Peritoneum and peritoneal cavity

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CHAPTER 64 Peritoneum and peritoneal cavity

The peritoneum is the largest serous membrane in the body, and its arrangements are complex. In males it forms a closed sac, but in females it is open at the lateral ends of the uterine tubes. It consists of a single layer of flat mesothelial cells lying on a layer of loose connective tissue. The mesothelium usually forms a continuous surface, but in some areas may be fenestrated. Neighbouring cells are joined by junctional complexes, but probably permit the passage of macrophages. The submesothelial connective tissue may also contain macrophages, lymphocytes and adipocytes (in some regions). Mesothelial cells may transform into fibroblasts, which may play an important role in the formation of peritoneal adhesions after surgery or inflammation of the peritoneum.

The peritoneal cavity is a potential space between the parietal peritoneum, which lines the abdominal wall, and infoldings of visceral peritoneum, which suspend the abdominal viscera within the cavity. It contains a small amount of serous fluid, but is otherwise empty. The fluid lubricates the visceral peritoneum and allows the mobile viscera to glide freely on the abdominal wall and each other within the limits dictated by their attachments. It contains water, proteins, electrolytes and solutes derived from interstitial fluid in the adjacent tissues and from the plasma in the local blood vessels. It normally contains a few cells, including desquamated mesothelium, nomadic peritoneal macrophages, mast cells, fibroblasts, lymphocytes and other leukocytes. Some cells, particularly macrophages, migrate freely between the peritoneal cavity and the surrounding connective tissue. Lymphocytes provide both cellular and humoral immunological defence mechanisms within the peritoneal cavity. The intraperitoneal fluid is directed by gravity to dependent sites within the peritoneal cavity, and also flows in a cephalad direction as a consequence of the negative upper intra-abdominal pressures which are generated by respiration.

The peritoneal cavity never contains gas in normal circumstances, although the amount of fluid may be increased in inflammatory conditions of the viscera. In females blood or fluid may occasionally escape from the uterine tubes into the pelvic peritoneal cavity during menstruation.

Extraperitoneal connective tissue separates the parietal peritoneum from the muscular layers of the abdominal walls. The parietal peritoneum covering the anterior abdominal wall and pelvic walls is generally attached only loosely by this tissue, an arrangement which allows for considerable alteration in the size of the bladder and rectum. The extraperitoneal tissue on the inferior surface of the diaphragm and behind the linea alba is denser and more firmly adherent. The extraperitoneal tissue frequently contains large amounts of fat over the posterior abdominal wall, especially in obese males. The visceral peritoneum is firmly adherent to the underlying tissues and cannot be easily detached. Its connective tissue layer is often continuous with the fibrous matrix of the wall of the underlying viscera and rarely contains much loose connective or adipose tissue. The visceral peritoneum is often considered as part of the underlying viscus for clinical and pathological purposes such as the staging of carcinoma.

GENERAL ARRANGEMENT OF THE PERITONEUM

In utero, the alimentary tract develops as a single tube suspended in the coelomic cavity by ventral and dorsal mesenteries (see Ch. 73). Ultimately, the ventral mesentery is largely resorbed, although some parts persist in the upper abdomen and form structures such as the falciform ligament. The mesenteries of the intestines in the adult are the remnants of the dorsal mesentery. The migration and subsequent fixation of parts of the gastrointestinal tract produce the so-called ‘retroperitoneal’ segments of bowel (duodenum, ascending colon, descending colon, and rectum), and four separate intraperitoneal bowel loops suspended by mesenteries of variable lengths. These are all covered by visceral peritoneum which is continuous with the parietal peritoneum covering the posterior abdominal wall. The first intraperitoneal loop is formed by the intraperitoneal oesophagus, the stomach and first part of the duodenum. The second loop is made up of the duodenojejunal junction, jejunum, ileum and occasionally the caecum and proximal ascending colon. The third loop contains the transverse colon and the final loop contains the sigmoid colon and occasionally the distal descending colon.

