
Ellis H, Colborn GL, Skandalakis JE 1993 Surgical embryology and anatomy Simon BE, Hoffman S, Khan S 1973 Classification and surgical correction
of the breast and its related anatomic structures. Surg Clin North Am of gynaecomastia. Plast Reconstr Surg 51:48.
73:611–32. Tanis PJ, Nieweg OE, Valdes Olmos RA et al 2001 Anatomy and physiology
Fentiman IS 1993 Detection and Treatment of Early Breast Cancer. London: of lymphatic drainage of the breast from the perspective of sentinel
Martin Dunitz. node biopsy. J Am Coll Surg 192:399–409.
Fry WA 2000 Thoracic incisions. In: Shields TW, LoCicero III J, Ponn RB Tansini I 1906 Sopra il mio nuovo processo di amputazione della mamella.


(eds) General Thoracic Surgery, 5th ed. Philadelphia: Lippincott Riforma Medica (Palermo, Napoli) 12:757.
Williams & Wilkins; pp. 367–74.


Chest wall and breast
952.e1
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The 12-lead ECG provides three-dimensional information on the elec- muscles are divided, and subsequent access to the thorax is similar to
trical activity of the heart. The limb leads provide information about that used in the posterolateral approach. However, access is limited, and
the electrical activity in the frontal plane. They are placed on the left may be improved by dividing costal cartilages.
and right wrists and the left foot; the right foot acts as a neutral ground-
ing point. The chest leads provide information about the electrical ‘Clam shell’ The transverse thoracosternotomy is known as the ‘clam
activity in the horizontal plane and are placed as follows: V1, right shell’ incision. It provides excellent exposure to both sides of the chest
fourth intercostal space, parasternal position; V2, left fourth intercostal and is therefore used in bilateral lung transplantation and in lung
space, parasternal position; V3, midpoint of V2 and V4 on the left; V4, volume reduction surgery with bilateral lung resections. The patient is
fifth intercostal space, mid-clavicular line on the left; V5, fifth intercostal placed in the supine position with a roll vertically along the upper
space, anterior axillary line on the left; and V6, fifth intercostal space, thoracic spine. Bilateral anterolateral incisions are made in the
mid-axillary line on the left. inframammary fold, and the sternum is transected. This allows the
upper portion of the thorax to be displaced upwards with a rib-spreader;
Thoracotomy incisions may be posterolateral or anterolateral, or involve hence the name ‘clam shell’. The main disadvantage of the clam shell
a transverse thoracosternotomy. procedure is the need to transect the sternum; even after careful repair
with sternal wires, there is a risk of sternal instability.
Posterolateral incision A posterolateral incision is most commonly
used in thoracic surgery for unilateral pulmonary resections, bullec- Sternotomy is commonly needed in cardiac surgery. The patient is
tomy, unilateral lung volume reduction surgery, chest wall resection and placed in the supine position with both arms extended by the side. A


oesophageal surgery (Fry 2000). The patient is placed in a lateral decu- vertical incision is made in the midline from the suprasternal notch to
bitus position with adequate support of the elbow, axilla and knee with a point just below the xiphoid process; the tissues around the manu-
padding. The standard approach is via an incision from the anterior brium and the xiphoid process are mobilized; and the pectoral fascia
axillary line, which curves about 4 cm below the tip of the scapula and in the midline is incised. The sternum is split and its two edges retracted;
then vertically between the posterior midline and medial edge of the it is subsequently closed using interosseous wire sutures.
scapula. The incision is usually extended to the level of the spine of the
scapula. Overall, the incision forms an S-shape in the fifth intercostal The patient is placed in the lateral decubitus position, with arms
space. The sixth or seventh intercostal space is used in oesophageal abducted at 90° and supported on an arm rest. The incision is based
surgery. along the desired intercostal space; for upper thoracic lesions, this is
The lower portions of trapezius and latissimus dorsi are divided. the second or third space. Latissimus dorsi is elevated and retracted,
Serratus anterior is retracted, and may be divided in a high thoracotomy. whereas serratus anterior is divided in the direction of its fibres. The
The costal muscle and pleura are dissected along the inferior margin of anterior aspect of serratus anterior is divided to expose the intercostal
the intercostal space to avoid damaging the neurovascular bundle. A muscles, which are divided in turn. The overall size of the incision is
small section of rib is removed at the costovertebral angle to reduce the limited and it provides good access to the upper thorax. Postoperative
risk of fracture, particularly in patients older than 40 years. This tech- pain is less than with some other approaches, but the long thoracic
nique provides good access to the thoracic contents; the main problem nerve (nerve of Bell) may be damaged if serratus anterior is divided too
is postoperative pain as a consequence of intraoperative musculoskel- posteriorly.
etal traction.


Occasionally, video-assisted thoracoscopic surgery is required to assess
Anterolateral incision The patient is placed in the supine position, with the mediastinum. The thoracoscope is usually introduced via the fifth
the arms by the sides. A roll is placed vertically under the back and hips intercostal space in the mid-clavicular line, with additional ports at the
in order to raise the operative side by approximately 45°. The incision third and sixth intercostal spaces to assess the anterior mediastinum.
is from the mid-axillary line over the fifth intercostal space along the To assess the posterior mediastinum, the thoracoscope is inserted into
inframammary fold, and curves upwards parasternally. The pectoral the seventh intercostal space in the mid-clavicular line.


Chest wall and breast
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REFERENCES
Allen RJ, Treece P 1994 Deep inferior epigastric perforator flap for breast Neligan PC, Gullane PJ, Vesely M et al 2007 The internal mammary artery
reconstruction. Ann Plast Surg 32:32. perforator flap: new variation on an old theme. Plast Reconstr Surg
Arnez ZM, Bajec J, Bardsley AF et al 1991 Experience with 50 free TRAM flap 119:891–3.
breast reconstructions. Plas Reconstr Surg 87:470. Ninković M, Anderl H, Hefel L et al 1995 Internal mammary vessels: a reli-
Bakamjian VY, Long M, Rigg B 1971 Experience with the medially based able recipient system for free flaps in breast reconstruction. Br J Plas Surg
deltopectoral flap in reconstructive surgery of the head and neck. Br J 48:533–9.
Plast Surg 24:174. Nuss D, Kelly RE, Croitoru DP et al 1988 A 10 year review of a minimally
Blondeel PN, Vanderstraeten GG, Monstrey SJ et al 1997 The donor site invasive technique for the correction of pectus excavatum. J Paediatr
morbidity of free DIEP flaps and free TRAM flaps for breast reconstruc- Surg 33:545–52.
tion. Br J Plas Surg 50:322. Papp C, Zanon E, McCraw J 1988 Breast volume replacement using the
Bostwick J, Vasconez LO, Jurkiewicz MJ 1977 Breast reconstruction after a de-epithelialised latissimus dorsi myocutaneous flap. Eur J Plast Surg
radical mastectomy. Plas Reconstr Surg 61:682. 11:120.
Delay E, Gounot N, Bouillot A et al 1998 Autologous latissimus breast Park HJ, Lee SY, Lee CS et al 2004 The Nuss procedure for pectus excavatum:
reconstruction: a 3 year clinical experience with 100 patients. Plas evolution of techniques and early results on 322 patients. Ann Thorac


Reconstr Surg 102:1461. Surg 77:289.
Ellis H, Colborn GL, Skandalakis JE 1993 Surgical embryology and anatomy Park MC, Lee JH, Chung J et al 2003 Use of internal mammary vessel per-
of the breast and its related anatomic structures. Surg Clin North Am forator as a recipient vessel for free TRAM breast reconstruction. Ann
73:611–32. Plast Surg 50:132–7.
Fentiman IS 1993 Detection and Treatment of Early Breast Cancer. London: Parrett BM, Caterson SA, Tobias AM et al 2008 The rib-sparing technique
Martin Dunitz. for internal mammary vessel exposure in microsurgical breast recon-
struction. Ann Plast Surg 60:241–3.
Fry WA 2000 Thoracic incisions. In: Shields TW, LoCicero III J, Ponn RB
(eds) General Thoracic Surgery, 5th ed. Philadelphia: Lippincott Raab N, Holm-Muehlbauer C, Ninkovic M 2009 Free superficial epigastric
Williams & Wilkins; pp. 367–74. artery flap for aesthetic correction of mild pectus excavatum. Plast
Reconstr Surg; 123:209e–11e.
Grotting JC, Urist MM, Maddox WA et al 1989 Conventional TRAM flap
versus free microsurgical TRAM flap for immediate breast reconstruc- Ravitch MM 1955 The operative treatment of pectus excavatum. J S C Med
tion. Plas Reconstr Surg 83:828. Assoc 51:244–9.
Hartrampf CR, Scheflan M, Black PW 1982 Breast reconstruction with a Rios AC, Fu NY, Lindeman GJ et al 2014 In situ identification of bipotent
transverse abdominal island flap. Plast Reconstr Surg 69:216–25. stem cells in the mammary gland. Nature 506:322–7.
Hokin JA, Silfverskiold KL 1987 Breast reconstruction without an implant: Schneider WJ, Hill HL, Brown RG 1978 Latissimus dorsi myocutaneous flap
results and complications using an extended latissimus dorsi flap. Plast for breast reconstruction. Br J Plas Surg 30:277.


