reference to the terminal oesophagus, stomach, duodenum, spleen, the lesser sac of the peritoneum and the omenta, seen in semicoronal section (left
column) and transverse section at the levels indicated by the arrows (right column). D–E, The lesser sac and dorsal and ventral mesogastria.
mesogastrium. The right pneumatoenteric recess undergoes further mesooesophagus; the much larger ventral mesogastrium, and the
extension, subdivision and modification (see Fig. 60.7 A(i), B(i)). most caudal free border, is from the ventral mesoduodenum. As dif
From its caudal end, a second process of cleft and cavity formation ferential growth of the duodenum occurs, the biliary duct is reposi
occurs, which produces the hepatoenteric recess. This thins and tioned and most of the duodenum becomes sessile. The duodenal
expands the splanchnopleure between the liver and the stomach and attachment of the free border and a continuous neighbouring strip of
proximal duodenum, and reaches the diaphragm (see Fig. 60.7A(i), the lesser omentum become confined to the upper border of a short
C(i)). The resulting, structurally bilaminar, mesenteric sheet is the segment of its superior part. The contrasting growth and positioning of
lesser omentum. It is derived, cranially to caudally, from the small its attached viscera cause the free border to change gradually from the


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RETPAHC
horizontal to the vertical. It carries the bile duct, portal vein and meet and blend. It provides a mesenchymal route for the upper abdom
hepatic artery, and its hepatic end is reflected around the porta hepatis. inal, transdiaphragmatic and transpericardial parts of the inferior vena
An alternative name for this part of the lesser omentum is the hepa cava, and it is also prominent in the development of parts of the liver,
toduodenal ligament; it forms the anterior wall of the epiploic lesser sac of peritoneum, and certain mesenteries. The left fold regresses
foramen. The floor of the foramen is the initial segment of the superior whereas the right fold enlarges rapidly (see Fig. 60.7A).
part of the duodenum, its posterior wall is the peritoneum covering The pneumatoenteric recess continues to expand to the right into
the immediately subhepatic part of the inferior vena cava, and its roof the substance of the caval fold. It stops near the left margin of the
the peritonealized caudate process of the liver. The major part of the hepatic part of the inferior vena cava, which remains extraperitoneal
lesser omentum from the lesser gastric curvature passes in an approxi and crosses the base of the now roughly triangular bare area of the liver
mately coronal plane to reach the floor of the increasingly deep groove and this new expanded line of reflection. With closure of the pleuro
for the ductus venosus on the hepatic dorsum; this part is sometimes peritoneal canals, the rostral part of the right pneumatoenteric recess is
called the hepatogastric ligament. sequestered by the diaphragm but often persists as a small serous sac
in the right pulmonary ligament. The remaining caval fold mesen
Ligaments of the liver
chyme to the left of the inferior vena cava – which forms the right wall
The liver is precociously large during development because of its early of the upper part of the lesser sac – becomes completely invaded by
role in haemopoiesis. Thus, the liver mass projects into the abdominal embryonic hepatic tissue and is transformed into the caudate lobe of


cavity with equal growth on the two sides of the peritoneal cavity. The the liver. This smooth, vertically elongated, mass projects into the
ligaments associated with the liver develop from the ventral mesogas cavity of the lesser sac; both its posterior, and much of its anterior,
trium – which passes from the foregut to the ventral abdominal wall, surfaces become peritonealized as a result of the increasing depth of
down to the cranial rim of the intestinal portal – and from the reflec the groove for the ductus venosus and the attachment of the lesser
tions of peritoneum from the liver to the diaphragm. omentum to its floor.
The medial portions of the germinative coelomic epithelial walls,
containing splanchnopleuric mesenchyme, septum transversum mesen
Later stages of lesser sac development
chyme and developing liver, constitute the early ventral mesogastrium
(see Fig. 60.5). The mesenchyme between these layers is continuous
superiorly with the septum transversum mesenchyme of the diaphragm. The lower (inferior) part of the lesser sac can be first seen in embryos
The coelomic epithelial layers of the ventral mesogastrium almost touch of 8–9 mm crown–rump length, and the early pneumatoenteric and
anterior and posterior to the liver, and are separated by a slender lamina hepatoenteric recesses are well established. Progressive differential
of mesenchyme. They form the falciform ligament and the lesser gastric growth produces an elliptical transverse sectional profile, with a
omentum, respectively, and where they are in contact with the liver rightsided lesser curvature, which corresponds to the original ventral
directly, they form visceral peritoneum (see Fig. 60.7D). border of the gastric tube. The lesser omental gastric part of the ventral
When the diaphragm is formed above the liver, local cavities coalesce mesogastrium remains attached to this border. The greater curvature of
and open into the general coelomic cavity as extensions of the greater the stomach is a new, rapidly expanding, region; its convex profile
(and lesser) sacs. In this way, almost all the ventrosuperior, visceral and projects mainly to the left, but also cranially and caudally (see Fig.


some of the posterior aspects of the liver become peritonealized. The 60.7A(i), B(i), C(i)). The original dorsal border of the gastric tube now
process of extending the greater sac continues over the right lobe and traverses the dorsal aspect of the expanding rudiment, curving along a
stops when the future superior and inferior layers of the coronary liga line near the lesser curvature. The primitive dorsal mesogastrium is
ment and the right triangular ligament are defined. Those, plus a medial transiently attached to it, and blends with the thick layer of compound
boundary provided by an extension of the lesser sac, enclose the ‘bare gastric mesenchyme clothing the posterior aspect and greater curvature
area’ of the liver, where loose areolar tissue of septum transversum of the miniature stomach. Because of its thickness, the mesenchyme
origin persists. Later in development, when the haemopoietic function projects cranially, caudally and, particularly, to the left, beyond the
of the liver declines, the left lobe becomes relatively smaller than the ‘new’ greater curvature of the endodermal lining of the stomach.
right; this, presumably, accounts for the smaller size of the left triangu The processes already described in relation to the ventral mesenteries
lar ligament. now supervene. Multiple clefts appear at various loci in the mesen
Where the superior layers of the coronary and left triangular liga chyme, and there are local mesenchyme to epithelial transitions. The
ments meet, they continue as a (bilaminar) ventral mesentery attached groups of clefts rapidly coalesce to form transiently isolated closed
to the ventrosuperior aspects of the liver. Its somewhat arched umbilico spaces, which soon join with each other and with the preformed upper
hepatic free caudal border carries the left umbilical vein. As the ventral part of the lesser sac; the newly formed epithelia join the coelomic
body wall develops, this falciform ligament, which initially attaches to epithelium. In sequence, the initial loci occur in the compound poste
the early cranial intestinal portal, is drawn to the diminishing cranial rior gastric mesenchyme nearer the lesser curvature and along its zone


rim of the umbilicus. It may be considered the final ventral part of the of blending with the primitive dorsal mesogastrium; in the dorsal meso
ventral mesogastrium, although its free border has a ventral mesoduo duodenum; and independently, in the caudal rim, where greater curva
denal origin. Its passage to the ventral body wall becomes increasingly ture mesenchyme and dorsal mesogastrium blend. As these cavities
oblique, curved and falciform (sickleshaped) as the umbilicus becomes become confluent and their ‘reniform’ expansion follows, matches and
more defined. then exceeds that of the gastric greater curvature, there are several major
In the early embryo, the connection between one pericardioperito sequelae. The primitive dorsal mesogastrium increases in area by intrin
neal canal and the other was directly across the ventral surface of the sic growth, and, as cavitation proceeds, by incorporating substantial
cranial midgut, immediately caudal to the developing primitive ventral contributions from the dorsal lamella separated by cleavage of the
mesogastrium. By stage 14, the passage from one side of the falciform posterior gastric mesenchyme; it is now called the secondary dorsal
ligament to the other necessitates passing below the greatly enlarged mesogastrium (see Fig. 60.7A(ii)). The gastric attachment of the second
liver, or the curved lower edge of the falciform ligament, or the lesser ary dorsal mesogastrium changes progressively. It may be regarded as a
omentum. The position of the falciform ligament is of clinical interest set of somewhat spiral lines, longitudinally disposed, that move with
in the neonate in diagnosing pneumoperitoneum because it is silhouet time to the left, from near the lesser curvature, towards and finally
ted by air on abdominal Xrays. reaching the definitive greater curvature. The parietal mesogastrial and
(cleaving) mesoduodenal attachment remains in the dorsal midline for
Caval fold a time, but it later undergoes profound changes. With the confluence
The caval fold is a linear eminence, with divergent cranial and caudal of the cavities that collectively form the lower part of the lesser sac, its


ends, which passes from the upper abdominal to the lower thoracic communication with the upper part (which corresponds to the lesser
region and protrudes from the dorsal wall of the pleuroperitoneal canal. gastric curvature and right and left gastropancreatic folds) becomes
Cranially, it becomes continuous, lateromedially, with the root of the better defined. Ventral to the lower part of the cavity, postcleavage
pulmonary anlage and pleural coelom, the uppermost portion of the splanchnopleure covers the posteroinferior surface of the stomach and
septum transversum mesenchyme, and the retrocardiac mediastinal a short proximal segment of the duodenum. This ventral wall is con
mesenchyme. Caudally, it forms an arch with dorsal and ventral horns. tinued beyond the greater curvature and duodenum as the splanchno
The dorsal horn merges with the primitive dorsal mesentery and the pleuric strip of visceral attachment of the secondary dorsal mesogastrium
mesonephric ridge and associated gonad and suprarenal (adrenal) and mesoduodenum. The radial width of the strip is relatively short
gland. The ventral horn is confluent with the dorsal surface of the septal cranially (gastric fundus) and gradually increases along the descending
mesenchyme. left part of the greater curvature. It is longest throughout the remaining
Thus, the caval fold is a zone where intestinal, mesenteric, intermedi perimeter of the greater curvature as far as the duodenum; this promi
ate, hepatic, pericardial, pulmonary and mediastinal mesenchymes nent part shows continued marginal (caudoventral and lateral) growth