Where the visceral peritoneum encloses or suspends organs within the peritoneal cavity, the peritoneum and related connective tissues are known as the peritoneal ligaments, omenta or mesenteries. All but the greater omentum are composed of two layers of visceral peritoneum separated by variable amounts of connective tissue. The greater omentum is folded back on itself and is therefore made up of four layers of closely applied visceral peritoneum, which are separated by variable amounts of adipose tissue. The mesenteries attach their respective viscera to the posterior abdominal wall: the attachment is referred to as the mesenteric root, and the peritoneum of the mesentery is continuous with that of the posterior abdominal wall in this area (Fig. 64.1).

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Fig. 64.1 The posterior abdominal wall, showing the lines of peritoneal reflection, after removal of the liver, spleen, stomach, jejunum, ileum, caecum, transverse colon and sigmoid colon. The various sessile (retroperitoneal) organs are seen shining through the posterior parietal peritoneum. Note: the ascending and descending colon, duodenum, kidneys, suprarenals, pancreas and inferior vena cava. Line W–W represents the plane of Fig. 64.2. Line X–X represents the plane of Fig. 64.3. Line Y–Y represents the plane of Fig. 64.4. Line A–A represents the plane of Fig. 64.5A. Line B–B represents the plane of Fig. 64.5B. Line C–C represents the plane of Fig. 64.5C.

Although they are described as intraperitoneal, strictly speaking the suspended organs do not lie within the peritoneal cavity because they are covered by visceral peritoneum. They are continuous with the extraperitoneal tissues, including the retroperitoneum, via subperitoneal tissue lying between the folds of visceral peritoneum. The loose areolar connective tissues of the extraperitoneal and subperitoneal tissues are sometimes conceptualized as ‘spaces’ because fluid or blood collects relatively easily within them. The subperitoneal tissues contain the neurovascular bundles and lymphatic channels which supply the suspended organs. In obese individuals, extensive adipose tissue within the mesenteries and omenta may obscure the neurovascular bundles. In contrast, in the very young, the elderly or the malnourished, the mesentery may contain very little adipose tissue and the neurovascular bundles are usually obvious.

PERITONEUM OF THE UPPER ABDOMEN

The abdominal oesophagus, stomach, liver and spleen all lie within a double fold of visceral peritoneum which runs from the posterior to the anterior abdominal wall. This fold has no recognized name, but has been referred to as the mesogastrium by Coakley & Hricak 1999 because it is derived from the fetal mesogastrium. It has a complex attachment to the wall of the abdominal cavity and gives rise to the falciform ligament, coronary ligaments, lesser omentum (gastrohepatic and hepatoduodenal ligaments), greater omentum (including gastrocolic ligament), gastrosplenic ligament, splenorenal ligament, and phrenicocolic ligament (Figs 64.2, 64.3, 64.4).

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Fig. 64.2 Sagittal section through the abdomen to the right of the epiploic foramen along one line of W–W in Fig. 64.1.

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Fig. 64.3 Section through the upper part of the abdominal cavity, along the line X–X in Fig. 64.1. The boundaries of the epiploic foramen are shown and a small recess of the lesser sac is displayed in front of the head of the pancreas. Note that the transverse colon and its mesocolon are adherent to the posterior two layers of the greater omentum.

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Fig. 64.4 Sagittal section through the abdomen, approximately in the median plane. Compare with Fig. 64.1. The section cuts the posterior abdominal wall along the line Y–Y in Fig. 64.1. The peritoneum is shown in blue except along its cut edges, which are left white.

The falciform ligament

The falciform ligament is a thin anteroposterior peritoneal fold which connects the liver to the posterior aspect of the anterior abdominal wall just to the right of the midline. It extends inferiorly to the level of the umbilicus, and is widest between the liver and umbilicus. The ligament narrows superiorly as the distance between the liver and anterior abdominal wall reduces and narrows to just a centimetre or so in height over the superior surface of the liver. Its two peritoneal layers divide to enclose the liver and are continuous with the visceral peritoneum that is adherent to the surface of the liver. Superiorly, they are reflected onto the inferior surface of the diaphragm and are continuous with the parietal peritoneum over the right dome. At the posterior limit, or apex, of the falciform ligament, the two layers are also reflected vertically left and right, and are continuous with the anterior layers of the left triangular ligament and the superior layer of the coronary ligament of the liver. The inferior aspect of the falciform ligament forms a free border where the two peritoneal layers become continuous with each other as they fold over to enclose the ligamentum teres. Because the peritoneum of the falciform ligament is continuous with that covering the posterior abdominal wall and the periumbilical anterior abdominal wall, blood arising from retroperitoneal haemorrhage (commonly acute haemorrhagic pancreatitis) may track between the folds of peritoneum and appear as haemorrhagic discolouration around the umbilicus (Cullen’s sign). Inflammatory change from the pancreas may spread via the gastrohepatic ligament (lesser omentum) and then via the falciform ligament to the umbilicus.