Reconstr Surg 79:58–66. Schusterman MA, Kroll SS, Miller MJ et al 1994 The free transverse rectus
Holmstrom H 1979 The free abdominoplasty flap and its use in breast abdominis musculocutaneous flap for breast reconstruction: one
reconstruction. Scand J Plast Reconstr Surg 13:423. center’s experience with 211 consecutive cases. Ann Plast Surg 32:234.
Ladak A, Tubbs RS, Spinner RJ 2014 Mapping sensory nerve communica- Serletti JM, Moran SL 2000 Microvascular reconstruction of the breast.
tions between peripheral nerve territories. Clin Anat 27:681–90. Semin Surg Oncol 19:264–71.
Malata CM, Moses M, Mickute Z et al 2011 Tips for successful microvascular Simon BE, Hoffman S, Khan S 1973 Classification and surgical correction
abdominal flap breast reconstruction utilizing the ‘total rib preservation’ of gynaecomastia. Plast Reconstr Surg 51:48.
technique for internal mammary vessel exposure. Ann Plast Surg 66: Snosek M, Tubbs RS, Loukas M 2014 Sternalis muscle, what every anatomist
36–42. and clinician should know. Clin Anat 27:866–84.
Masson JK, Payne WS, Gonzalez JB 1970 Pectus excavatum: use of preformed Swanson GP, Rynearson K, Symmonds, R 2002 Significance of margins of
prosthesis for correction in the adult. Case report. Plast Reconstr Surg excision on breast cancer recurrence. Am J Clin Oncol 25:438–41.
46:399–402. Tanis PJ, Nieweg OE, Valdes Olmos RA et al 2001 Anatomy and physiology
Maxwell GP, McGibbon BM, Hoopes JE 1979 Vascular considerations in the of lymphatic drainage of the breast from the perspective of sentinel
use of a latissimus dorsi myocutaneous flap after a mastectomy with an node biopsy. J Am Coll Surg 192:399–409.
axillary dissection. Plas Reconstr Surg 64:771. Tansini I 1906 Sopra il mio nuovo processo di amputazione della mamella.


McCraw JB, Dibbell DG, Carraway JH 1977 Clinical definition of independ- Riforma Medica (Palermo, Napoli) 12:757.
ent myocutaneous vascular territories. Plas Reconstr Surg 60:341.
Munhoz AM, Ishida LH, Montag E et al 2004 Perforator flap breast recon-
struction using the internal mammary perforator branches as a recipient
site: an anatomical and clinical analysis. Plast Reconstr Surg 114:62–8.


SUBSECTION: Lungs and diaphragm
CHAPTER
54
Pleura, lungs, trachea and bronchi
The lungs are the essential organs of respiration and are responsible mediastinal space. Cardiac asymmetry dictates that the left pleural
for the uptake of oxygen into the blood and the removal of carbon cavity is smaller, although it may extend more inferiorly in the mid-
dioxide. The functional design of the thorax facilitates this complex axillary line in response to left hemidiaphragmatic disposition. Transu-
process. Acting together, the muscles of respiration and the diaphragm dates accumulate earlier within, and have a preference for, the larger
increase the intrathoracic volume, creating a negative pressure within right pleural cavity.
the pleural space that causes lung expansion. The resultant reduction The folded portions of the pleura at its reflection sites (retrosternal,
in intra-alveolar pressure prompts the conduction of air through the interlobar fissures and the azygo-oesophageal recess) are the only
upper respiratory tract, trachea, bronchi and bronchioles, and finally aspects of normal pleura that can be visualized radiologically. Demon-
into the alveoli, where gaseous exchange occurs. The respiratory move- stration of significant pleural shadowing in any other region usually
ments do not clear the lung of its gas with each breath; the presence of implies pathological pleural abnormality. At direct inspection of the
a large residual volume of gas minimizes the degree to which each new pleural cavity, either during surgery or thoracoscopy, both parietal and
breath can affect the composition of gas in diffusion exchange with the visceral pleura appear translucent; the underlying thoracic muscles and
blood (Lambertsen 1980). Besides efficient oxygen diffusion from alve- blood vessels are visible beneath the parietal pleura, and the lung and
olar air to blood, the lungs must also provide an inefficient carbon subpleural vascular network are visible beneath the visceral pleura,
dioxide transfer, thus maintaining a stable carbon dioxide blood and rendering the latter grey and variegated.
tissue pressure, grossly higher (about 40 mmHg) than that in the
atmosphere. Maintenance of critical homeostasis for carbon dioxide
pressure is of greater importance than precise control of oxygen because PARIETAL PLEURA
so many essential electrical and metabolic functions depend on the


hydrogen ion concentration [H+] of the fluids in which these functions Although it is a continuous structure, different regions of parietal pleura
are carried out. are customarily distinguished by name. Thus the costovertebral pleura
The process of breathing exposes the lung to noxious agents, includ- lines the internal surface of the thoracic wall and the vertebral bodies,
ing gases, dust particles, bacteria and viruses, and to dehydration and the diaphragmatic pleura lies on the thoracic muscular surface of the
freezing. The mucous barrier (including its cellular and immunoglobu- diaphragm, the cervical pleura (pleural dome) covers the pulmonary
lin factors), the mucociliary escalator, branching pattern of the airways apices, and the mediastinal pleura is applied to the structures between
and the cough reflex are all anatomical defences against these insults. the lungs.
Studies of trends of particle deposition in children and young adults
have shown that pulmonary deposition fractions are highest in infants Costovertebral pleura
who are at greatest risk from exposure to airborne particulate matter
(Asgharian et al 2004). Respiratory function may be compromised The costovertebral pleura lines the sternum, ribs, transversus thoracis,
either by anatomical defects such as chest wall abnormalities or by intercostal muscles and the sides of the vertebral bodies; normally, it is
paralysis of respiratory muscles. Similarly, ultrastructural abnormalities, easily separated from these structures. External to the pleura is a thin
such as ciliary dysfunction (as seen in Kartagener’s syndrome), lead to layer of loose connective tissue, the endothoracic fascia, analogous to
recurrent respiratory infections and airway damage. the transversalis fascia of the abdominal wall. Anteriorly, the costal
pleura begins posterior to the sternum, where it is continuous with the
mediastinal pleura along a line extending from posterior to the sterno-
PLEURA clavicular joint inferomedially to the midline posterior to the sternal
angle. From here, the right and left costal pleurae descend in contact
Each lung is covered by pleura, a serous membrane arranged as a closed with each other to the level of the fourth costal cartilages and then


invaginated sac. The visceral (pulmonary) pleura adheres closely to the diverge. On the right side, the line descends to reach the posterior aspect
lung surface and follows the interlobar fissures, eventually ensheathing of the xiphisternal joint, while on the left the line diverges laterally and
each pulmonary lobe. The visceral pleura continues over the hila as the descends at a distance of 2–2.5 mm from the sternal margin to the sixth
parietal pleura, covering the mediastinal organs, most of the diaphragm costal cartilage, forming the cardiac notch. On each side, the costal
and the corresponding half of the thoracic wall. pleura sweeps laterally, lining the internal surfaces of the costal carti-
The pleural cavity represents the potential space between the two lages, ribs, transversus thoracis and intercostal muscles. Posteriorly, it
pleura and incorporates an intervening pellicle of fluid that allows close passes over the sympathetic trunk and its branches to reach the sides of
sliding contact between the two layers during all phases of respiration. the vertebral bodies, where it is again continuous with the mediastinal
This liquid pellicle has a high daily turnover: fluid is produced at 0.01– pleura. Superior to the first rib, the costovertebral pleura is continuous
0.02 ml/kg/h and is continuously absorbed to maintain a pleural fluid with the cervical pleura; inferiorly, it becomes continuous with the
level of 0.1–0.2 ml/kg. Fluid movement and absorption are supported diaphragmatic pleura along a line that differs slightly on the two sides.
by a balance between plasmatic and pleural (hydrostatic and oncotic) On the right, this line of costodiaphragmatic reflection begins posterior
pressures and thoracic lymphatic drainage. Pleural effusions occur when to the xiphoid process, passes posterior to the seventh costal cartilage
the mechanisms that normally resorb the fluid pellicle are destabilized. to reach the eighth rib in the mid-clavicular line and the tenth rib in
The negative pressure developed in the pleural cavity is the result of the mid-axillary line, then ascends slightly to cross the twelfth rib level


the opposing outward pull of the chest wall and the inward elastic recoil with the upper border of the twelfth thoracic spine. On the left, the line
of the lung. Any change in the elasticity of these structures or accumula- initially follows the ascending part of the sixth costal cartilage but then
tion of fluid or air will alter respiratory activity either regionally or follows a course similar to that on the right, although it may be slightly
globally. Inter-regional disparities in ventilation normally exist as a lower.
result of local differences in thoracic expansion and position-related,
Diaphragmatic pleura
gravity-dependent gradients in pleural pressure, and are reflected as
regional inequalities in gas exchange.
The right and left pleural sacs constitute separate compartments and The diaphragmatic pleura is a thin, tightly adherent layer that covers
are contiguous only posterior to the upper half of the sternal body. They most of the superior surface of the diaphragm. It is continuous with
come close to each other posterior to the oesophagus at the mid- the costal pleura and medially with the mediastinal pleura along the
thoracic level and are widely separate between, where they enclose the line of attachment of the pericardium to the diaphragm. 953