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with extended internal cavitation (its walls constitute the expanding vein, portal vein, left renal vessels, the caudal pole of the left suprar
greater omentum; see Fig. 60.6H). The margins of the cavity of the enal gland, a broad ventral band on the left kidney and various
inferior part of the lesser sac are limited by the reflexed edges of the muscles). The intervening peritoneal mesothelia fuse and atrophy, and
ventrally placed strata derived from the secondary dorsal mesogastrium the mesenchymal cores form fascial sheaths and septa. The pancreas is
just described. These converge to form the splanchnopleuric dorsal wall, now sessile. The peritoneum covering the upper left part of its head,
which is initially ‘free’ throughout, except at its midline dorsal root. At neck and the anterosuperior part of its body forms the central part of
roughly midgastric levels, the pancreatic rudiment grows obliquely the dorsal wall of the lesser sac. The pancreatic tail remains perito
encased in this dorsal wall; its tail ultimately reaches the left limit of nealized by a persisting part of the secondary dorsal mesogastrium as
the lesser sac at the level of the junction between gastric fundus and it curves from the ventral aspect of the left kidney towards the hilum
body (see Fig. 60.7C(ii)). of the spleen. The infracolic parts of the pancreas are covered with
greater sac peritoneum. In the greater omental subregion of the lower
Greater omentum part of the lesser sac, two contrasting forms of mesenteric adhesion
The greater omentum continues to grow, both laterally and, particularly, occur. The posterior ‘returning’ bilaminar stratum of the omentum
caudoventrally. It covers and is closely applied to the transverse meso undergoes partial fusion with the peritoneum of the transverse colon
colon, transverse colon and inframesocolic and infracolic coils of small at the taenia omentalis and with its mesocolon. The layers remain


intestine (see Fig. 60.6D–G). At this stage, the quadrilaminar nature of surgically separable; no anastomosis occurs between omental and
the dependent part of the greater omentum is most easily appreciated. colic vessels.
‘Simple’ mesenteries are bilaminar: they possess two mesothelial sur The original dorsal midline attachment to the parietes of the
faces derived from splanchnopleuric coelomic epithelium, which foregut dorsal mesentery is profoundly altered during the develop
enclose a connective tissue core derived from splanchnopleuric mesen ment of the lesser sac and its associated viscera. However, despite the
chyme. In the greater omentum, the gastric serosa covering its postero extensive areas of fusion, virtually the whole of the gastric greater cur
inferior surface (single mesothelium) and the anterosuperior serosa vature (other than a small suboesophageal area) and its topographical
(single mesothelium) converge to meet at the greater curvature and continuation (the inferior border of the first 2–3 cm of the duode
initial segment of the duodenum. The resulting bilaminar mesentery num) retain true mesenteric derivatives of the secondary dorsal mes
continues caudoventrally as the ‘descending’ stratum of the omentum. ogastrium and its continuation, the dorsal mesoduodenum. Although
This, on reaching the omental margins, is reflexed and now passes regional names are used to assist identification and description, it is
cranio dorsally to its parietal root as the ‘ascending’ posterior bilaminar important to emphasize that they are all merely subregions of one
stratum. The two bilaminar strata are, initially, in fairly close contact continuous sheet.
caudally, but are separated by a fine, fluidcontaining, cleftlike exten The upper (oesophagophrenic) part of the lesser omentum arches
sion of the lower part of the lesser sac. The posterior mesothelium of across the diaphragm. As this bilaminar mesentery approaches the
the posterior stratum makes equally close contact with the anterosupe oesophageal hiatus, its laminae diverge, skirting the margins of the


rior surface of the transverse colon, starting at the taenia omentalis, and hiatus. They then descend for a limited distance and with variable
with its transverse mesocolon. inclination, to enclose reciprocally shaped areas on the dorsum of the
gastric fundus and diaphragm. The area may be roughly triangular to
quadrangular; it contains areolar tissue and constitutes the bare area
Maturation of the lesser sac
of the stomach or, when large, the left extraperitoneal space. Its right
lower angle is the base of the left gastropancreatic fold, and its left
At this stage, and subsequently, it is convenient to designate the lower lower angle reconstitutes the bilaminar mesentery. The root of the
part of the lesser sac as consisting of three subregions: retrogastric, peri latter arches downwards and to the left across the diaphragm and
gastric and greater omental (Fig. 60.7C(ii)). The names are self suprarenal gland, and gives the gastrophrenic ligament to the gastric
explanatory but their confines are all modified by various factors. Two fundus. It continues to arch across the ventral surface of the upper
phenomena are particularly prominent: namely, gastric ‘descent’ rela part of the left kidney, and its layers part to receive the pancreatic tail;
tive to the liver, and fusion of peritoneal layers with altered lines of they initially extend to the hilum of the spleen as the splenorenal liga
reflection, adhesion of surfaces and loss of parts of cavities. ment (see Figs 60.6C, 60.7D). The left half of this bilaminar ‘liga
After the third month, hepatic growth, particularly of the left lobe, ment’ provides an almost complete peritoneal tunic for the spleen. It
diminishes and the whole organ recedes into the upper abdomen. then reunites with its fellow at the opposite rim of the splenic hilum,
Meanwhile, the stomach elongates and some descent occurs, despite and continues to the next part of the gastric greater curvature as the
its relatively fixed cranial and caudal ends. This produces the angular gastrosplenic ligament. The remaining part (perhaps twothirds) of


flexure of the stomach, which persists postnatally. The concavity of the the gastric greater curvature and its short duodenal extension provide
lesser curvature is now directed more precisely to the right; the lesser attachment for the anterior, ‘descending’, bilaminar stratum of the
omentum is more exactly coronal and its free border vertical. Ventral greater omentum. Its returning, posterior, bilaminar stratum continues
to the liver, the free border of the falciform ligament passes steeply to its parietal root (which extends from the inferior limit assigned to
craniodorsally from umbilicus to liver (see disposition in the neonate the splenorenal ligament), and curves caudally and to the right along
in Figs 14.6–14.7). The mesenchymal dorsal wall of the lower part of the anterior border of the body of the pancreas, immediately cranial
the lesser sac, which is crossed obliquely by the growing pancreas, has, to the line of attachment of the transverse mesocolon. Crossing the
up to this point, remained free and retained its original dorsal midline neck of the pancreas, the same curve is followed for a few centimetres
root. Substantial areas now fuse with adjacent peritonealized surfaces on to its head; the omental root then sharply recurves cranially and to
of retroperitoneal viscera, the parietes, or another mesenteric sheet or the left, to reach the inferior border of the duodenum. Thus, it reaches
fold. Where sheets fuse, there is a variable loss of apposed mesothelia that part of the lesser sac provided by cleavage of the dorsal mesoduo
and some continuity of their mesenchymal cores, but they remain denum from the greater sac. It enters the epiploic foramen, traverses
surgically separable and no vascular anastomosis develops across the the epiploic canal between the caudate hepatic process and proximal
interzone. Above the pancreas, the posterior secondary dorsomesogas duodenum, then crosses the right gastropancreatic fold, and descends
trial wall of the sac becomes closely applied to the peritoneum behind the proximal duodenum to enter the right marginal strip


covering the posterior abdominal wall and its sessile organs, the dia enclosed by the greater omentum. The definitive origins of the perito
phragm, much of the left suprarenal gland, the ventromedial part of neum from the posterior abdominal wall are shown in the adult in
the upper pole of the left kidney, the initial part of the abdominal Figures 63.1, 68.5, 63.6B.
aorta, the coeliac trunk and its branches, and other vessels, nerves
and lymphatics. Their peritoneal surfaces fuse. However, albeit with Peritoneum associated with the
some tissue loss, a single mesothelium remains covering these struc
mid- and hindgut
tures, intercalated as a new secondary dorsal wall for this part of the
lesser sac.
The pancreas grows from the duodenal loop, penetrating the sub It is convenient to consider the mesenteries of the small and large
stance of the dorsal mesoduodenum and secondary dorsal mesogas intestine after rotation and the principal growth patterns have been
trium; their mesenchymes and mesothelia initially clothe its whole achieved, and the developing pancreas is becoming retroperitoneal.
surface, except where peritoneal lines of reflection exist. Its posterior
Small intestine
peritoneum becomes closely applied to that covering all the posterior
abdominal wall structures it crosses (the inferior vena cava, abdomi Most of the duodenal loop encircles the head of the pancreas and is
nal aorta, splenic vein, superior mesenteric vessels, inferior mesenteric retroperitoneal. The peritoneum principally covers its ventral and


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RETPAHC
convex aspects. Areas not covered are a short initial segment of the eleventh ribs by a phrenicocolic ligament. The latter sometimes
superior (first) part, which is more completely peritonealized because blends with a presplenic fold that radiates from the gastrosplenic liga
it gives attachment to the right margins of the greater and lesser omenta; ment. The descending colon becomes sessile. The process of fusion and
the sites where the transverse colon is closely apposed to the descending obliteration of both ascending and descending mesocolons starts later
(second) part, or where the latter is crossed by the root of the transverse ally and progresses medially.
mesocolon; and the sites where the mesentery crosses the transverse
(third) part, and descends across the ascending (fourth) part from its Sigmoid colon
upper extremity at the duodenojejunal flexure. These regions are illus The sigmoid colon is most variable in its length and disposition. It
trated in the adult in Figure 63.2. In addition, one or more of up to six retains its dorsal mesocolon, but the initial midline dorsal attachment
different duodenal recesses may develop (p. 1108). of its root is considerably modified in its definitive state.
From a mesenteric standpoint, the succeeding small intestine, from
the duodenojejunal flexure to the ileocaecal junction, undergoes less Rectum
modification of its embryonic form than other gut regions. Its early The rectum continues from the ventral aspect of the third sacral vertebra
dorsal mesentery is a continuous, single (but structurally bilaminar) to its anorectal (perineal) flexure anteroinferior to the tip of the coccyx;
sheet, with a midline parietal attachment (line of reflection, or ‘root’). the distance changes with age. All aspects of the rectum are encased by
The attachment of the root becomes an oblique narrow band from the mesenchyme, and the early, dorsally placed, mass is named, by some
left aspect of the second lumbar vertebra to the cranial aspect of the authorities, the dorsal mesorectum. However, the latter does not form