The peritoneal connections of the liver

The liver is almost completely covered in visceral peritoneum, and only the ‘bare area’ is in direct contact with the right dome of the diaphragm. Peritoneal folds, the ligaments of the liver, run from the liver to the surrounding viscera and to the abdominal wall and diaphragm (Fig. 64.5); they are described in detail in Chapter 68.

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Fig. 64.5 Transverse sections through the abdomen. A, At the level of the line A–A in Fig. 64.1. The line passes through the bare area of the liver at the superior end of the lesser omentum. The parts of the left subphrenic space are clearly seen although they are continuous with each other. B, At the level of line B–B in Fig. 64.1, viewed from below. The peritoneal cavity is shown by a blue ‘wash’; the peritoneum and its cut edges in pale blue. C, Transverse section through the abdomen at the level of the line C–C in Fig. 64.1, viewed from below. Colours as in Fig. 64.1.

The coronary ligament is formed by the reflection of the peritoneum from the diaphragm onto the posterior surfaces of the right lobe of the liver. Between the two layers of this ligament, a large area of liver, the bare area, is devoid of peritoneal covering. At this point the liver is attached to the diaphragm by areolar tissue and is in continuity inferiorly with the uppermost part of the anterior pararenal space. The layers of the coronary ligament are continuous on the right with the right triangular ligament.

The upper layer of the coronary ligament is continuous superiorly with the peritoneum over the inferior surface of the diaphragm and inferiorly with the peritoneum over the right and superior surfaces of the liver. At the lower margin of the bare area the lower layer of the coronary ligament becomes continuous inferiorly with the peritoneum of the posterior abdominal wall over the right suprarenal gland and upper pole of the right kidney, and superiorly with the peritoneum over the inferior surface of the liver.

The left triangular ligament is a double layer of peritoneum which extends over the superior border of the left lobe of the liver to a variable length. Medially, its anterior leaf is continuous with the left layer of the falciform ligament. The posterior layer is continuous with the left layer of the lesser omentum. The left triangular ligament lies in front of the abdominal part of the oesophagus, the upper end of the lesser omentum and part of the fundus of the stomach. Intraoperative division of the left triangular ligament permits mobilization of the left lobe of the liver in order to expose the abdominal oesophagus and crura of the diaphragm.

The right triangular ligament is a short V-shaped fold formed by the approximation of the two layers of the coronary ligament at its right lateral end, and is continuous with the peritoneum of the right posterolateral abdominal wall. The coronary ligament is reflected inferiorly and is directly continuous with the peritoneum over the upper pole of the right kidney. This fold is sometimes referred to as the hepatorenal ligament. The recess formed between the peritoneum of the inferior surface of the liver, the hepatorenal ligament and the peritoneum over the right kidney is known as the hepatorenal pouch (of Morison). In the supine position this is the most dependent part of the peritoneal cavity in the upper abdomen, and is a common site of pathological fluid accumulation.

The peritoneum is reflected inferolaterally from the posterior layer of the left triangular ligament onto the posterior abdominal wall above the oesophageal opening of the diaphragm. It lines the inferior surface of the left dome of the diaphragm and continues backwards onto the posterior abdominal wall. Inferiorly, it is reflected behind the spleen onto the most lateral part of the mesentery of the transverse colon and the splenic flexure. It continues down lateral to the descending colon into the pelvis, and forms the left paracolic ‘gutter’. Medially, the peritoneum covering the left upper posterior abdominal wall is reflected anteriorly to form the left layer of the upper end of the lesser omentum, the peritoneum over the left aspect of the abdominal oesophagus and the left layer of the splenorenal ligament.