Pleura, lungs, trachea and bronchi
954
7
noitces
Internal thoracic vein Sternum
Internal thoracic artery
Sternal reflection of pleura
First rib
Second rib Brachiocephalic trunk
Superior vena cava
Scalenus anterior
Phrenic nerve
Left common carotid artery
Trachea
Left phrenic nerve
Vagus nerve
Left vagus nerve
Right recurrent
laryngeal nerve Left recurrent laryngeal nerve
Ansa subclavia Left subclavian artery
Scalenus medius
Vertebral artery
Oesophagus
Thoracic duct
First thoracic ventral ramus
First intercostal nerve Superior intercostal artery
Inferior cervical ganglion
Second thoracic
ventral ramus
Fig. 54.1 Structures related to the cervical pleura, as seen from below.
Cervical pleura the lung and along a line descending from this, which marks the attach-
ment of the pulmonary ligament (Figs 54.2–54.3).
The cervical pleura is the continuation of the costovertebral pleura over
the pulmonary apex, looking as if it is moulded by the latter (see Fig.
INFERIOR PULMONARY LIGAMENTS
51.1). It ascends medially from the internal border of the first rib to the
apex of the lung, as high as the inferior edge of the neck of the first rib,
The mediastinal pleura extends as a double layer, the pulmonary liga-
and then descends lateral to the trachea to become the mediastinal
ment, inferior to the hilum, from the lateral surface of the oesophagus
pleura. As a result of the obliquity of the first rib, the cervical pleura
to the mediastinal surface of the lung, where it is continuous with the
extends 3–4 cm superior to the first costal cartilage, but not superior to
visceral pleura (see Figs 54.2B–54.3B). It is continuous superiorly with
the neck of the first rib. The cervical pleura is strengthened by a fascial
the pleura around the hilar structures, and inferiorly it ends in a free
supra pleural membrane that is attached anteriorly to the internal border
sickle-shaped contour.


of the first rib and posteriorly to the anterior border of the transverse
process of the seventh cervical vertebra. It contains a few muscular fibres,
which spread from the scaleni. Scalenus minimus extends from the PLEURAL RECESSES
anterior border of the transverse process of the seventh cervical vertebra
to the inner border of the first rib behind its subclavian groove, and also
The pleura extends considerably beyond the inferior border of the lung
spreads into the pleural dome, which it therefore tenses; it has been
but not as far as the attachment of the diaphragm; therefore, the dia-
suggested that the suprapleural membrane is the tendon of sca lenus
phragm is in contact with the costal cartilages and intercostal muscles
medius. The cervical pleura and the pulmonary apex reach the level of
below the line of pleural reflection from the thoracic wall to the dia-
the seventh cervical spine approximately 2.5 cm from the midline. Their
phragm. In quiet inspiration, the inferior margin of the lung does not
surface projection is a curved line from the sternoc lavicular joint to the
reach this reflection and the costal and diaphragmatic pleurae are sepa-
junction of the medial and middle thirds of the clavicle, its summit
rated merely by a narrow slit, the costodiaphragmatic recess; the lower
being 2.5 cm superior to the clavicle (see Fig. 51.4). The subclavian
limit of the lung is normally 5 cm above the lower pleural limit. A
artery ascends laterally in a furrow posterior to the summit of the cervical
similar costomediastinal recess exists posterior to the sternum and the
pleura (Fig. 54.1). The dome is related to the supraclavicular part of the
costal cartilages, where the thin anterior margin of the lung falls short
brachial plexus, the stellate ganglion and the vertebral vessels.
of the line of pleural reflection. The extent of this recess, the anterior
costomediastinal line of pleural reflection, and the position of the
Mediastinal pleura
anterior margin of the lung all exhibit individual variation.
The pleural recesses allow the proportionate inspiratory expansion


The mediastinal pleura represents the lateral boundary of the mediasti- of the lungs, admitting the supplementary volume with minimal fric-
num and forms a continuous coat above the hilum of the lung from tion. The same pellicle of fluid within the recesses separates the parietal
the sternum to the vertebral column. On the right, it covers the right costal and diaphragmatic pleura during expiration, or the parietal
brachiocephalic vein, upper part of the superior vena cava, terminal part pleura from the intervening visceral pleura during inspiration. Pleural
of the azygos vein, right phrenic and vagus nerves, trachea and oesopha- adhesions and air or fluid accumulation limit this mechanism to a vari-
gus. On the left, it covers the aortic arch, left phrenic and vagus nerves, able degree.
left brachiocephalic and superior intercostal veins, left common carotid The inferior border of the costodiaphragmatic recess is an important
and subclavian arteries, thoracic duct and oesophagus. At the hilum of consideration in the surgical posterior approach to the kidney. Usually,
the lung, it turns laterally to form a tube that encloses the hilar struc- the pleura crosses the twelfth rib at the lateral border of erector spinae,
tures and is continuous with the pulmonary pleura. so that the medial region of the kidney is above the pleural reflection.
The eleventh rib may be mistaken for the twelfth in palpation (some-
times the latter does not project beyond muscle) and an incision pro-
VISCERAL PLEURA longed to this level will open the pleura. Whether the lowest palpable
rib is the eleventh or twelfth can be ascertained by counting from the
The pulmonary pleura is inseparably adherent to the lung over all its second rib (identified at its junction with the sternal angle) or by
surfaces, including those in the fissures, except at the root or hilum of ultrasound.


Pleura
955
45
retPahc
A B
Apex
Superior lobe
Oblique fissure Right superior
lobar bronchus
Right main
Superior lobe,
Right pulmonary artery bronchus
costal suface
Middle and right
inferior lobar
Anterior border bronchi
Inferior
Right pulmonary veins tracheobronchial node
Cardiac impression Parietal pleura,
mediastinal part
Horizontal fissure
Inferior lobe
Pulmonary
Costal surface Middle lobe ligament
Inferior lobe, Diaphragmatic
costal surface surface;
base of lung
Oblique fissure
Inferior border
Inferior border
Fig. 54.2 The right lung. A, Lateral surface. B, Medial surface. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy,
15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
A B
Apex
Superior lobe, Oblique fissure
costal surface
Left pulmonary artery
Oblique fissure
Left superior Parietal pleura,
pulmonary vein mediastinal part
Left main bronchus
Anterior border
Left inferior
pulmonary
vein Anterior border
Inferior lobe,
costal surface
Pulmonary Tracheobronchial
ligament nodes
Cardiac impression
Cardiac notch
Diaphragmatic
surface; Cardiac notch
base of lung
Lingula
Inferior border
Lingula
Oblique fissure
Fig. 54.3 The left lung. A, Lateral surface. B, Medial surface. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th
ed, Elsevier, Urban & Fischer. Copyright 2013.)
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE and intercostal chains posteriorly, while that from the diaphragmatic
pleura drains into the mediastinal, retrosternal and coeliac axis
The parietal and visceral pleurae are developed from somatopleural nodes.
and splanchnopleural layers of the lateral plate mesoderm, respec- The visceral pleura forms an integral part of the lung and, accord-


tively; consequently, the parietal pleura has a somatic arterial supply. ingly, its arterial supply and venous drainage are provided by the
The costovertebral pleura is supplied by branches of the intercostal bronchial vessels. The bronchial arteries at the hilum form a circle, sur-
and internal thoracic arteries; the mediastinal pleura by branches rounding the principal bronchus; pleural branches from this anulus
from the bronchial, upper diaphragmatic, internal thoracic and medi- supply the visceral pleura facing the mediastinum, the interlobar and
astinal arteries; the cervical pleura by branches from the subclavian apical surfaces, and part of the diaphragmatic surface. The visceral
artery; and the diaphragmatic pleura by the superficial part of the dia- pleura is drained by pulmonary veins, apart from an area around the
phragmatic microcirculation. The veins join the thoracic wall veins, hilum that drains into bronchial veins. The lymphatic drainage of the
eventually draining into the superior vena cava. Lymph from the cos- visceral pleura is to the deep pulmonary plexus within the interlobar
tovertebral pleura drains into the internal thoracic chain anteriorly and peribronchial spaces.


Pleura, lungs, trachea and bronchi
956
7
noitces
INNERVATION The adult right lung usually weighs 625 g, and the left 565 g, but
the range of wet weights is considerable, not least because it reflects the
The costal and peripheral diaphragmatic parietal pleurae are innervated amount of blood or serous fluid contained within the lungs when
by intercostal nerves. The mediastinal and central diaphragmatic pari- weighed. In proportion to body stature, the lungs are heavier in men
etal pleurae are innervated by the phrenic nerves. Irritation of the than in women, and boys have bigger lungs than girls (Thurlbeck 1982).
former results in pain that is referred to the appropriate part of the Lung volumes in children vary significantly according to race (Sylvester
thoracic or abdominal wall, whereas irritation of the central diaphrag- et al 2005), and lung volume, air volume and pulmonary tissue volume
matic pleura causes pain that is referred to the lower neck and shoulder all increase linearly with body length (Rao et al 2010). Pulmonary
tip, i.e. to the C3 and 4 dermatomes. Visceral afferents travel along the agenesis is a rare congenital abnormality in which pulmonary vessels,
bronchial vessels with the autonomic fibres. bronchi and lung parenchyma are undeveloped; it is associated with
congenital heart disease (Nabati et al 2013).
PNEUMOTHORAX Pulmonary surface features
Any breach of the chest wall and parietal pleura or visceral pleura leads Each lung has an apex, base, three borders and two surfaces, roughly
to the accumulation of air within the pleural cavity (pneumothorax). resembling a halved cone (see Figs 54.2–54.3).
Fluid (hydrothorax), blood (haemothorax) and, rarely, lymph (chylo-
thorax) can also accumulate in this space. Pneumothoraces may occur Apex
spontaneously (rupture of emphysematous bullae, or subpleural ‘blebs’ The apex, the rounded upper extremity, extends above the superior