right sacroiliac joint (see Figs 60.6H, 63.2). a true mesentery; with progressive skeletal development, it is reduced
to a woven fibroareolar sheet that displays patterned variations in thick
Ascending colon ness and fibre orientation. The sheet is closely applied to the ventral
The caecum and vermiform appendix arise as a diverticulum from the concavity of the sacrum and coccyx, and encloses numerous fibromus
antimesenteric border of the caudal limb of the midgut loop; conse cular and neurovascular elements. The rectum, therefore, becomes
quently, the caecum does not possess a primitive mesocaecum. These sessile, and visceral peritoneum is restricted to its lateral and ventral
regions of the gut undergo long periods of growth, often asymmetrical, surfaces (see Fig. 72.4).
and their final positions, dimensions and general topography show With the disappearance of the postanal gut by the end of the fifth
considerable variation. The vermiform appendix is almost wholly week, the ventrolateral peritoneum reaches the superior surface of the
clothed with visceral peritoneum, derived from the diverging layers of pelvic floor musculature; this condition persists until late in the fourth
its rather diminutive mesoappendix. The latter should perhaps be month. In the male, the ventral rectal peritoneum is reflected over the
regarded as a direct derivative of the primitive dorsal mesentery, and posterior surface of the prostate, bladder trigone and associated struc
perhaps a similar status for the vascular fold of the caecum should be tures. In the female, the ventral peritoneum initially receives a reflection
considered. that covers almost the whole posterior aspect of the vagina, and is
The colonic gut retains its primitive dorsal mesentery, the mesoco continued over the uterus. Subsequently, the closely apposed walls of
lon, until the differential growth, rotation and circumabdominal dis these deep peritoneal pouches fuse over much of their caudal extent,
placement of this part of the gut tube near completion. Its original their mesothelia are lost, and the viscera are separated by an interven


root is still vertical in the dorsal midline, although the mesocolon ing, bilaminar (surgically separable), fibrous stratum. In the male, this
diverges from it widely as an incomplete, flattened pyramid, to reach becomes the rectovesical fascia and posterior wall of the prostatic
its colonic border at the future taenia mesocolica. During the fourth sheath (see Fig. 72.10). In the female, it becomes the rectovaginal
and fifth months, substantial areas of the primitive mesocolon adhere septum between the lower part of the vagina and the rectum (see Fig.
to, then fuse with, the parietal peritoneum. In this way, some colonic 72.9). The proximal third of the rectum is covered by peritoneum ven
segments become sessile while others have a shorter mesocolon with trolaterally; the lateral extensions of this tunic are triangular and deep
an often profoundly altered parietal line of attachment. The mesoco proximally, but taper to an acute angle by the middle third of the
lon of the transverse and sigmoid segments normally persists, while rectum. The middle third of the rectum is covered by peritoneum only
the ascending colon, right (hepatic) flexure and descending colon on its ventral surface, where it forms the posterior wall of the shallower
become sessile; the ascending or descending, or both, colonic seg rectovesical or rectovaginouterine pouch. The remaining rectum and
ments may also retain a mesocolon, which varies from a localized anal canal are extraperitoneal.
‘fold’ to a complete mesocolon. When sessile, the ventral, medial and
lateral aspects of the ascending or descending colon are clothed with
NEONATAL PERITONEAL CAVITY
peritoneum, and the protrusion of the viscus produces medial and
lateral peritoneal paracolic gutters on each side. This form of apposi
The fully formed peritoneal cavity, although complex topographically,
tion to underlying structures (zygosis) proceeds from the ascending
remains a single cavity with numerous intercommunicating regions,
colon to include the right colic (hepatic) flexure; from there, it contin


pouches and recesses (see Fig. 14.7). The only small peritoneal sacs to
ues anteroinferiorly to the left, so involving the rightsided initial
separate completely from the main cavity are the infracardiac bursa and
segment of the transverse colon.
the tunica vaginalis testis (see Fig. 72.17).
In fetal life, the greater omental cavity extends to the internal
Transverse colon
aspect of the lateral and caudal edges of the omentum. Postnatally, a
The right extremity of the transverse colon is sessile, and is separated
slow but progressive fusion of the internal surfaces occurs, with oblit
by fibroareolar tissue from the anterior aspect of the descending
eration of the most dependent part of the cavity; this proceeds ros
(second) part of the duodenum and the corresponding aspect of most
trally and, when mature, the cavity does not usually extend appreciably
of the head of the pancreas. The remainder of the transverse colon, up
beyond the transverse colon. Transverse mesocolon–greater omentum
to and including the left (splenic) colic flexure, is almost completely
fusion begins early while the umbilical hernia of the midgut has not
peritonealized by the diverging layers of the transverse mesocolon.
returned. It starts between the right margin of the early greater
The root of the latter reaches the neck and whole extent of the ante
omentum and near the root of the presumptive mesocolon, and later
rior border of the body of the pancreas. The long axis of the definitive
spreads to the left.
pancreas lies obliquely. The splenic colonic flexure is considerably
In the neonate, the peritoneal cavity is ovoid (see Fig. 14.6). It is
more rostral than the hepatic flexure and, consequently, the root of
fairly shallow from anterior to posterior because the bilateral posterior
the mesocolon curves obliquely upwards as it crosses the upper
extensions on each side of the vertebral column, which are prominent
abdomen from right to left. As it expands, the posteroinferior wall of
in the adult, are not present. Two factors lead to the protuberance of
the greater omental part of the lesser sac gradually covers, and becomes


the anterior abdominal wall in the neonate and infant. The diaphragm
closely applied to, the transverse mesocolon and its contained colon,
is flatter in the newborn, which produces a caudal displacement of the
finally projecting beyond the latter. Craniocaudal adherence now
viscera. The pelvic cavity is very small in the neonate, which means that
occurs between the omental wall and the pericolonic and mesoco
organs that are normally pelvic in the adult, i.e. urinary bladder, ovaries
lonic layers.
and uterus, all extend superiorly into the abdomen (see Figs 14.7,
72.9–72.10). The pelvic cavity is joined to the abdominal cavity at less
Descending colon
of an acute angle in the neonate because there is no lumbar vertebral
The left colic flexure receives much of its peritoneal covering from the curve and only a slight sacral curve.
left extremity of the transverse mesocolon. It is also often connected The peritoneal attachments are similar to the adult. However, the
to the parietal peritoneum of the diaphragm over the tenth and greater omentum is relatively small; its constituent layers of peritoneum


DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
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may not be completely fused, and it does not extend much below the The most common anomaly of suprarenal gland development is
level of the umbilicus. Generally, the length of the mesentery of the congenital hyperplasia, which occurs in 1 : 5000 to 1 : 15,000 births.
small intestine and of the transverse and sigmoid mesocolons is greater This condition is caused by a group of autosomal recessive disorders,
than in the adult, whereas the area of attachment of the ascending and in which there are deficiencies in enzymes required for the synthesis of
descending colons is relatively smaller. The peritoneal mesenteries and cortisol. In 90% of cases, the cause is deficiency of the enzyme
omenta contain little fat. 21hydroxylase, producing an accumulation of 17hydroxyprogesterone,
which is converted to androgens. The levels of androgens increase by
several hundred times, causing female embryos and fetuses to undergo
SPLEEN
external genital masculinization ranging from clitoral hypertrophy to
formation of a phallus and scrotum; masculinization of the brain has
The spleen appears about the sixth week as a localized thickening of also been suggested. In male embryos, the levels do not cause any
the coelomic epithelium of the dorsal mesogastrium near its cranial end changes in external genitalia. Signs of androgen excess may appear in
(see Figs 60.6–60.7). The proliferating cells invade the underlying ang childhood with precocious masculinization and accelerated growth
iogenetic mesenchyme, which becomes condensed and vascularized. (Lewis et al 1999).
The process occurs simultaneously in several adjoining areas, which
soon fuse to form a lobulated spleen of dual origin (from coelomic
epithelium and from mesenchyme of the dorsal mesogastrium). SUPRARENAL GLANDS IN THE NEONATE
The vascular reticulum is well developed at 8–9 weeks, and contains


immature reticulocytes and numerous closely spaced, thinwalled, vas The suprarenal glands are relatively very large at birth (see Figs 14.6C,
cular loops. From 11 weeks, the development of the spleen has been 72.8) and constitute 0.2% of the entire body weight, compared with
described in four stages: stage 0 has erythrocyte precursors, few macro 0.01% in the adult. The left gland is heavier and larger than the right,
phages and fewer lymphocytes; at stage I, lymphocytes begin coloniza as it is in the adult. At term, each gland usually weighs 4 g; the average
tion and arterial vascular lobules are seen; at stage II, T and B weight of the two glands is 9 g (average in the adult is 7–12 g). Estima
lymphocytes form periarteriolar clusters with B cells aggregated around tion of the suprarenal gland volume can provide an estimate of fetal
the peripheral branches of splenic arterioles and T cells centrally; at weight; a volume of greater than 420 mm3/kg is relevant in predicting
stage III, before birth, the lobular arrangement is no longer discernible preterm birth within 5 days of measurement (Turan et al 2012, Turan
(Steiniger et al 2007). et al 2007). Within the first 2 weeks of postnatal life, the glands shrink
From week 17, αSMApositive reticulum cells are found around to normal infantile size. The average weight of both glands is 5 g by the
arterioles. These increase in number and form a reticular framework end of the second week, and 4 g by 3 months; gland birth weight is not
from 20 to 23 weeks, when a primitive white pulp can be observed regained until puberty. This rapid involution of the glands occurs
around arterioles. By 24 weeks, T and B lymphocytes become segre regardless of gestational age. It is thought that parturition is the stimu
gated, with T cells within the SMApositive reticular framework, and B lus for suprarenal involution (BenDavid et al 2007). The cortex of the