From the inferior layer of the coronary ligament the peritoneum descends over the anterior surface of the right kidney to the front of the first part of the duodenum and hepatic flexure of the colon. Medially it passes in front of a short segment of the inferior vena cava between the duodenum and liver, forming as it does so the posterior wall of the epiploic foramen. This narrow strip broadens out as the peritoneum continues across the midline onto the posterior wall of the lesser sac.

The peritoneum lines the posterior abdominal wall over the diaphragmatic crura, the upper abdominal aorta, the coeliac axis, nodes and plexus and the upper border of the pancreas. Inferiorly, below the liver, it continues down on the posterior abdominal wall to the right of the ascending colon, forming the right paracolic ‘gutter’ between the anterolateral abdominal wall and colon.

The lesser omentum

The lesser omentum is formed of two layers of peritoneum separated by a variable amount of connective tissue and is derived from the ventral mesogastrium. It runs from the inferior visceral surface of the liver to the abdominal oesophagus, stomach, pylorus and first part of the duodenum. Superiorly, its attachment to the inferior surface of the liver forms an L-shape. The vertical component of the L is formed by the fissure for the ligamentum venosum. Inferiorly, the attachment turns and runs horizontally to complete the L in the portal fissure. The vertical and horizontal components of the lesser omentum run between the liver and the stomach and duodenum and are known as the gastrohepatic and hepatoduodenal ligaments, respectively. At the lesser curvature of the stomach, the layers of the lesser omentum split to enclose the stomach and are continuous with the visceral peritoneum covering the anterior and posterior surfaces of the stomach. The anterior layer of the lesser omentum descends from the fissure for the ligamentum venosum onto the anterior surface of the abdominal oesophagus, stomach and duodenum. The posterior layer descends from the posterior part of the fissure for the ligamentum venosum and runs onto the posterior surface of the stomach and pylorus. The lesser omentum forms the anterior surface of the lesser sac. The gastrohepatic ligament contains the right and left gastric vessels, branches of the vagus nerves, and gastrohepatic lymph nodes between its two layers near their attachment to the stomach. The right lateral border of the lesser omentum is thickened and extends from the junction between the first and second parts of the duodenum to the porta hepatis. This border is free and forms the anterior wall of the epiploic foramen. It contains the portal vein, common bile duct, hepatic artery, portocaval lymph nodes and lymphatics and the hepatic plexus of nerves ensheathed in a perivascular fibrous capsule. Occasionally the free margin extends to the right of the epiploic foramen, runs to the gallbladder and is referred to as the cystoduodenal ligament.

The left border of the lesser omentum is short and runs over the inferior surface of the diaphragm between the liver and medial aspect of the abdominal oesophagus. The lesser omentum is thinner on the left and may be fenestrated or incomplete: the variations in thickness are dependent upon the amount of connective tissue, especially fat.

The greater omentum

The greater omentum is the largest peritoneal fold and hangs inferiorly from the greater curvature of the stomach. It is a double sheet: each sheet consists of two layers of peritoneum separated by a scant amount of connective tissue. The two sheets are folded back on themselves and are firmly adherent to each other. The anterior sheet descends from the greater curvature of the stomach and first part of the duodenum. The most anterior layer is continuous with the visceral peritoneum over the anterior surface of the stomach and duodenum and the posterior layer is continuous with the peritoneum over the posterior wall of the stomach and pylorus. The anterior sheet descends a variable distance into the peritoneal cavity and then turns sharply on itself to ascend as the posterior sheet. The posterior sheet passes anterior to the transverse colon and transverse mesocolon. It is attached to the posterior abdominal wall above the origin of the small intestinal mesentery and anterior to the head and body of the pancreas. The anterior layer of the posterior sheet is continuous with the peritoneum of the posterior wall of the lesser sac. The posterior layer is reflected sharply inferiorly and is continuous with the anterior layer of the transverse mesocolon. The posterior sheet is adherent to the transverse mesocolon at its root and is often known as the gastrocolic ligament, which is the supracolic part of the greater omentum. In early fetal life the greater omentum and transverse mesocolon are separate structures, and this arrangement sometimes persists. During surgical mobilization of the transverse colon, the plane between the transverse mesocolon and greater omentum can be entered opposite the taenia omentalis, and the greater omentum can be separated entirely from the transverse colon and mesocolon if required. Access into the lesser sac can be obtained via this approach if the upper part of the posterior sheet of the greater omentum is then divided. This gives a relatively bloodless plane of entry for surgical access to the posterior wall of the stomach and to the anterior surface of the pancreas. The greater omentum is continuous with the gastrosplenic ligament on the left, and on the right it extends to the start of the duodenum. A fold of peritoneum, the hepatocolic ligament, may run from either the inferior surface of the right lobe of the liver or the first part of the duodenum to the right side of the greater omentum or hepatic flexure of the colon.