typically in tall, asthenic males) or following rib or penetrating trauma. thoracic aperture where it contacts the cervical pleura, and is covered
Significant air in the pleural space is visible on a chest radiograph in turn by the suprapleural membrane. As a consequence of the obliq-
because this condition leads to various degrees of pulmonary collapse; uity of the aperture, the apex rises 3–4 cm above the level of the first
there is separation of the parietal and visceral pleurae and an absence costal cartilage. The summit of the apex is level posteriorly with the
of peripheral pulmonary vascular markings in the corresponding area. neck of the first rib and lies 2.5 cm above the junction of the mid and
Occasionally, a valve-like effect occurs, so that air enters the pleural medial thirds of the clavicle, therefore within the root of the neck (see
space during inspiration but cannot escape in expiration. This may Fig. 29.18). It has been claimed that, because the apex does not rise
result in a ‘tension pneumothorax’, which can be life-threatening and above the neck of the first rib, it is really intrathoracic, and that it is the
should be suspected whenever there are unilateral decreased breath anterior surface that ascends highest in inspiration. The subclavian
sounds and hyper-resonance on percussion (due to collapse of the artery arches superolaterally over the suprapleural membrane and
lung), hypotension, jugular venous distension and contralateral tra- grooves the anterior surface of the apex near its summit, separating it
cheal deviation (due to mediastinal shift). A tension pneumothorax from scalenus anterior. The cervicothoracic (stellate) sympathetic gan-
requires immediate decompression with intercostal drainage, preceded glion, ventral ramus of the first thoracic spinal nerve and superior
by, if in extremis, a wide-bore needle in the second intercostal space intercostal artery all lie posterior to the apex. Scalenus medius is lateral
anteriorly in the mid-clavicular line. Fluid collection in the pleural and the brachiocephalic trunk, right brachiocephalic vein and trachea


space may be due to congestive cardiac failure, hypoalbuminaemia or are adjacent to the medial surface of the apex of the right lung. The left
inflammatory, infective or neoplastic conditions. An incipient pleural subclavian artery and left brachiocephalic vein are adjacent to the
effusion causes obliteration of the costophrenic angle, where a lateral medial surface of the apex of the left lung.
fluid meniscus is often visible from a non-loculated effusion on a
frontal chest radiograph. Drainage of the fluid and subsequent analysis Base
are required for diagnostic purposes. Where there is a collection of pus The basal surface is semilunar and concave, moulded on the superior
(empyema) or blood, pleural drainage is essential for therapeutic pur- surface of the diaphragm, which separates each lung from the corre-
poses. Ultrasonography is useful in assessing the size and characteristics sponding lobe of the liver, and the left lung from the gastric fundus and
of an effusion, such as the presence of loculation and debris. It may spleen. Since the diaphragm extends higher on the right than on the
even demonstrate underlying consolidated lung. Computed tomogra- left, the concavity is deeper on the base of the right lung. Posterolater-
phy (CT) is utilized to assess the underlying lung parenchyma, endo- ally, the base has a sharp margin that projects a little into the costodia-
bronchium and mediastinal lymph nodes. phragmatic recess.
Costal surface
MICROSTRUCTURE
The costal surface of the lung is smooth and convex, and its shape is
adapted to that of the thoracic wall, which is vertically deeper posteri-
The moist, smooth pleural surface consists of a single layer of flat meso- orly. It is in contact with the costal pleura; in specimens that have been
thelial (serosal) cells separated from an underlying lamina propria of preserved in situ, this surface exhibits grooves that correspond with the
loose connective tissue by a basal lamina. Ultrastructurally, pleural and overlying ribs, a situation similar to the hyperinflated lungs of asthma
peritoneal mesothelial cells are similar in having a highly folded basal patients.
plasma membrane, in that their adjacent cell surfaces interdigitate and


are joined by desmosomes, and in that their luminal surfaces bear Medial surface
numerous microvilli and some cilia. Cytoplasmic pinocytotic vesicles The medial surface has posterior vertebral and anterior mediastinal
are common. The connective tissue covers the entire pulmonary surface; parts. The vertebral part lies in contact with the sides of the thoracic
it extends from the hilum along the conducting tubes and blood vessels vertebrae and intervertebral discs, posterior intercostal vessels and
within the substance of the lung and divides the lung into numerous splanchnic nerves. The mediastinal area is deeply concave because it is
small polyhedral lobules, each of which receives a terminal bronchiole adapted to the heart at the cardiac impression, which is much larger
and arteriole, venules, lymphatics and nerves. Lobules vary in size; the and deeper on the left lung where the heart projects more to the left
superficial ones are the largest, visible as polygonal areas 5–15 mm of the median plane. Posterosuperior to this concavity is the some-
across. what triangular hilum, where various structures enter or leave the
lung, collectively surrounded by a sleeve of pleura that also extends
below the hilum and behind the cardiac impression as the pulmonary
LUNGS
ligament.
The lungs are the essential organs of respiration. They are situated on Other impressions on the lung surface
either side of the heart and other mediastinal structures, and occupy In addition to these pulmonary features, cadaveric lungs that have been
most of the thoracic cavity. Each lung is free in its pleural cavity, except preserved in situ can show a number of other impressions that indicate
at the hilum and pulmonary ligament, where it is attached to the medi- their relations with surrounding structures (see Figs 54.2B–54.3B). All
astinum. When removed from the thorax, a fresh normal lung is spongy, these impressions reflect the intimate relationships of the lungs with
can float in water, and crepitates when handled because of the air within the adjacent mediastinal structures and offer a good perspective on
its alveoli. It is also highly elastic and so retracts on removal from the surgical approaches, either from the anterior or posterior aspect of the


thorax. Its surface is smooth and shiny, and is divided by fine, dark lines corresponding pleural cavity.
into numerous small polyhedral domains, each crossed by numerous On the right lung, the cardiac impression is related to the anterior
finer lines, indicating the areas of contact between its most peripheral surface of the right auricle, the anterolateral surface of the right
lobules and the pleural surface. atrium and partially to the anterior surface of the right ventricle. The


lungs
957
45
retPahc
impression ascends anterior to the hilum as a wide groove for the of the costal surface, the inferior part of the anterior border and the
superior vena cava and the terminal portion of the right brachiocephalic anterior part of the base of the lung. The azygos vein may sometimes
vein. Posteriorly, this groove is joined by a deep sulcus that arches course in a more lateral position, within a four-layered pleural septum
forwards above the hilum and is occupied by the azygos vein. The right within the superior lobe, creating an ‘azygos lobe’. This is not a true
side of the oesophagus makes a shallow vertical groove behind the lobe, but a separated portion of the superior lobe that lacks its own
hilum and the pulmonary ligament. Towards the diaphragm it inclines bronchi, arteries or veins. The condition represents an incidental finding
left and leaves the right lung, and therefore does not reach the lower on chest radiographs or CT scans, with no associated morbidity; it may
limit of this surface. Posteroinferiorly, the cardiac impression is conflu- be confused with a pulmonary nodule, and loculated effusions in the
ent with a short, wide groove adapted to the inferior vena cava. Between fissure may appear. Accessory fissures may separate either the medial
the apex and the azygos groove, the trachea and right vagus are close to basal segment (Twining’s line) or the superior segment from the
the lung but do not mark it. remainder of the inferior lobe. Incomplete separation of the lobes and
On the left lung, the cardiac impression is related to the anterolateral identification of the completeness of the fissures are important prior to
surface of the left ventricle and auricle (see Fig. 54.3B). The anterior lobectomy because individuals with incomplete fissures are more prone
infundibular surface and adjoining part of the right ventricle are related to develop postoperative air leaks and may require further procedures,
to the lung as it ascends in front of the hilum to accommodate the such as stapling and pericardial sleeves.
pulmonary trunk. A large groove arches over the hilum, and descends
behind it and the pulmonary ligament, corresponding to the aortic arch Left lung


and descending aorta. From its summit, a narrower groove ascends to
the apex for the left subclavian artery. Posterior to this, and superior to
The left lung is divided into superior and inferior lobes by its oblique
the aortic groove, the lung is in contact with the thoracic duct and
fissure, which extends from the costal to the medial pulmonary surfaces,
oesophagus. Anterior to the subclavian groove there is a faint linear
superior and inferior to the hilum (see Fig. 54.3). Superficially, this
depression for the left brachiocephalic vein. Inferiorly, the oesophagus
fissure begins on the medial surface at the posterosuperior part of the
may mould the surface anterior to the lower end of the pulmonary
hilum, ascends obliquely and posteriorly to cross the posterior border
ligament.
of the lung 6 cm below the apex, then descends anteriorly across the
costal surface, to reach the inferior border almost at its anterior end. It
Pulmonary borders finally ascends on the medial surface to the inferior part of the hilum.
At the posterior border of the lung, the fissure usually lies opposite a
The inferior border is thin and sharp where it separates the base from surface point 2 cm lateral to the midline between the spines of the third
the costal surface and extends into the costodiaphragmatic recess, and and fourth thoracic vertebrae, but it may be superior or inferior to this
more rounded medially where it divides the base from the mediastinal level. Traced around the chest, the fissure reaches the fifth intercostal
surface. It corresponds, in quiet respiration, to a line drawn from the space (at or near the mid-axillary line) and follows this to intersect the
most inferior point of the anterior border that passes to the sixth rib at inferior border of the lung, close or just inferior to the sixth costochon-
about the mid-clavicular line, then to the eighth rib in the mid-axillary dral junction (7.5 cm from the midline). The left oblique fissure is
line (usually 10 cm above the costal margin), and then continues pos- usually more vertical than the right, and is indicated approximately by