cells aggregating close to the periarticular lymphoid sheath, where they suprarenal gland is thicker than in the adult and the medulla of the
form lymphoid follicles (Satoh et al 2009). gland is small. With normal involution, the fetal zone cells of the post
Initially, the splenic capsule consists of cuboidal cells bearing cilia natal gland become smaller and they assume the appearance and organ
and microvilli. The enlarging spleen projects to the left, so that its sur ization typical of zona fasciculata.
faces are covered by the peritoneum of the mesogastrium on its left
aspect, which forms a boundary of the general extrabursal (greater) sac.
When fusion occurs between the dorsal wall of the lesser sac and the INFERIOR VENA CAVA, PORTAL CIRCULATION
dorsal parietal peritoneum, it does not extend to the left as far as the
AND UMBILICAL VESSELS
spleen, which remains connected to the dorsal abdominal wall by a
short splenorenal ligament. Its original connection with the stomach
persists as the gastrosplenic ligament. The earlier lobulated character of INFERIOR VENA CAVA
the spleen disappears, but is indicated by the presence of notches on
its upper border in the adult. The inferior vena cava of the adult is a composite vessel that develops
The spleen displays various developmental anomalies, including on the posterior abdominal wall dorsal to the developing peritoneal
complete agenesis, multiple spleens or polysplenia, isolated small addi cavity. It forms as a consequence of the temporal remodelling of suc
tional spleniculi and persistent lobulation. Asplenia and polysplenia cessive venous complexes (see Fig. 13.4). The precise mode of develop
are associated with other anomalies, especially those involving the ment of its postrenal segment (caudal to the renal vein) is still somewhat
cardiac and pulmonary systems. Accessory spleens are very common in uncertain. Its function is initially carried out by the right and left post
neonates, located in the greater omentum. At birth, the spleen weighs, cardinal veins (Fig. 60.8; see also Fig. 13.4), which receive the venous


on average, 13 g (see Fig. 14.6). It doubles its weight in the first post drainage of the lower limb buds and pelvis, and run in the dorsal part
natal year and triples it by the end of the third year. of the mesonephric ridges, receiving tributaries from the body wall
(intersegmental veins) and from the derivatives of the mesonephroi. It
should be remembered that descriptions of venous development are
SUPRARENAL GLANDS
very largely based on studies on animals, where the dimensions and
final disposition of visceral organs differ from those found in humans.
The suprarenal (adrenal) cortex is formed during the second month by Many of the changes seen in the development of the infrahepatic caval
a proliferation of the coelomic epithelium. Cells pass into the underly and azygos systems in the human may result from lateral to medial
ing mesenchyme between the root of the dorsal mesogastrium and the movement of the vessels as a consequence of the growth of the abdomi
mesonephros (see Fig. 17.11). The proliferating tissue, which extends nal viscera (Hikspoors et al 2015).
from the level of the sixth to the twelfth thoracic segments, is soon The early postcardinal veins communicate across the midline via an
disorganized dorsomedially by invasion of neural crest cells from interpostcardinal anastomosis. This remains as an oblique transverse
somite levels 18–24, which form the medulla, and also by the develop anastomosis between the iliac veins, and becomes the major part of the
ment of venous sinusoids. The latter are joined by capillaries, which definitive left common iliac vein. It diverts an increasing volume of
arise from adjacent mesonephric arteries and penetrate the cortex in a blood into the right longitudinal veins, which accounts for the ultimate
radial manner. When proliferation of the coelomic epithelium stops, disappearance of most of those on the left.
the cortex is enveloped ventrally, and later dorsally, by a mesenchymal The supracardinal veins receive the larger venous drainage of the
capsule that is derived from the mesonephros. The subcapsular nests of growing body wall. The right supracardinal vein persists and forms


cortical cells are the rudiment of the zona glomerulosa; they proliferate the greater part of the postrenal segment of the inferior vena cava. The
cords of cells that pass deeply between the capillaries and sinusoids. continuity of the vessel is maintained by the persistence of the anasto
The cells in these cords degenerate in an erratic fashion as they pass mosis between the right supracardinal and the right subcardinal in the
towards the medulla, becoming granular, eosinophilic and, ultimately, renal collar. The left supracardinal disappears, but some of the renal
autolysed. These cords of cells constitute the fetal cortex, which under collar formed by the left supracardinal–subcardinal anastomosis per
goes rapid involution during the first 2 years after birth. The fascicular sists in the left renal vein. Both supracardinal veins drain cranially into
and reticular zones of the adult cortex are proliferated from the glomer the subcardinal veins. On the right side, the subcardinal vein comes
ular zone after birth. Serial ultrasound measurements of the length of into intimate relationship with the liver. An extension of the vessel takes
fetal suprarenal glands at 4week intervals from the fifteenth week of place in a cranial direction and meets and establishes continuity with
gestation have been published (van Vuuren et al 2012). a corresponding new formation that is growing caudally from the right


inferior vena cava, portal circulation and umbilical vessels
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Brachiocephalic veins
A B Superior
intercostal vein
Internal jugular veins
Oblique vein
Superior
and ligament
vena cava
of left atrium
Azygos vein IVC hepatic
Postcardinal vein
segment
IVC subhepatic
segment
Hemiazygos vein
IVC subcardinal
Remains of intersubcardinal segment
anastomosis (renal collar)
Left suprarenal vein
Left supracardinal vein Left renal vein
Oblique transverse anastomosis
Left gonadal vein
IVC supracardinal
segment
Postcardinal vein
Supracardinal vein (thoracolumbar line vein) Common iliac veins
Azygos line vein (medial sympathetic line vein)
Subcardinal vein
Hepatic segment of inferior vena cava
(and right vitelline vein)
Subhepatic segment of IVC
Fig. 60.8 The inferior vena cava (IVC) develops within the posterior abdominal wall. It is a composite vessel formed by temporal remodelling of
successive somatic venous anastomoses. A, The progressive asymmetry of the developing venous system. B, The definitive venous arrangement. (For
early venous development, see Fig. 13.4.)
vitelline hepatocardiac (common hepatic) vein. In this way, on the right embryonic arrangement occur with the growth of the foregut, liver and
side, a more direct route is established to the heart and the prerenal paired viscera, i.e. kidneys and suprarenal glands.
(cranial) segment of the inferior vena. In summary, the inferior vena The early development of the ventral splanchnic arteries is outlined
cava is formed from below upwards by the confluence of: the common in Chapter 13. Three main arterial trunks – the coeliac trunk, superior
iliac veins, a short segment of the right postcardinal vein, the mesenteric and inferior mesenteric arteries – supply the fore, mid and
postcardinal–supracardinal anastomosis, part of the right supracardinal hindgut, respectively. From the gastric terminal segment of the future


vein, the right supracardinal–subcardinal anastomosis, right subcardi oesophagus to the upper rectum, the developing endodermal epithe
nal vein, a new anastomotic channel of double origin (the hepatic lium is surrounded by splanchnopleuric mesenchyme permeated by a
segment of the inferior vena cava), and the cardiac termination of the capillary plexus that drains into an anastomosing network of veins. This
right vitelline hepatocardiac vein (common hepatic vein). plexus is particularly dense ventrally where it is associated with the
Only the supracardinal part of the inferior vena cava receives central midgut region; here, for a while, it receives a network of small
intersegmental venous drainage. The postrenal (caudal) segment of the veins from the definitive yolk sac. Later, in normal development, these
inferior vena cava is on a plane that lies dorsal to the plane of the vessels atrophy as the yolk sac diminishes. More rostrally, the splanch
prerenal (cranial) segment. Thus, the right phrenic, suprarenal and nopleuric capillaries associated with the foregut and upper portions of
renal arteries, which represent persistent mesonephric arteries, pass the yolk sac form longitudinal channels anterolateral to the gut and
behind the inferior vena cava, whereas the testicular or ovarian artery, these become increasingly well defined as the embryonic abdominal
which has a similar developmental origin, passes anterior to it. vitelline veins. Entering the septum transversum, the right and left vitel
In some animals, the right postcardinal vein constitutes a large part line veins incline slightly, becoming parallel to the lateral aspects of the
of the postrenal segment of the inferior vena cava. In these cases, the gut. They establish connections with capillary plexuses in the septal
right ureter, on leaving the kidney, passes medially dorsal to the vessel mesenchyme, and then continue, finally curving to enter the medial
and then, curving round its medial side, crosses its ventral aspect. part of the cardiac sinual horn of their corresponding side. The parts of


Rarely, a similar condition is found in humans, and indicates the per the gut closely related to the presinual segments of the vitelline veins
sistence of the right postcardinal vein and failure of the right supracar are the future subdiaphragmatic end of the oesophagus, primitive
dinal to play its normal part in the development of the inferior vena stomach, the superior (first) and descending (second) regions of the
cava. duodenum, and the remainder of the duodenal tube.
The principal ascending vitelline veins flanking the sides of the
abdominal part of the foregut receive venules from its splanchnopleuric
PORTAL CIRCULATION capillaries and those of the septal mesenchyme. Within these venular
nets, enlarged (but still plexiform) anastomoses connect the two vitel
The heart first differentiates in splanchnopleure that, after headfold line veins (Fig. 60.9; see Fig. 13.1C). A subdiaphragmatic intervitelline
formation, forms the dorsal wall of the primitive pericardial cavity anastomosis develops in the rostral septal mesenchyme, lying a little
(floor of the rostral foregut) and may, therefore, be considered a highly caudal to the cardiac sinuatrial chamber, connecting the veins near their
specialized vitelline vascular derivative. At the caudal extremity of the sinual terminations. (The channel is sometimes termed suprahepatic
splanchnopleuric gut tube (the future lower rectum and upper anal because of the position of the hepatic primordium; with expansion of
canal), the vitelline venous drainage makes connections with the inter the latter, it becomes partly intrahepatic.) The presumptive duodenum
nal iliac radicles of the postcardinal complex. is crossed by three transverse duodenal intervitelline anastomoses. Their
The development of the gut occurs contemporaneously with changes relation to the gut tube alternates so that the most cranial, the subhe
to the early symmetrical embryonic circulation (Ch. 13). A symmetrical, patic, is ventral, the intermediate is dorsal and the caudal is ventral (Fig.