teromedially and slightly superiorly to a point 2 cm lateral to the tenth the medial border of the scapula with the fully abducted arm. A left
thoracic spine (see Fig. 51.5). The diaphragm rises more superiorly on horizontal fissure is a normal, occasional variant.
the right to accommodate the liver, and so the right lung is vertically The superior lobe lies anterosuperior to the oblique fissure and
shorter (by approximately 2.5 cm) than the left. However, cardiac asym- includes the apex, anterior border, much of the costal and most of the
metry means that the right lung is broader, and has a greater capacity medial surfaces of the lung. A small process, the lingula, is usually
and weight than the left. The posterior border separates the costal present at the lower end of the cardiac notch. The larger inferior lobe
surface from the mediastinal surface, and corresponds to the heads of lies behind and below the fissure, and contributes almost the whole of
the ribs. It has no recognizable markings and is really a rounded junc- the base, much of the costal surface and most of the posterior border
tion of costal and vertebral (medial) surfaces. The thin, sharp, anterior of the left lung.
border overlaps the pericardium. On the right, it corresponds closely to Lung lobation, and the morphology of the tracheobronchial tree,
the costomediastinal line of pleural reflection, and is almost vertical. can predict the atrial situs.
On the left it approaches the same line above the fourth costal cartilage; In situs solitus, the right principal bronchus is short and eparterial
below this point, it shows a variable cardiac notch, the edge of which (its branch for the right upper lobe lies over the second branch of the
passes laterally for 3.5 cm before curving inferomedially to the sixth right pulmonary artery) and the left principal bronchus is longer and
costal cartilage 4 cm from the midline. It therefore does not reach the hyparterial (it courses underneath the left pulmonary artery). A bilobed
line of pleural reflection here (see Fig. 51.4) and so the pericardium is left lung and a trilobed right lung are typical in situs solitus. In situs


covered only by a double layer of pleura (area of superficial cardiac inversus, there is a mirror imaging of the disposition seen in situs
dullness). Surgical experience suggests that the line of pleural reflection, solitus. In situs ambiguus, the bronchi and lungs can display either a
the anterior pulmonary margin and the costomediastinal pleural recess bilateral right morphology with bilateral trilobed lungs and bilateral
are all variable. eparterial bronchi (heterotaxy syndrome: incomplete or inappropriate
lateralization of the thoracic and abdominal viscera, and asplenia) or
a bilateral left morphology with bilateral bilobed lungs and bilateral
PULMONARY FISSURES AND LOBES hyparterial bronchi (heterotaxy syndrome and polysplenia) (Van Praagh
et al 1992).
Right lung
Bronchopulmonary segments
The right lung is divided into superior, middle and inferior lobes by its
oblique (major) and horizontal (minor) fissures (see Fig. 54.2). The Each of the principal bronchi divides into lobar bronchi. Primary
superior, lengthier oblique fissure separates the inferior from the supe- branches of the right and left lobar bronchi are termed segmental
rior and middle lobes, and corresponds closely to the left oblique bronchi because each ramifies in a structurally separate, functionally
fissure, although it is less vertical, crossing the inferior border of the independent, unit of lung tissue called a bronchopulmonary segment
lung approximately 7.5 cm behind its anterior end. On the posterior (Figs 54.5–54.7).
border, it is either level with the spine of the fourth thoracic vertebra The main segments are named and numbered as shown in
or slightly lower. It descends across the fifth intercostal space and Table 54.1.
follows the sixth rib to the sixth costochondral junction. The shorter Each segment is surrounded by connective tissue that is continuous
horizontal fissure separates the superior and middle lobes. It passes with the visceral pleura, and is a separate respiratory unit. The
from the oblique fissure, near the mid-axillary line, horizontally for- vascular and lymphatic arrangements of the segments are described on
wards to the anterior border of the lung, level with the sternal end of page 959.


the fourth costal cartilage, then passes posteriorly to the hilum on the
mediastinal surface. The horizontal fissure is usually visible on a frontal
chest radiograph. The oblique fissure is usually visible on a lateral PULMONARY HILA
radiograph and on a high-resolution CT scan as a curvilinear band from
the lateral aspect to the hilum (Fig. 54.4). The smaller middle lobe is The pulmonary root connects the medial surface of the lung to the heart
wedged between the superior and inferior lobes, and includes some and trachea, and is formed by a group of structures that enter or leave


Pleura, lungs, trachea and bronchi
958
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noitces
A B
C D
Fig. 54.4 A, An axial section through the lungs below the carina, demonstrating the left and right oblique fissures. The circular avascular area anterior to
the right oblique fissure and surrounded by a halo of white (arrow) is due to the horizontal fissure. In this individual, the fissure is slightly domed and
passes through the plane of the section. B, An axial section through the lungs at the mid left atrial level, demonstrating the left and right oblique fissures
(arrows) as they pass more anteriorly and separate the lower lobes from the lingula and middle lobes. C, A sagittal section through the right lung,
demonstrating the oblique (down-pointing arrow) and horizontal fissures (horizontal arrow). D, A sagittal section through the left lung, demonstrating the
oblique fissure (arrow).
Table 54.1 Bronchopulmonary segments Right hilum
Right lung Left lung
The right root is situated behind the superior vena cava and right
Superior lobe I, apical; II, posterior; III, anterior I, apical; II, posterior; III, anterior;
atrium, inferior to the terminal part of the azygos vein. The usual
IV, superior lingular; V, inferior lingular
sequence of hilar structures, from superior to inferior, is superior lobar
Middle lobe IV, lateral; V, medial –
(eparterial) bronchus, pulmonary artery, principal bronchus and infe-
Inferior lobe VI, superior (apical); VII, medial VI, superior (apical); VII, medial basal;
rior pulmonary vein (see Fig. 54.2B).
basal; VIII, anterior basal; IX, VIII, anterior basal; IX, lateral basal;
lateral basal; X, posterior basal X, posterior basal
Left hilum
The left root lies inferior to the aortic arch and anterior to the descend-
ing thoracic aorta. The usual vertical sequence of structures at the left
the hilum (see Figs 54.2B–54.3B, 54.6C,D). These are the principal hilum is pulmonary artery, principal (hyparterial) bronchus and infe-


bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, a rior pulmonary vein (see Fig. 54.3B). The pulmonary artery is longer
pulmonary autonomic plexus, lymph vessels, bronchopulmonary on the left side, and each of its branches from the hilum to the oblique
lymph nodes and loose connective tissue, all enveloped by a pleural fissure must be identified in pulmonary resections.
sleeve. The pulmonary roots, or pedicles, lie opposite the bodies of the
fifth to seventh thoracic vertebrae. The phrenic nerve, pericardiaco-
phrenic vessels and anterior pulmonary plexus are common anterior SECONDARY PULMONARY LOBULES
relations of both hila. The vagus nerve and posterior pulmonary plexus
are common posterior relations and the pulmonary ligament is a Each segmental bronchus supplies a bronchopulmonary segment. Pro-
common inferior relation. The major structures in both roots are simi- gressive subdivisions of the bronchi occur within each segment, and the
larly arranged: the superior of the two pulmonary veins is anterior, the bronchi become increasingly narrow. All intrapulmonary bronchi are
pulmonary artery and principal bronchus are more posterior, and the kept patent by cartilaginous plates that decline in size and number, and
bronchial vessels are most posterior. The arrangement of bronchopul- finally disappear when bronchi become bronchioles (less than 1 mm
monary segments and the pulmonary hila permit the resection of in diameter). The secondary lobule is the smallest macroscopic subsec-
abscesses and localized primary lung malignancy. tion of the peripheral lung, bounded by connective tissue septa of


lungs
959
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Fig. 54.5 Lungs and bronchi: anterior aspect. The
lobar and segmental bronchi are projected on to
the lung in different colours (compare with Fig.
54.6). (With permission from Waschke J, Paulsen
F (eds), Sobotta Atlas of Human Anatomy, 15th
ed, Elsevier, Urban & Fischer. Copyright 2013.)
uneven size and shape. It consists of approximately six terminal bron- Pulmonary arteries
chioles, the latter being the most peripheral bronchioles not to have
alveoli in their walls. Distal to each terminal bronchiole is an acinus,
The right pulmonary artery divides into two large branches as it emerges
the functional unit of the lung for gas exchange, which consists of 3–4
behind the superior vena cava (Fig. 54.8). This intimate relationship
orders of respiratory bronchioles, each leading to 3–8 orders of alveolar
facilitates the cavopulmonary anastomosis (the Glenn shunt) conceived
ducts. The walls of these ducts consist of alveolar sacs or the mouths
to bypass the defective right heart chambers in various congenital
of alveoli. The primary lobule is the lung distal to the respiratory
cardiac disorders. A lymph node usually lies adjacent to the bifurcation.
bronchiole.
The smaller branch to the superior lobe usually divides again, supplying
the majority of that lobe. The inferior branch descends anterior to the
bronchus intermedius (see below) and posterior to the superior pul-
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
monary vein. It provides a small recurrent branch to the superior lobe,
and then, at the point where the horizontal fissure meets the oblique
The lungs have two functionally distinct circulatory pathways. The pul- fissure, it gives off the branch to the middle lobe anteriorly, and a
monary vessels convey systemic deoxygenated blood to the alveolar branch to the superior segment of the inferior lobe posteriorly. It then
walls and drain oxygenated blood back to the left atrium for systemic continues a short distance before dividing to supply the rest of the
distribution by the left ventricle. The much smaller bronchial vessels, inferior lobe segments.


which are derived from the systemic circulation, provide oxygenated The left pulmonary artery emerges from within the concavity of the
blood to lung tissues that do not have close access to atmospheric aortic arch and descends anterior to the descending aorta to enter
oxygen, i.e. those of the bronchi and larger bronchioles. the oblique fissure (see Fig. 54.8). The ligamentum arteriosum skirts
The pulmonary trunk bifurcates into right and left pulmonary arter- between the superior aspect of the left pulmonary artery and the proxi-
ies that approach the hila of the lungs. Each artery divides into branches mal descending aorta. The left recurrent laryngeal nerve winds around
that accompany the segmental and subsegmental bronchi, mostly in a the aorta, to the left of the ligament; the aorta is relatively fixed by the
posterolateral position. The pulmonary capillaries form single-layered ligament, and so may be ruptured in cases of major trauma associated
and exceedingly thin-walled plexuses immediately outside the epithe- with rapid deceleration. The branches of the left pulmonary artery are
lium in the walls and septa of the alveoli and alveolar sacs. Pulmonary extremely variable. The first and largest branch is usually given off to
veins, two from each lung, drain the pulmonary capillaries; their root- the anterior segment of the left superior lobe. Before reaching the
lets coalesce into larger and more freely communicating veins that oblique fissure, the artery gives off a variable number of other branches
traverse the lung, for the most part independently of the pulmonary to the superior lobe, and, as it enters the fissure, it usually supplies a
arteries and bronchi. At the hilum, the pulmonary vessels accompany large branch to the superior segment of the inferior lobe. Lingular
the main bronchial divisions; the veins are anteromedial and the arter- branches arise within the fissure, and the rest of the lower lobe is sup-
ies posterolateral to the bronchi. This is not the case in the broncho- plied by many varied branching patterns. It was a surgical aphorism of
pulmonary segments, where a segmental bronchus, its branches and the late Lord Brock that when performing a left upper lobectomy, ‘there


associated arteries occupy a central position but the many tributaries of was always one more branch of the pulmonary artery than you thought!’
the pulmonary veins run between segments, serving adjacent segments
(which therefore drain into more than one vein). Some veins also lie Pulmonary sequestration
beneath the visceral pleura, including the pleura in the interlobar fis- When a portion of lung exists without the appropriate bronchovascular
sures. It follows from this that a bronchopulmonary segment is not a connections, it is usually supplied by the systemic vasculature (thoraco-
complete vascular unit with an individual bronchus, artery and vein. abdominal aorta or branches) and drains into either atrium, superior
During resection of segments, it is obvious that the planes between vena cava or azygos veins (Clements 1999) (Figs 54.9–54.10). Extra-
them are not avascular but are crossed by pulmonary veins and some- lobar pulmonary sequestration segments are covered by visceral pleura
times by branches of arteries. This pattern of bronchi, arteries and veins and usually found below the left inferior lobe, whereas intralobar
exhibits considerable variation; veins are the most variable, and arteries abnormalities are usually embedded in normal lung: classically, the
are more variable than bronchi. posterior basal segment of the left inferior lobe. Extralobar pulmonary


Pleura, lungs, trachea and bronchi
959.e1
45
retPahc
Unilateral absence of a pulmonary artery is a rare congenital abnor-
mality characterized by normal lung volume and anatomy at birth.
Revascularization before the age of 6 months avoids the development
of lung hypoplasia (Alison et al 2011). The left pulmonary artery sling
is a congenital abnormality characterized by the left pulmonary artery
arising from the right pulmonary artery, coursing over the right princi-
pal bronchus and heading posteriorly between the trachea and oesopha-
gus. This abnormality is associated with significant tracheobronchial
stenosis (Zhong et al 2010).


Pleura, lungs, trachea and bronchi
960
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A Right lung C
Superior lobe
Apical segment (S I)
I
I
Posterior segment (S II)
II
Anterior segment (S III)
II
Middle lobe
III Lateral segment (S IV) III VI
Medial segment (S V)
VI Inferior lobe
Superior segment (S VI)
IV
Medial basal segment (S VII) VII
V
Anterior basal segment (S VIII) X
VIII V
X IX Lateral basal segment (S IX)
Posterior basal segment (S X)
IX
VIII
B D
I
Left lung I
Superior lobe II
II
Apicoposterior segment (S I + II)
III
Anterior segment (S III) III VI
Superior lingular segment (S IV) VI
Inferior lingular segment (S V)
IV
Inferior lobe IV
Superior segment (S VI) V
Medial basal segment (S VII)* VIII
IX
V X
Anterior basal segment (S VIII) X
Lateral basal segment (S IX) VIII
Posterior basal segment (S X) IX
Fig. 54.6 Bronchopulmonary segments of the right and left lungs, coloured to indicate the different territories. A, Right lung, lateral aspect. B, Left lung,
lateral aspect. C, Right lung, medial aspect. D, Left lung, medial aspect. *Usually, this segment is not a separate unit but is fused with the anterior basal
segment. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
sequestration per se is asymptomatic but is often associated with other junctions, tributary veins finally form a single lobar trunk, i.e. three in
congenital abnormalities: pulmonary hypoplasia, congenital diaphrag- the right lung, two in the left. The right middle and superior lobar veins
matic hernia, congenital cystic adenomatoid malformation and con- usually unite and so two veins, superior and inferior, leave each lung.
genital heart disorders (Stocker et al 1978, Kravitz 1994). A fistula with At the pulmonary hilum, the usual distribution of veins is as follows.


the oesophagus may also develop (Ch. 52). Consideration of differen- The superior pulmonary vein is anteroinferior to the pulmonary artery,
tial diagnosis with mediastinal or pulmonary tumours is mandatory. and the inferior pulmonary vein is the most inferior hilar structure and
also slightly posterior. On the right, the union of apical, anterior and
Pulmonary embolism and arteriography posterior veins (draining the upper lobe) with a middle lobar vein
formed by lateral and medial tributaries constitutes the right superior
Available with the Gray’s Anatomy e-book pulmonary vein. The right inferior pulmonary vein is formed by the
hilar union of superior (apical) and common basal veins from the lower
lobe. The union of superior and inferior basal tributaries forms the
Pulmonary veins
common basal vein. Occasionally, the three right lobar veins remain
separate. The right superior pulmonary vein passes posterior to the
There are usually four pulmonary veins, two from each lung. They origi- superior vena cava, the inferior behind the right atrium.
nate from capillary networks in the alveolar walls and return oxygenated The superior left pulmonary vein is formed by the union of apico-
blood to the left atrium. All the main tributaries of the pulmonary veins posterior, anterior and lingular veins. The left inferior pulmonary vein
receive smaller tributaries, both intra- and intersegmental; by serial is formed from the union of the superior (apical) and common basal


Pleura, lungs, trachea and bronchi
960.e1
45
retPahc
A thrombus that has developed in the deep veins (usually leg or pelvic) blood. Ventilation/perfusion scans with radiolabelled xenon and tech-
may embolize and travel in the right side of the circulation through netium usually demonstrate segmental abnormalities in perfusion
the right atrium and ventricle, lodging in the pulmonary vasculature. with normal ventilation in the corresponding regions. Pulmonary
The clinical abnormalities observed depend on the size of the embolus emboli may also be evaluated by contrast-enhanced spiral CT or pul-
and on the number and frequency of embolic episodes. Large emboli monary angiograms and appear as filling defects. Repetitive emboliza-
may lodge in the main pulmonary artery branches and cause right tion may eventually lead to a dramatic reduction of the pulmonary
ventricular dysfunction and hypoxia, representing a medical emer- vascular bed and chronic cor pulmonale. Thrombolysis, anticoagula-
gency. Smaller emboli may lodge in segmental pulmonary arteries and tion or inferior vena caval filters prevent progression or recurrence of
cause pleuritic chest pain, shortness of breath and haemoptysis but the embolism. A clot may also traverse a patent foramen ovale and lodge
clinical picture is rarely pathognomonic. Pulmonary emboli cause a in the arterial system (paradoxical embolism), most severely in the
ventilation/perfusion mismatch that can have serious physiological cerebral circulation, causing a stroke (Kent and Thaler 2011).
implications leading to a significant reduction in the oxygenation of
Contrast enhancement within left
lower lobe intralobar sequestration
Descending aorta Systemic arterial feeding vessel
Intralobar sequestration Fig. 54.10 The systemic arterial blood supply from the abdominal aorta to
an intralobar sequestration in the left lower lobe of the lung in a
Fig. 54.9 A lung window axial view showing an intralobar sequestration in
15-month-old girl. (Courtesy of Mr Hany Gabra & Mr Jonathan Goring,
the left lower lobe of the lung in a 15-month-old girl. (Courtesy of Mr
Great North Children’s Hospital, Newcastle upon Tyne, UK.)
Hany Gabra & Mr Jonathan Goring, Great North Children’s Hospital,
Newcastle upon Tyne, UK.)