segmental system of somatic arteries remains and supplies the body 60.9B). It has become customary to describe the paraduodenal vitelline
wall of the trunk. The underlying arrangement of these vessels is only veins and their associated anastomoses as forming a figure eight. At this
slightly modified by subsequent development. The main changes to the early stage, when left and right embryonic veins are still symmetrical,


DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
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A Common sinuatrial chamber B Parts that persist, expand and
modify into main permanent
Sinus venosus: right horn channels
Right New connections forming further main
precardinal vein permanent channels
Site of hepatic rudiment, which expands
Right common
cardinal vein INTERVITELLINE and invades neighbouring anastomoses,
ANASTOMOTIC vitelline and umbilical veins
Right VEINS
postcardinal vein 1 Subdiaphragmatic Oxygenated blood
(suprahepatic)
Early ductus venosus Deoxygenated blood
Right 2 Subhepatic, ventral
Right vitelline duodenal
umbilical vein vein
3 Intermediate, dorsal
Region of future duodenal
duodenum
4 Caudal, central
duodenal
Fig. 60.9 Development of the vitelline, umbilical and terminal cardinal vein complexes: the early symmetrical condition. A, The early symmetrical
arrangement of cardinal and umbilical veins entering the sinus venosus; blood from the yolk sac passes, via vitelline veins, through anastomoses forming
in the septum transversum mesenchyme (green). B, The developing duodenum is surrounded by transverse duodenal intervitelline anastomoses.
Changes in the developing gut and umbilical veins cause shifts in the routes taken by venous blood flowing to the sinus venosus.
Right half of subdiaphragmatic anastomosis
Progressive inflection of sinuatrial wall
Right precardinal and common cardinal veins
Left precardinal and common cardinal veins
Right postcardinal vein Postcardinal vein
Hepatocardiac part of right umbilical vein
Hepatocardiac part of left umbilical vein
Left venae revehentes
Right hepatocardiac vein (termination of Hepatocardiac part of left vitelline vein
right vitelline vein – future inferior vena cava)
Hepatic terminals of left vitelline vein
Left venae advehentes
Hepatic terminal right umbilical vein Hepatic terminals of left umbilical vein


Vitelline vein segments and ventral anastomosis New venous connections
Left umbilical vein
Presumptive splenic vein Merge to form root of
Presumptive superior mesenteric vein definitive hepatic portal vein
Parts that persist, expand and modify into
main permanent channels
New connections forming further main permanent channels
Oxygenated blood
Deoxygenated blood
Fig. 60.10 Development of the vitelline, umbilical and terminal cardinal vein complexes: a mid-stage of asymmetry has been reached between the early
symmetrical condition (see Fig. 60.9) and the definitive late prenatal state. The extent of the liver within the septum transversum mesenchyme is shown
in green.
the cranial duodenal anastomosis becomes connected with the subdia CHANGES IN THE VITELLO-UMBILICAL VEINS
phragmatic anastomosis by a median longitudinal channel, the primi
tive median ductus venosus, which is dorsal to the expanding hepatic Progressive changes in the vitelloumbilical veins are rapid, profound
primordium but ventral to the gut. The further development of the and closely linked with regional modifications in shape and position
vitelline veins and anastomoses is, as indicated, closely interlocked, of the gut, expansion and invasion of venous channels by hepatic tissue,
with rapid hepatic expansion and gut changes, and umbilical vein dis asymmetry of the heart and cardiac venous return. The principal events
position and modification is closely involved. are summarized in Figures 60.9–60.11.


inferior vena cava, portal circulation and umbilical vessels
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Superior vena cava Left atrium Fig. 60.11 The condition of some main upper
abdominal and intrathoracic right atrial terminal
Coronary sinus
veins in the later prenatal months. The rotation of
Right atrium Secondary upper left hepatic vein the stomach and movement of the duodenum
produce relative changes in the final arrangement
Inferior vena cava of the duodenal intervitelline anastomoses that
form the hepatic portal vein.
Upper right hepatic vein
Ductus venosus
Lower right hepatic vein
Persistent left afferent hepatic veins
Left umbilical vein
Portal vein formed from the
Splenic vein
final arrangement of anterior,
left and posterior anastomoses
around the duodenum Superior mesenteric vein
Duodenum
Oxygenated blood
Deoxygenated blood
From the cranial portion of the early hepatic evagination of the fibrous tags attached to the inferior wall of the coronary sinus. The right
foregut, interconnected sheets and ‘cords’ of endodermal cells, the pre vitelline hepatocardiac vein continues enlarging and, ultimately, forms
sumptive hepatocytes, penetrate the septum transversum mesenchyme. the terminal segment of the inferior vena cava. The latter receives the
Hepatic mesenchyme is composed of a mixed population of cells with right efferent hepatic veins and new channels draining the territories of
endothelial/angiogenic and connective tissue lineages. Capillary plex the left efferent hepatic veins. These collectively form the upper and
uses develop within this mesenchyme and, possibly under the influence lower groups of right and (secondary) left hepatic veins. The terminal
of the endodermal hepatic sheets, the plexuses become more profuse caval segment also shows the orifice of the right half of the intervitelline
by further addition of angioblastic septal mesenchyme, which also subdiaphragmatic anastomosis, and a large new connection with the
forms masses of perivascular intrahepatic haemopoietic tissue. These right subcardinal vein.
processes extend along the plexiform connections of the vitelline, and The hepatic terminals of the right and left duodenal parts of the


later the umbilical, veins until their intrahepatic (transseptal) zones vitelline veins are destined to form the corresponding branches of the
themselves become largely plexiform. Initially capillary in nature, they hepatic portal vein, the left branch incorporating the cranial ventral
transform into a mass of rather wider, irregular, sinusoidal vessels with intervitelline anastomosis. With rotation of the gut and formation of
a discontinuous endothelium containing many phagocytic cells. The the duodenal loop, segments of the original vitelline veins and the
lengths of vitelline veins involved in these processes are the intermedi caudal transverse anastomosis atrophy (indicated in Figs 60.10–60.11),
ate parts of the segments extending from the subhepatic (cranioventral while new splanchnopleuric venous channels – the superior mesenteric
duodenal) to the suprahepatic (subdiaphragmatic) transverse intervitel and splenic veins – converge and join the left end of the dorsal inter
line anastomoses, and the corresponding lengths of the umbilical veins. mediate anastomosis. The numerous other radicles of the portal vein
Thus, at this early stage, the liver sinusoids are perfused by mixed blood and its principal branches, including the inferior mesenteric vein, are
reaching them through a series of branching vessels collectively called later formations.
the venae advehentes, or afferent hepatic veins: they are deoxygenated For a period, placental blood returns from the umbilicus via right
from the gut splanchnopleure via vitelline vein hepatic terminals, and and left umbilical veins, both discharging through afferent hepatic veins
oxygenated from the placenta via hepatic terminals of the umbilical into the hepatic sinusoids, where admixture with vitelline blood occurs.
veins (see Fig. 60.10). Blood leaves the liver through four venae reve At approximately 7 mm crown–rump length, the right umbilical vein
hentes (efferent hepatic veins); two on each side reach and open into retrogresses completely. The left umbilical vein retains some vessels
their respective cardiac sinual horns. This full complement of four discharging directly into the sinusoids, but new enlarging connections


hepatocardiac veins is only transient and becomes reduced to one with the left half of the subhepatic intervitelline anastomosis emerge.
dominant, rapidly enlarging channel. The originally bilaterally sym The latter is the start of a bypass channel for the majority of the pla
metrical cardinal vein complexes, both rostral and caudal, develop cental blood, which continues through the median ductus venosus and,
transverse or oblique anastomoses so that the cardiac venous return is finally, the right half of the subdiaphragmatic anastomosis, to reach the
ultimately restricted to the definitive right atrium. termination of the inferior vena cava (see Fig. 60.11).
These cardiac and concomitant hepatoenteric changes are accompa The left and right hepatic portal veins and the ductus venosus are
nied by events in supra, intra and subhepatic parts of the vitello routinely observed in the second trimester ultrasound scan at the plane
umbilical veins. Some vessels enlarge, persisting as definitive vessels to to estimate abdominal circumference (see Fig. 14.4G).
maturity; in places, they are joined later by other channels that become
defined in already established capillary plexuses. Other vessels retro
FETAL/NEONATAL UMBILICAL VESSELS
gress, either disappearing completely or remaining as vestigial tags and,
occasionally, vessels of fine calibre. Some vessels of crucial importance
Umbilical arteries
in the circulatory patterns of embryonic and fetal life become obliter
ated postnatally and transformed to substantial fibrous cords. Both
right and left umbilical hepatocardiac and the left vitelline hepatocar The fetal umbilical arteries are in direct continuation with the internal
diac veins continue, for a time, to discharge blood into their sinual iliac arteries. Their lumen is 2–3 mm in diameter at their origin, when
horns; however, they begin to retrogress (see Figs 60.9–60.10). The right distended. This narrows as they approach the umbilicus, where there is
umbilical channel atrophies completely. The left channels also disap a reciprocal thickening of the tunica media, as a result, in particular, of


pear, but their cardiac terminals may, on occasion, be found as conical an increase in the number of longitudinal smooth muscle fibres and


DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
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Table 60.1 Key anatomical reference points for umbilical arterial catheterization Umbilical vein
Structure Vertebral level
The umbilical vein in the neonate is 2–3 cm long and 4–5 mm in
Ductus arteriosus T4–5
diameter when distended. It passes from the umbilicus, within the layers
Coeliac artery T12 of the falciform ligament, superiorly and to the right, to the porta hepatis.
Superior mesenteric artery T12–L1 Here, it gives off several large intrahepatic branches to the liver and then
Renal artery L1 joins the left branch of the portal vein and the ductus venosus. The
Inferior mesenteric artery L3 umbilical vein is thinwalled; it possesses a definite internal lamina of
Aortic bifurcation L4–5 elastic fibres at the umbilical ring but not in its intraabdominal course.
The tunica media contains smooth muscle fibres, collagen and elastic
fibres. When the cord is severed, the umbilical vein contracts, but not
elastic fibres. Before birth, there is a proliferation of connective tissue so vigorously as the arteries. The rapid decrease in pressure in the umbili
within the vessel wall. The umbilical vessels constrict in response to cal vein after the cord is clamped means that the elastic tissue at the
handling, stretching, cooling and altered tensions of oxygen and carbon umbilical ring is sufficient to arrest any retrograde flow along the vessel.
dioxide. Umbilical vessels are muscular, but devoid of a nerve supply Before birth, there is a subintimal proliferation of connective tissue.
in their extraabdominal course. After the cord is severed, the umbilical After birth, the contraction of the collagen fibres in the tunica media
arteries contract, preventing significant blood loss; thrombi often form and the increased subintimal connective tissue contribute to the trans
in the distal ends of the arteries. The arteries obliterate from their distal formation of the vessel into the ligamentum teres. Obliteration occurs


ends until, by the end of the second or third postnatal month, involu from the umbilical ring towards the hepatic end. No thrombi are formed
tion has occurred at the level of the superior vesical arteries. The proxi in the obliteration process. For up to 48 hours after birth, the intra
mal parts of the obliterated vessels remain as the medial umbilical abdominal portion of the umbilical vein can be easily dilated. In most
ligaments. adults, the original lumen of the vein persists through the ligamentum
teres and can be dilated to 5–6 mm in diameter.
Umbilical arterial catheterization
Insertion of an umbilical catheter is undertaken to provide direct access Ductus venosus
to the arterial circulation. Arterial blood can be withdrawn repeatedly The ductus venosus is a direct continuation of the umbilical vein and
for measurement of oxygen and carbon dioxide partial pressures, pH, arises from the left branch of the portal vein, directly opposite the
base excess and many other parameters of blood biochemistry and termination of the umbilical vein. It passes for 2–3 cm within the layers
haematology. The indwelling catheter also enables the continuous of the lesser omentum, in a groove between the left lobe and caudate
measurement of arterial blood pressure. lobe of the liver, before terminating in either the inferior vena cava, or
The catheter is inserted directly into either the cut end or the side of in the left hepatic vein immediately before it joins the inferior vena
one of the two umbilical arteries in the umbilical cord stump that cava. The tunica media of the ductus venosus contains circularly
remains attached to the baby after transection of the umbilical cord at arranged smooth muscle fibres, an abundant amount of elastic fibres
the time of delivery. The catheter tip is then advanced along the length and some connective tissue.
of the umbilical artery, through the internal iliac artery, into the The ductus venosus is already closed in about onethird of newborn
common iliac artery and, from there, into the aorta. In order to keep infants. It shuts down by an unknown mechanism. Obliteration begins
the catheter patent, a small volume of fluid is continuously infused at the portal vein end in the second postnatal week and progresses to


through it. It is important for the tip of the catheter to be located well the vena cava; the lumen has been completely obliterated by the second
away from arteries branching from the aorta, to avoid potentially or third month after birth. The fibrous remnant of the ductus venosus
harmful perfusion of these arteries with the catheter fluid. Thus, umbili is the ligamentum venosum.
cal arterial catheter tips are placed in the descending aorta either in a
Umbilical vein catheterization
‘high’ position, above the coeliac artery but well below the ductus arte
riosus, or in a ‘low’ position, below the renal and inferior mesenteric The umbilical vein may be catheterized in the neonate to enable
arteries but above the point where the aorta bifurcates into the two exchange and transfusion of blood, for central venous pressure meas
common iliac arteries. The length of catheter to be inserted can be urement and, usually in an emergency, for vascular access. The catheter
estimated from charts relating the required catheter length to external is inserted into the cut end of the umbilical vein and is advanced along
body measurements, or from birth weight. Positioning of the catheter the length of the vein, through the ductus venosus and into the inferior
is assessed by means of radiographs of the abdomen or chest: a ‘high’ vena cava; the tip is placed between the ductus venosus and the right
catheter tip should be located in the descending aorta somewhere atrium. Positioning of the catheter tip is confirmed radiologically and
between the levels of the sixth and ninth thoracic vertebrae (T6–9), it should be located just above the diaphragm at a point that is level
while a ‘low’ catheter tip should be at a level between the third and with the ninth or tenth thoracic vertebra (T9/T10). As with umbilical
fourth lumbar vertebrae (L3–4). Relevant anatomical reference points arterial catheters, estimation of the required catheter length can be
are given in Table 60.1. determined from standard charts.
KEY REFERENCES
Collins P 2002a Embryology of the pancreas. In: Howard ER, Stringer MD, Lebenthal E 1989 Concepts in gastrointestinal development. In: Lebenthal


Colombani PM (eds) Surgery of the Liver, Bile Ducts and Pancreas in E (ed) Human Gastrointestinal Development. New York: Raven Press;
Children, Part 8. London: Arnold, pp. 479–92. Ch. 1.
Covers pancreatic morphogenesis, the timescale of development, the origin of This chapter is the first in a volume dedicated to the development of
pancreatic cell lines and factors that regulate pancreatic development. structure and function of the gut, liver and pancreas. It includes the
development of the immunological surveillance mechanisms and
Collins P 2002b Embryology of the liver and bile ducts. In: Howard ER, gastrointestinal flora.
Stringer MD, Colombani PM (eds) Surgery of the Liver, Bile Ducts and
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Gershon MD 2010 Developmental determinants of the independence and O’Rahilly R, Müller F 1987 Developmental Stages in Human Embryos.
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Howard ER 2002 Biliary atresia: aetiology, management and complications.
In: Howard ER, Stringer MD, Colombani PM (eds) Surgery of the Liver, Whittle MJ 1999 Gastrointestinal abnormalities. In: Rodeck CH, Whittle MJ
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congenital, infective and anatomical factors that are related to the condition.


Development of the peritoneal cavity, gastrointestinal tract and its adnexae
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Covers pancreatic morphogenesis, the timescale of development, the origin of maturation of the gut.
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CHAPTER
61
Anterior abdominal wall
The anterior abdominal wall constitutes a hexagonal area defined supe- adherent to the linea alba and pubic symphysis. Inferiorly, it fuses
riorly by the costal margins and xiphoid process, laterally by the mid- with the iliac crest, extends superficial to the inguinal ligament and
axillary line, and inferiorly by the iliac crests, pubis and pubic symphysis. fuses with the fascia lata at the inguinal flexure or skin crease of the
It is continuous with the posterior abdominal wall and paravertebral thigh. In the male, it extends on to the dorsum of the penis, forming
tissues, forming a flexible sheet of skin, muscle and connective tissue part of the superficial ligament of the penis, and on to the scrotum,
across the anterior and lateral aspects of the abdomen. These tissues where it becomes continuous with the membranous layer of superfi-
also form the umbilicus and the inguinal canal, which connects the cial fascia of the perineum (Colles’ fascia). In the female, it continues
abdominal cavity to the scrotum in men or to the labia majora in into the labia majora and is continuous with the fascia of the
women. The anterior abdominal wall maintains the shape of the perineum.
abdomen and aids numerous physiological functions. However, its In boys, the testis can frequently be retracted out of the scrotum into
dysfunction is equally notable because hernia repair is the single most the loose areolar tissue between the membranous layer of superficial
common operation performed by general surgeons. fascia over the inguinal canal and the external oblique aponeurosis. This
‘space’ is sometimes called the superficial inguinal pouch.
Deep adipose layer
SKIN AND SOFT TISSUE
The thickness of the deep adipose layer is more variable than the super-
ficial fatty layer. It is thin or absent where the membranous layer fuses
The integument of the anterior abdominal wall comprises skin, soft with bony prominences and the linea alba, and becomes markedly
tissues, and lymphatic and vascular structures, as well as segmental thick in the morbidly obese. Its adipocytes show different metabolic


nerves. The outer layer is formed from the skin and subcutaneous fat. activities to those in the superficial adipose layer (Chopra et al 2011).
The skin is non-specialized and variably hirsute, depending on sex and Liposuction preferentially removes this layer of fat with relative preser-
race. All postpubertal individuals have some extension of the pubic hair vation of the superficial adipose layer in order to avoid skin dimpling
on to the anterior abdominal wall skin, although this is commonly and other skin contour irregularities (Markman and Barton 1987).
most pronounced in males, in whom the hair may extend almost up
to the umbilicus in a triangular pattern. The subcutaneous fat of the
abdominal wall is highly variable in thickness, depending in part on Transversalis fascia
gender and adiposity.
The transversalis fascia is a thin layer of connective tissue lying between
the deep surface of transversus abdominis and the extraperitoneal fat.
SOFT TISSUE
It is part of the general layer of thin fascia between the peritoneum and
the abdominal wall. Posteriorly, it fuses with the anterior layer of the
Superficial fascia
thoracolumbar fascia (p. 1083), and anteriorly, it forms a continuous
sheet. Superiorly, it blends with the fascia covering the inferior surface
The ‘superficial fascia’ of the abdominal wall lies between the dermis of the diaphragm. Inferiorly, it is continuous with the iliac and pelvic
and the muscles, and is conventionally divided into a superficial fatty parietal fasciae, and is attached to the iliac crest between the origins
layer (Camper’s fascia) and a deep membranous layer (Scarpa’s fascia). of transversus abdominis and iliacus, and to the posterior margin of
In reality, there are three layers, with a further layer of adipose tissue the inguinal ligament between the anterior superior iliac spine and the
deep to the membranous layer (Lancerotto et al 2011). These three femoral sheath. Medial to the femoral sheath it is thin and fused to the
layers are particularly well defined in the child. Lying within the super- pubis behind the conjoint tendon. An inferior extension of the trans-