lungs
961
45
retPahc
Thyroid cartilage
Median cricothyroid ligament
Cricoid cartilage
Right principal bronchus Left principal bronchus
Apical bronchus of superior lobe (B1) Apical bronchus of superior lobe (B1)
Posterior bronchus of superior lobe (B2) Posterior bronchus of superior lobe (B2)
Left apicoposterior segment of
Superior lobar bronchus superior lobe (B1 and B2)
Anterior bronchus of superior lobe (B3)
Anterior bronchus of superior lobe (B3)
Bronchus intermedius
Lingular bronchus
Middle lobar bronchus
Superior lingular bronchus (B4)
Lateral segment of middle lobe (B4)
Inferior lingular bronchus (B5)
Medial segment of middle lobe (B5)
Anterior basal bronchus (B8) Superior (apical) Anterior basal bronchus (B8)
bronchus of
Lateral basal bronchus (B9) inferior lobe (B6)
Medial basal bronchus (B7)
Lateral basal bronchus (B9)
Posterior basal bronchus (B10)
Fig. 54.7 The cartilages of the larynx, trachea and bronchi, anterior aspect. The bronchopulmonary segments are shown in brackets. (Redrawn from an
original figure drawn from a metal cast made by the late Lord Russell Brock, GKT School of Medicine, London.)
veins, the latter formed by the union of a superior and an inferior deep lymphatic vessels; these connections direct lymph from the deep
basal vein. Both left superior and inferior pulmonary veins pass ante- to the superficial channels when outflow from deep vessels is obstructed
rior to the descending thoracic aorta. Sometimes, the two left pulmo- by pulmonary disease. There is a tendency for vessels from the superior
nary veins form a single trunk, or they may be augmented by an lobes to pass to the superior tracheobronchial nodes, and those from
accessory lobar vein from each lobe, which unite to form a third left the inferior lobes to pass to the inferior tracheobronchial group.
pulmonary vein. However, lymphatic vessels of adjoining lobes connect deep in the fis-


The right and left pulmonary veins perforate the fibrous pericardium sures and so these connections are not exclusive. At the level of pulmo-
and open separately in the posterosuperior aspect of the left atrium (see nary lobation, the arrangement of lymphatic vessels follows the central
Figs 57.3, 57.4B). Their terminations are separated medially by the artery of a lobule and its peripheral veins. Lymphoid aggregations, non-
oblique pericardial sinus, and laterally by smaller and variable pulmo- follicular in appearance, occur in peribronchial sites and in ‘placoid’
nary venous pericardial recesses that are directed superomedially. The formations deep to the pulmonary pleura.
pulmonary veins are devoid of valves.
The variable incorporation of the primitive pulmonary vein into the
left atrium means that the number of main pulmonary veins may differ. INNERVATION
The left atrium is the heart chamber most posterior and median in
position, and so the length of the left and right pulmonary veins is The autonomic nervous system controls many aspects of airway func-
equal, unlike the arteries and bronchi, where there are conspicuous tion, including regulation of airway smooth muscle tone, mucus secre-
left–right differences in length. The terminal parts of the pulmonary tion from submucosal glands and surface epithelial goblet cells, vascular
veins are surrounded by atrial myocardium; these areas represent poten- permeability and blood flow (Belvisi 2002).
tial accessory re-entrant circuits responsible for the initiation or main-
tenance of supraventricular tachycardias or atrial fibrillation and may Pulmonary plexuses
be percutaneously ablated. Pulmonary vein atresia is a rare congenital
abnormality (Kozak et al 2011).
The pulmonary plexuses lie anterior and posterior to the other hilar
structures of the lungs (see Figs 56.7, 57.61). The anterior plexus is
Lymphatic drainage
small and is formed by rami from vagal and sympathetic cervical
cardiac nerves via connections with the superficial cardiac plexus. The
The pulmonary lymphatics originate in superficial and deep plexuses. posterior pulmonary plexus is formed by the rami of vagal and sympa-


The superficial plexus lies deep to the visceral pleura; its efferents turn thetic cardiac branches from the second to fifth or sixth thoracic sym-
around the margins of the lung and its fissures, eventually reaching pathetic ganglia. The left plexus also receives branches from the left
the bronchopulmonary nodes. The alveoli have no lymph vessels. The recurrent laryngeal nerve. Further details of the pulmonary plexuses are
deep lymphatics originate at bronchiolar level and follow the broncho- given in the description of the cardiac plexuses on page 1021. The sym-
vascular divisions to the hilum, ending in the same nodes. No free pathetic nervous system (noradrenaline (norepinephrine)) acting on
anastomoses exist between the two systems, except at the hilum and β-receptors produces bronchodilation; the parasympathetic nervous
peripherally, where small but dilatable channels connect superficial and system (acetylcholine) acting on muscarinic M3 receptors maintains


Pleura, lungs, trachea and bronchi
962
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Fig. 54.8 The relationship between
the central airways and the
Trachea
pulmonary vessels. The numbers in
Right principal bronchus Arch of aorta the lower figure denote the numbers
of the bronchopulmonary segments.
Left principal bronchus
Right pulmonary artery
Left pulmonary artery
Right superior lobar bronchus
Pulmonary trunk
Ascending aorta
Left superior pulmonary vein
Right superior pulmonary vein
Right inferior pulmonary vein Left inferior pulmonary vein
1
2
1
1 & 2
2
3
3
4
4
5
6
5
6
7 8
8
9
10
10
9
the resting tone of the bronchiolar smooth muscle. Prostaglandins 60–80 m2 surface. The capillary blood transit time at rest is 0.75 s,
have various effects: PGI produces bronchodilation (acting on IP halving with exercise.
2
receptors) or bronchoconstriction (acting on EP receptors); PGF
1 2α
produces bronchoconstriction. Alveolar structure
The alveoli are thin-walled pouches that provide the respiratory surface
MICROSTRUCTURE OF RESPIRATORY SURFACES
for gaseous exchange (Figs 54.11–54.13). Their walls contain two types
of epithelial cell (pneumocytes) and cover a delicate connective tissue
Thin-walled respiratory surfaces (alveoli) are distributed as isolated
within which a network of capillaries ramifies. Since the walls are
patches within the walls of respiratory bronchioles and as tube-like
extremely thin, they present a minimal barrier to gaseous exchange
alveolar ducts and balloon-like alveolar sacs that contain groups of
between the atmosphere and the blood in the capillaries. Adjacent
adjacent alveoli.
alveoli are frequently in close contact; the intervening connective tissue
forms the central part of the interalveolar septum. Alveolar macro-
Alveolar area
phages are present within the alveolar lumen and migrate over the
epithelial surface.
Both human lungs contain 300–500 million alveoli, giving a total
surface area of 70–100 m2. These values vary considerably between Interalveolar septum


normal young individuals; the differences become even more marked The alveolar lining epithelium varies in thickness, but extensive areas
with age and as a consequence of degenerative changes. The number of of it are as little as 0.05 µm thick (see Fig. 54.13). The epithelium lies
alveoli increases from approximately 10 million at birth to the adult on a basal lamina that is fused with the basal lamina that surrounds
value, mainly in the first 8 years; thereafter, the increase in lung volume the adjacent capillaries in the thin portions of a septum. The total
is achieved through augmentation of alveolar volume (Narayanan et al barrier to diffusion between air and blood in these thin portions may
2013). Their inflated diameter varies with lung position, and is greater be as little as 0.2 µm. The thick portions of a septum contain connective
in the superior regions than in the inferior because of the increased tissue elements, including elastic and collagen type III fibres, resident
gravitational pressure at the lung base. Although the lung enlarges in and migratory cells (see Fig. 54.12).
all directions during inspiration, most of the change in volume appears
to be due to the lengthening and expansion of the alveolar ducts and Alveolar epithelial cells (pneumocytes)
increase in the size of the openings into the air sacs; the inspiratory The alveolar epithelium is a mosaic of type I and II pneumocytes. Type
change in the volume of the gas-conducting system is insignificant. The I pneumocytes are simple squamous epithelial cells and form over 90%
combined alveolar and capillary surface area for gas exchange is of the alveolar area. Their basal laminae fuse with that of the adjacent


lungs
963
45
retPahc
Trachea
Left principal
(primary) bronchus
Lobar
(secondary) bronchus
Segmental
(tertiary) bronchus
leading
after several
successive
divisions to
Terminal bronchus
Fig. 54.11 The respiratory tree and its arterial blood supply, venous and lymphatic drainage, and nerve supply. The distribution of the different epithelial
cells is shown. Blue is used for vessels that contain deoxygenated blood, and red for vessels that contain oxygenated blood.
noitrop
gnitcudnoC
noitrop
yrotaripseR
Regional distribution of the cell types in the respiratory tract epithelium
(in approximate order of frequency in the region)
Ciliated columnar epithelial cells
Goblet cells
Basal cells
Seromucous gland cells
Neuroendocrine cells
Brush cells
Ciliated cuboidal epithelial cells
Basal cells
Seromucous gland cells (upper part of region only)
Brush cells
Ciliated and non-ciliated cuboidal epithelial cells
Clara cells
Brush cells
Ciliated and non-ciliated cuboidal epithelial cells
Clara cells
Type I pneumocytes
Type I pneumocytes
Type II pneumocytes
Lumen of small bronchus
Pulmonary artery
Elastic network deep to
smooth muscle fibres
Smooth muscle fibres
Seromucous gland
Cartilage plate
Bronchial artery
Lobular bronchiole
Terminal bronchiole
Terminal bronchiole
Respiratory bronchiole
Respiratory bronchiole
Alveolar duct
Atrium
Alveolus
Alveolar sac
Endothoracic fascia
Parietal pleura
Pulmonary Interalveolar Submesothelial Pleural cavity
vein septum connective tissue Elastin network Visceral pleural mesothelium
Capillary network Conduit between in alveolar wall
in alveolar wall alveolar duct and
alveolar sac Alveolus
capillary endothelium to form the thin portions of interalveolar Together with a similar endothelial barrier, this arrangement limits the
septa. Their thin cytoplasm (0.05–0.2 µm) facilitates gaseous diffusion movement of fluid from blood and interstitial spaces into the alveolar


between the lumen of the alveolus and its capillaries. The edges of lumen (the blood–air barrier). If damaged, type I cells, which do not
adjacent cells overlap; they are joined by tight junctions, creating a strict divide, are replaced by type II cells, which proliferate and differentiate
diffusion barrier between the alveolar surface and underlying tissues. into type I pneumocytes.