ficial fascia are blood vessels, lymphatics, nerves and, in the region of versalis fascia forms the anterior part of the femoral sheath. The fascia
the groin, superficial inguinal lymph nodes. displays a discrete thickening known as the iliopubic tract (also called
the deep crural arch), which runs parallel to the inguinal ligament
Superficial adipose layer
(Teoh et al 1999); it consists of transverse fibres that fan out laterally
The superficial layer contains a variable amount of fat that is partitioned towards the anterior superior iliac spine to blend with the iliopsoas
by fibrous septa connecting the dermis with the deeper membranous fascia and run medially behind the conjoint tendon to the pubic bone.
layer. Inferiorly, it is continuous with the superficial fascia of the thigh, The iliopubic tract is recognized as an important structure during open
and medially, it is continuous over the linea alba. In the male, this layer and laparoscopic inguinal hernia repair. A further thickening of the
continues over the external genitalia, where it becomes thin and pale transversalis fascia, the interfoveolar ligament, runs inferior to the
red, and contains very little adipose tissue. In the scrotum it also con- inguinal ligament at the medial margin of the deep inguinal ring; it
tains the smooth muscle fibres of the dartos muscle. In the female, it may contain muscle fibres.
continues from the suprapubic region of the abdomen into the labia The transversalis fascia is prolonged as the internal spermatic fascia
majora and perineum. over the structures that pass through the deep inguinal ring (the testicu-
lar vessels and vas (ductus) deferens in the male and the round ligament
Membranous layer of the uterus in the female).
The membranous layer is a variably developed entity composed of
connective tissue and elastic fibres. In the adult, its thickness varies
Extraperitoneal connective tissue
over the anterior abdominal wall, becoming thinner in the upper
abdomen (Lancerotto et al 2011). Measured histologically, it is between
0.5 and 1 mm thick but it appears thicker on computed tomography The extraperitoneal connective tissue lying between the peritoneum and


(CT) scans (Lancerotto et al 2011, Chopra et al 2011). It is loosely con- the fasciae lining the abdominal and pelvic cavities contains a variable
nected to the underlying external oblique aponeurosis and rectus amount of fat. The fat is especially abundant on the posterior wall of
sheath by oblique fibrous septa. Superiorly, it is continuous with the the abdomen around the kidneys (particularly in obese men) and
superficial fascia over the remainder of the trunk. In the midline, it is scanty above the iliac crest and in much of the pelvis. 1069


Anterior AbdominAl wAll
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Superficial vessels Deep vessels
Subclavian artery and vein
Internal thoracic artery and vein
Intercostal artery and vein
Axillary vein
Lateral thoracic vein
Musculophrenic artery and vein
Superior epigastric artery and vein
Thoracoepigastric vein
Subcostal artery and vein
Inferior epigastric artery and vein
Superficial epigastric artery and vein
Deep circumflex iliac artery and vein
Superficial circumflex iliac artery and vein
External iliac artery and vein
Superficial external pudendal artery and vein
Femoral artery and vein
Long (great) saphenous vein
Fig. 61.1 The blood supply of the anterior abdominal wall.
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE artery also gives small branches to the anterior part of the diaphragm.
On the right, small branches reach the falciform ligament, where they
Understanding the blood supply of the abdominal wall is critical when anastomose with branches from the hepatic artery.
planning incisions, raising myocutaneous flaps and reconstructing the
abdominal wall during ventral hernia repair (Fig. 61.1).
Inferior epigastric artery and veins
Superior epigastric artery and veins
The inferior epigastric artery (often referred to as the deep inferior
The superior epigastric artery is a terminal branch of the internal tho- epigastric artery in clinical practice in order to distinguish it from the
racic artery. It arises at the level of the sixth costal cartilage and descends superficial (inferior) epigastric artery) originates from the medial aspect
between the costal and xiphoid slips of the diaphragm, accompanied of the external iliac artery just proximal to the inguinal ligament (see
by two or more veins that drain to the internal thoracic vein (see Figs 61.1–61.2; Fig. 61.3). Its accompanying veins, usually two, unite
Fig. 61.1; Fig. 61.2). The vessels pass anterior to the lower fibres of to form a single vein that drains into the external iliac vein (Rozen et al


transversus thoracis and the upper fibres of transversus abdominis 2009). It curves forwards in the anterior extraperitoneal tissue and
before entering the rectus sheath, where they run inferiorly behind ascends obliquely along the medial margin of the deep inguinal ring.
rectus abdominis. They anastomose with the inferior epigastric arteries, It lies posterior to the spermatic cord, separated from it by the transver-
usually above the level of the umbilicus, in one of several potential salis fascia. It pierces the transversalis fascia and enters the rectus sheath
branching patterns (Rozen et al 2008). by passing anterior to the arcuate line. In this part of its course, it is
Branches supply rectus abdominis and perforate the anterior lamina visible through the parietal peritoneum of the anterior abdominal wall
of the rectus sheath to supply the abdominal skin. A branch given off and forms the lateral umbilical fold. Disruption of the artery at this site
in the upper rectus sheath passes anterior to the xiphoid process of the by surgical incisions (e.g. insertion of laparoscopic ports or abdominal
sternum and anastomoses with a corresponding contralateral branch. drains) may result in a haematoma that can expand to considerable size
This vessel may give rise to bleeding during surgical incisions that because of the absence of adjacent tissue against which the bleeding
extend up to and alongside the xiphoid process. The superior epigastric can be tamponaded.


Anterior abdominal wall
1070.e1
16
retPAHC
The vascular supply to the anterior abdominal wall can be divided
into three zones. Zone I represents the epigastrium and central anterior
abdominal wall within the region of rectus abdominis, and is supplied
by the superior and inferior epigastric vessels. Zone II consists of the
lower anterior abdominal wall below zone I and is predominantly
supplied by the superficial epigastric, superficial external pudendal,
and superficial circumflex iliac arteries. Zone III is lateral to zone I and
is supplied by the musculophrenic, lower intercostal, subcostal and
lumbar arteries.
The distance of the vertically running superior and deep inferior
epigastric vessels from the midline is relevant to siting surgical incisions
(Table 61.1).
Table 61.1 Distances of superior and deep inferior epigastric arteries from midline
Level Left Right
Xiphoid cartilage 4.5 ± 0.1 cm 4.4 ± 0.1 cm
Between xiphoid and umbilicus 5.4 ± 0.2 cm 5.5 ± 0.2 cm
Umbilicus 5.6 ± 0.1 cm 5.9 ± 0.1 cm
Between umbilicus and pubic symphysis 5.3 ± 0.1 cm 5.3 ± 0.1 cm
Pubic symphysis 7.5 ± 0.1 cm 7.5 ± 0.1 cm
Adapted from Saber AA, Meslemani AM, Davis R, Pimentel R 2004 Safety zones for anterior abdominal wall
entry during laparoscopy: a CT scan mapping of epigastric vessels. Ann Surg 239:182–5.


Skin and soft tissue
1071
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retPAHC
Fig. 61.2 The deep muscles and
arterial supply of the anterolateral
abdominal wall. The greater part of
Internal thoracic artery and vein Serratus anterior the left rectus abdominis has been
removed to show the superior and
inferior epigastric vessels.
Latissimus dorsi
Superior epigastric
artery and vein
Intercostal artery
Innermost intercostal
Linea alba Musculophrenic artery
Rectus abdominis (cut) External oblique (cut)
Cut edge of aponeurosis Internal oblique (cut)
of internal oblique
Transversus abdominis
Arcuate line Deep circumflex iliac artery
Transversalis fascia
Inferior epigastric artery and vein
Inguinal ligament
Superficial epigastric artery and vein External iliac artery and vein
Rectus abdominis (cut) Deep circumflex iliac artery
Inferior epigastric artery and vein
Pyramidalis Superficial epigastric artery and vein
Spermatic cord
Femoral artery and vein
The inferior epigastric arteries ascend and anastomose with their laparoscopic inguinal hernia repair or with pelvic fractures. Muscular
superior counterpart without branching in about 30% of cases branches supply the abdominal muscles and peritoneum, and anasto-
(El-Mrakby and Milner 2002). Branching into two vessels before anas- mose with the circumflex iliac and lumbar arteries. Cutaneous branches
tomosis is the most common pattern, accounting for almost 60% of perforate the aponeurosis of external oblique, supply the skin and
cases, with a trifurcation being present in the remainder. The inferior anastomose with branches of the superficial epigastric artery. These
epigastric arteries have an average diameter of approximately 3 mm musculocutaneous perforators have been mapped in detail because they
at their origin, compared to an average diameter of 1.6 mm at the are particularly important to plastic surgeons undertaking reconstruc-
origin of the superior epigastric arteries, presumably explaining why the tive surgery with (myo)cutaneous flaps (Rozen et al 2008).