Pleura, lungs, trachea and bronchi
964
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Bronchiolar epithelial cell types:
Brush
Neuroendocrine
Ciliated
Non-ciliated
Clara
Interalveolar septum
Alveolar macrophage
Alveolar epithelial cell
(pneumocyte) types:
Type I
Type II
Interalveolar pore
(of Kohn)
Fig. 54.12 The respiratory portion of the lung and its cell types.
The smaller type II cells are often more numerous than type I cells, clear the respiratory spaces of inhaled particles that are small enough
but they contribute less than 10% of the alveolar surface area. They are to reach the alveoli (hence their alternative name of ‘dust cells’; see Fig.
rounded and protrude from the alveolar surface, particularly at the 4.13). Most of them migrate with their phagocytosed load to the bron-
angles between alveolar profiles. In the human lung, they are often chioles, where they are swept into the mucociliary rejection current and
associated with interalveolar pores of Kohn. Their cytoplasm contains removed from the lung. Others migrate through the epithelium of the
numerous characteristic secretory lamellar bodies consisting of concen- alveoli into the lymphatics that drain the connective tissue of the lung,
tric whorls of phospholipid-rich membrane, the precursors of alveolar and so pass into lymphoid tissue around the pulmonary lobules. Under
surfactant, which they can recycle (see Fig. 54.13C). normal conditions, alveolar macrophages have a granular cytoplasm
because they contain phagocytosed particles; in smokers, the particles
Interalveolar pores of Kohn have a characteristic appearance and are called ‘tar bodies’. When
Interalveolar pores of Kohn are small pores lined by epithelium (usually actively phagocytic, macrophages release proteases: if antiproteases (e.g.
type II alveolar cells), which cross interalveolar septa to link adjacent α-antitrypsin) that are normally present in the alveolar lining are defi-
1
alveolar airspaces. Humans have up to seven pores per alveolus, ranging cient, macrophage activity may damage the lung. Alveolar macrophages


in size from 2 to 13 µm. These small passages may sustain the flow of are involved in the turnover of surfactant.
air in the event of blockage of one of the alveolar ducts and also provide Alveolar macrophages can be recovered from sputum and are of
routes of migration for alveolar macrophages, bacteria and viruses. diagnostic importance if they appear abnormal. For instance, whenever
erythrocytes leak from pulmonary capillaries, the macrophages that
Alveolar macrophages
engulf the extravasated cells become brick-red and are detectable in
Alveolar macrophages are derived from circulating monocyte precursors ‘rusty’ sputum. They are typical of congestive heart failure and often
(see Fig. 4.12). They originate in haemopoietic tissue in the bone termed ‘heart-failure cells’. Macrophages that migrate back into the
marrow, migrate into the alveolar lumen from adjacent blood vessels connective tissue of the lung settle in patches that are visible beneath
and connective tissue, and wander about on the epithelial surfaces. They the visceral pleura, e.g. carbon-filled cells give the lungs a mottled


trachea and bronchi
965
45
retPahc
A
P
1
C1
BL
E
Er
C
2
A
P E B
1
C
2
C
2
A
P
2
L
A C
Fig. 54.13 A, An electron micrograph showing the septum between three adjacent alveoli (A). The septum contains two capillaries (C and C) in section;
1 2
the lower one is cut obliquely through the nucleus of an endothelial cell (E). Type I pneumocytes (P) line the alveolar airspaces except where a type II
1
pneumocyte (P), with cytoplasmic lamellar bodies (L), intervenes. B, The thin portion of an interalveolar septum. Part of an erythrocyte (Er) is shown in
2
the capillary lumen, lined by endothelium (E). The alveolar airspace (right) is lined by a type I pneumocyte (P). The two cells share a basal lamina (BL).
1
C, Cytoplasmic lamellar bodies in a type II pneumocyte are composed mainly of phospholipids that contribute to the surfactant secreted by these
pneumocytes and by Clara cells of the respiratory bronchioles. (With permission from Young B, Heath JW 2000 Wheater’s Functional Histology.
Edinburgh: Churchill Livingstone.)
appearance. However, if the inhaled particles are abrasive or chemically
TRACHEA AND BRONCHI
active, they may elude macrophage removal and damage the respiratory
surface, producing fibrosis and a concomitant reduction in the respira-
tory area. This occurs in many industrial diseases, e.g. pneumoconiosis TRACHEA
caused by coal dust, or asbestosis, where the long thin fibres of asbestos
can cause considerable damage and may trigger fatal mesothelioma in The trachea is a 10–11 cm long tube formed of cartilage and fibromus-
the pleural lining. cular membrane, and lined internally by mucosa. It descends from the
larynx at the level of the sixth cervical vertebra and divides into right
and left principal bronchi typically inferior to the sternal plane, level
Alveolar surfactant


with the upper half of the sixth thoracic vertebra (see Fig. 51.6). It lies
approximately in the sagittal plane but its point of bifurcation is usually
The alveolar surface is normally covered by a film of pulmonary sur- a little to the right. The trachea is mobile and can rapidly alter in length,
factant, which is a complex mixture mainly of phospholipids (particu- such that the bifurcation reaches the level of the sixth thoracic vertebra
larly dipalmitoylphosphatidylcholine and phosphatidylglycerol), with during deep inspiration. In children with full neck extension, the length
some protein and neutral lipid. Surfactant is stored in lamellar bodies of the trachea increases by 0.95 ± 0.43 cm; this elongation is insufficient
and secreted in the form of tubular myelin (unrelated to myelin of the to prevent displacement of the tip of an endotracheal tube towards the
nervous system) by type II pneumocytes. It is recycled by type II pneu- vocal cords in intubated children (Jin-Hee et al 2005).
mocytes, or cleared (i.e. phagocytosed) by alveolar macrophages. Clara The anterolateral portion of the trachea consists of 16–20 superim-
cells of the bronchiolar epithelium are believed to secrete surfactant of posed incomplete rings of hyaline cartilage and intervening fibroelastic
a different composition. tissue (the latter allows tracheal inspiratory elongation). The posterior
Surface tension at the alveolar surface is very high because the alveoli aspect is a flat, fibromuscular wall. The trachea is funnel-shaped in
are minute and spherical; these features oppose expansion during inspi- neonates, when the upper end is wider than the lower end, and gradu-
ration, and tend to collapse the alveoli in expiration. The detergent-like ally becomes cylindrical with increasing age. The external transverse
properties of pulmonary surfactant greatly reduce the surface tension diameter is typically 2 cm in adult males and 1.5 cm in adult females.
and make ventilation of the alveoli much more efficient. As the volume In the first postnatal year, the tracheal diameter does not exceed 4 mm.


of an alveolus alternatively increases and decreases, so does its surface Mean transverse diameter is greater than anteroposterior diameter up
area. With a fixed amount of surfactant in the alveolar film, the relative to the age of 6 years and, after that, the two diameters are nearly equal
concentration of surfactant increases on exhalation. The fortunate result (Griscom and Wohl 1986); during later childhood, tracheal diameter
is a decrease in collapsing tendency as the alveolar volume decreases, in millimetres is approximately equal to age in years. The lumen is
stabilizing the alveolus and overcoming the tendency of small gas about 12 mm in diameter in live adults but increases as a result of
spaces to obliterate. relaxation of the smooth muscle post mortem. The transverse shape of


Pleura, lungs, trachea and bronchi
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the lumen is variable, especially in the later decades of life, and it may branches, such as: double aortic arch, right aortic arch, aberrant right
be round, lunate or flattened. At bronchoscopy, the posterior wall of subclavian artery, double ductus arteriosus or persistence of the fifth
the trachea bulges into the lumen and this is exaggerated in expiration aortic arch.
and coughing. The distal end of the trachea is visible as a concave spur.
A tracheal bronchus may occasionally arise, mainly from the right
aspect of the trachea, as either a supernumerary or a displaced superior RIGHT PRINCIPAL BRONCHUS
lobe bronchus (porcine bronchus). A tracheal bronchus was noted in
2.4% of children undergoing bronchoscopy for respiratory symptoms The right principal bronchus is approximately 2.5 cm long, and is
(Wong et al 1999). The variable position of the trachea in children wider, shorter and more vertical than the left (see Fig. 54.7; Fig. 54.14A).
makes it unreliable as an indicator of the presence of a right-sided aortic These differences explain why inhaled foreign bodies enter the right
arch on a chest radiograph. In children with a right-sided aortic arch, principal bronchus more often than the left (more common in children
the trachea is on the right in 47% of cases, in the midline in 33% and who may present with breathlessness, unilateral wheeze or recurrent
on the left in 7% (Strife et al 1989). Tracheal agenesis is a rare and aspirations; a chest radiograph may show air trapping in the affected
usually lethal congenital abnormality. lobe). The right principal bronchus gives rise to its first branch, the
superior lobar bronchus, then enters the right lung opposite the fifth
Relations of the cervical part of thoracic vertebra. The azygos vein arches over it, and the right pulmo-
the trachea nary artery lies at first inferior, then anterior to it (the eparterial bron-
chus). After giving off the superior lobar bronchus, which arises