inferior epigastric arteries provide the ‘dominant’ supply to rectus Occasionally, the inferior epigastric artery arises from the femoral
abdominis. Preliminary ligation of the inferior epigastric artery is often artery. It then ascends anterior to the femoral vein to follow its usual
performed when preparing a myocutaneous flap using the mid or lower abdominal course. Rarely, it arises from the external iliac artery in
rectus abdominis based on the superior epigastric artery; this encour- common with an aberrant obturator artery or from the obturator artery.
ages the augmentation of the superior epigastric arterial supply. The superior and inferior epigastric arteries are important sources of
Branches of the inferior epigastric artery anastomose with branches collateral blood flow between the internal thoracic artery and the exter-
of the superior epigastric artery within the rectus sheath posterior to nal iliac artery when aortic blood flow is compromised. Small tributar-
rectus abdominis at a variable level above the umbilicus (Rozen et al ies of the inferior epigastric vein draining the skin around the umbilicus
2008). Other branches anastomose with terminal branches of the lower anastomose with terminal branches of the umbilical vein draining the
five posterior intercostal, subcostal and lumbar arteries at the lateral umbilical region via the falciform ligament. These portosystemic anas-
border of the rectus sheath. Inferolaterally, branches anastomose with tomoses may open widely in cases of portal hypertension, when portal
the deep circumflex iliac artery. The inferior epigastric artery ascends venous blood may drain into the systemic circulation via the inferior
along the medial margin of the deep inguinal ring. The vas deferens in epigastric veins. The pattern of dilated superficial veins radiating from
the male, or the round ligament in the female, passes medially after the umbilicus is referred to as the ‘caput medusae’.
hooking around the artery at the deep inguinal ring. The artery forms
the lateral border of Hesselbach’s inguinal triangle, an important land-
Posterior intercostal, subcostal
mark in laparoscopic inguinal hernia repair; the inferior border of the
and lumbar arteries


triangle is formed by the inguinal ligament, and the medial border is
formed by the lateral margin of rectus abdominis.
The inferior epigastric artery also gives off the cremasteric artery, a The tenth and eleventh posterior intercostal arteries, the subcostal
pubic branch, and muscular and cutaneous branches. The cremasteric artery, and the lumbar arteries pierce the posterior aponeurosis of trans-
artery accompanies the spermatic cord in males, supplies cremaster and versus abdominis to enter the neurovascular plane of the abdominal
the other coverings of the cord and anastomoses with the testicular wall deep to internal oblique (Fig. 61.4). The location of these arteries
artery. In females, the artery is small and accompanies the round liga- and their accompanying segmental nerves is of clinical importance
ment. A pubic branch, near the femoral ring, descends posterior to the when creating myofascial flaps during abdominal wall reconstruction.
pubis and anastomoses with the pubic branch of the obturator artery. The arteries on either side run forwards, giving off muscular branches
The pubic branch of the inferior epigastric artery may be larger than the to the overlying internal and external oblique, before anastomosing
obturator artery and supply most of the obturator artery territory in the with the lateral branches of the superior and inferior epigastric arteries
thigh, in which case it is referred to as the aberrant obturator artery (Pai at the lateral border of the rectus sheath (see Fig. 61.4). Perforating
et al 2009). It lies close to the medial border of the femoral ring and cutaneous vessels run vertically through the muscles to supply the
may be damaged in medial dissection of the ring during femoral or overlying skin and subcutaneous tissue. A small contribution to the


Anterior AbdominAl wAll
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noitCeS
A lower abdominal wall run with the deep circumflex iliac and inferior
epigastric arteries to external iliac nodes.
Inguinal ligament Testicular vessels
Rectus SEGMENTAL NERVES
abdominis
The ventral rami of the sixth to eleventh intercostal nerves, the subcostal
nerve (twelfth thoracic) and first lumbar nerve (iliohypogastric and
Deep ilioinguinal nerves) supply the muscles and skin of the anterior abdom-
inguinal ring inal wall (Rozen et al 2008). The seventh to the twelfth thoracic ventral
rami continue anteriorly from the intercostal and subcostal spaces into
Iliopsoas
the abdominal wall (Fig. 61.5). Approaching the costal margin, the
Femoral seventh to tenth nerves curve medially across the deep surface of
nerve the costal cartilages between the digitations of the diaphragm and
Inferior transversus abdominis. The subcostal nerve gives a branch to the first
External
epigastric
iliac lumbar ventral ramus (dorsolumbar nerve) that contributes to the
vessels
vessels lumbar plexus (Ch. 62). It accompanies the subcostal vessels along the
Femoral ring
inferior border of the twelfth rib, passing behind the lateral arcuate liga-
ment and kidney, and anterior to the upper part of the quadratus
lumborum.
Vas
All these segmental nerves run anteriorly within a thin layer of fascia
deferens
Obturator in the neurovascular plane between transversus abdominis and internal
nerve and oblique, where they branch and interconnect with adjacent nerves
artery (Rozen et al 2008). Muscular branches innervate transversus abdominis
and internal and external oblique. Cutaneous branches supply the
skin of the lateral and anterior abdominal walls. The thoracic nerves
enter the rectus sheath at its lateral margin and pass posterior to
rectus abdominis, where they again intercommunicate. Each nerve then
II
pierces rectus abdominis from its posterior aspect and gives off muscu-
H lar branches to this muscle (and a branch to pyramidalis from the


subcostal nerve), and cutaneous branches that pierce the anterior rectus
sheath to supply overlying skin.
The ninth intercostal nerve supplies skin above the umbilicus, the
tenth supplies skin that consistently includes the umbilicus, and the
eleventh supplies skin below the umbilicus (see Fig. 16.10; Fig. 61.5).
The subcostal nerve supplies the anterior gluteal skin just below the
iliac crest, and the skin of the lower abdomen and inguinal region
(overlapping with the L1 dermatome in this region) (Lee et al 2008).
A typical dermatome map of the anterior abdominal wall is shown in
TT DD Figure 16.10. The ventral rami of the lower intercostal and subcostal
EE
nerves also provide sensory fibres to the costal parts of the diaphragm
and parietal peritoneum.
The transversus abdominis plane (TAP) block is a regional anaes-
B
thetic technique for abdominal surgery. Using ultrasound imaging guid-
ance, local anaesthetic is injected into the neurovascular plane between
Fig. 61.3 A, The deep aspect of the lower part of the anterior abdominal internal oblique and transversus abdominis, targeting the segmental
wall of the left side. The femoral and deep inguinal rings are displayed, nerves of the anterolateral abdominal wall.
together with the vessels and other structures in relation to them and also
the opening into the obturator canal. B, A laparoscopic view showing the Lesions of the intercostal nerves
parietal peritoneum covering the area. Abbreviations: D, vas (ductus)
deferens; E, external iliac vessels; H, orifice of direct inguinal hernia;
I, inferior epigastric vessels; T, testicular vessels. (B, With permission from The anterolateral abdominal wall muscles are innervated by several
Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd segmental nerves and injury to a single nerve does not produce a clini-
ed, Elsevier, Churchill Livingstone. Copyright 2010.) cally detectable loss of muscle tone. The overlap between sequential
dermatomes means that significant cutaneous anaesthesia is appreci-


ated only after sectioning at least two sequential nerves.
supply of the lower abdominal muscles comes from branches of the MUSCLES
deep circumflex iliac arteries.
The anterior abdominal wall is also supplied by branches of the ANTEROLATERAL MUSCLES OF THE ABDOMEN
femoral artery: namely, the superficial epigastric, superficial circumflex
iliac, and superficial external pudendal arteries, and by the deep circum-
Rectus abdominis, pyramidalis, external oblique, internal oblique and
flex iliac artery arising from external iliac artery (see Fig. 78.7A).
transversus abdominis constitute the anterolateral muscles of the
abdomen. They act together to perform a range of functions, some of
Lymphatic drainage
which involve the generation of a positive pressure within one or more
body cavity. Although many of these activities may occur with no
Superficial lymphatic vessels accompany the subcutaneous blood ‘forced assistance’, expiration, defecation and micturition may be aided
vessels immediately below the dermis (Tourani et al 2013). Vessels from by the generation of a positive intra-abdominal pressure. Parturition,
the lumbar and gluteal regions run with the superficial circumflex iliac coughing and vomiting always require such a positive pressure. Under
vessels, and those from the infra-umbilical skin run with the superficial resting conditions, the tone developed within the muscles provides
epigastric vessels. Both drain into superficial inguinal nodes. The supra- support for the abdominal viscera and retains the normal contour of
umbilical region is drained by vessels draining to axillary and paraster- the abdomen. The consequences of diminished muscular support can
nal nodes. be seen in patients who have massive ventral hernias or conditions like
The deep lymphatic vessels accompany the deeper arteries. Laterally, ‘prune belly syndrome’, where there is congenital deficiency or absence
they run either with the lumbar arteries to drain into the lateral aortic of these muscles.
nodes, or with the intercostal and subcostal arteries to posterior media- Active contraction of the muscles provides an important role in the
stinal nodes. Lymphatics in the upper anterior abdominal wall run with maintenance of abdominal wall tone. The compression of the abdomi-


the superior epigastric vessels to parasternal nodes while those in the nal cavity required to increase intra-abdominal pressure is brought


1073
16
retPAHC
muscles
Muscular terminal branch
RA
Cutaneous artery
Intercostal artery
Inferior epigastric artery
PPF IOA SCF
PP TF EOA
Perforating cutaneous artery
Subcostal artery
TF IO SCF
PPF TA EO
Lumbar artery
RPF EO SCF
TLF LD
EO External oblique PP Parietal peritoneum SCF Subcutaneous fat
EOA External oblique aponeurosis PPF Preperitoneal fat TA Transversus abdominis
IO Internal oblique RA Rectus abdominis TF Transversalis fascia
IOA Internal oblique aponeurosis RPF Retroperitoneal fat TLF Thoracolumbar fascia
LD Latissimus dorsi
Fig. 61.4 The arrangement of the anterolateral abdominal wall vessels at the level of the mid-abdomen.
about mainly by contraction of the diaphragm. The bony pelvis, spine muscle, fusing with the fibres of the anterior lamina of the rectus sheath.
and lower thoracic cage provide rigidity to part of the abdominal wall. Occasionally, one or two incomplete intersections are present below the
During the generation of positive intra-abdominal pressure, the abdom- umbilicus. The intersections may represent the myosepta delineating
inal muscles act to hold the abdominal wall in a relatively fixed posi- the myotomes that form the muscle.
tion, rather than to generate pressure directly; because the majority of The medial border of each rectus abdominis abuts the linea alba. Its
the abdominal wall is muscular, the anterolateral abdominal wall lateral border may be visible on the surface of the anterior abdominal
muscles must be synchronously contracted to prevent displacement of wall as a gently curved groove, the linea semilunaris, which extends
the viscera and the resultant loss of pressure. The oblique muscles, from the tip of the ninth costal cartilage to the pubic tubercle. In a
acting through their anterior aponeuroses and the rectus sheath, provide muscular individual it is readily visible, even when the muscle is not
the majority of this tension, although transversus abdominis and rectus actively contracting, but in many normal and obese individuals it may
abdominis contribute. be completely obscured.
The anterolateral abdominal muscles contribute little to the move-