The right border of the greater omentum is occasionally adherent to the anterior surface of the ascending colon down as far as the caecum: its peritoneal layers are not continuous with the peritoneum over this part of the colon. A thin sheet of peritoneum referred to as Jackson’s membrane may run from the front of the ascending colon and caecum to the posterolateral abdominal wall and may merge with the greater omentum. It often contains several small blood vessels. Occasionally, a band passes from the right side of the ascending colon to the lateral abdominal wall near the level of the iliac crest. It has been called the ‘sustentaculum hepatis’ but plays no role in the support of the liver. Other folds between the ascending colon and posterolateral abdominal wall may divide the right lateral paracolic gutter into several small recesses. Less commonly the greater omentum is adherent to the anterior surface of the left colon; very occasionally it extends to the level of the sigmoid colon.

When the undisturbed abdomen is opened, the greater omentum is frequently wrapped around the upper abdominal organs. Only rarely is it evenly dependent anterior to the coils of the small intestine, although this is the disposition which is frequently illustrated. It is usually thin and cribriform, but it always contains some adipose tissue and is a common site for storage of fat in obese individuals, particularly males.

Between the two layers of the anterior fold of the greater omentum, close to the greater curvature of the stomach, the right and left gastroepiploic vessels form a wide anastomotic arc. Numerous vessels are given off from the arc and extend the full length of the omentum. This supply appears to exceed the metabolic requirements of the omentum, and perhaps reflect the role the greater omentum may play in peritoneal disease processes. The greater omentum is highly mobile and frequently becomes adherent to inflamed viscera within the abdominal cavity. This action may help to limit the spread of infection and the omentum may provide a source of well-vascularized tissue to take part in the early reparative process. It contains numerous fixed macrophages, which are easily mobilized when activated and may accumulate into dense, oval or round visible ‘milky-spots’.

The peritoneal connections of the spleen

The peritoneal connections of the spleen suspend the spleen in the left upper quadrant of the abdomen; they include the gastrosplenic, splenorenal and phrenicocolic ligaments. The gastrosplenic ligament runs between the greater curvature of the stomach and the hilum of the spleen and is in continuity with the left side of the greater omentum. The layers of the gastrosplenic ligament separate to enclose the spleen and then rejoin to form the splenorenal ligament and phrenicocolic ligaments. The splenorenal ligament extends from the spleen to the posterior abdominal wall and the phrenicocolic ligament extends to the anterolateral abdominal wall.

The splenorenal ligament is formed from two layers of peritoneum. The anterior layer is continuous medially with the peritoneum of the posterior wall of the lesser sac over the left kidney and runs up to the splenic hilum where it is continuous with the posterior layer of the gastrosplenic ligament. The posterior layer of the splenorenal ligament is continuous laterally with the peritoneum over the inferior surface of the diaphragm and runs onto the splenic surface over the renal impression. The splenic vessels lie between the layers of the splenorenal ligament: the tail of the pancreas is usually present in its lower portion. The gastrosplenic ligament also has two layers. The posterior layer is continuous with the peritoneum of the splenic hilum and the peritoneum over the posterior surface of the stomach. The anterior layer is formed from the peritoneum reflected off the gastric impression of the spleen and is continuous with the peritoneum over the anterior surface of the stomach. The short gastric and left gastroepiploic branches of the splenic artery, with their corresponding veins, pass between the layers of the gastrosplenic ligament. The phrenicocolic ligament extends from the splenic flexure of the colon to the diaphragm at the level of the eleventh rib. It extends inferiorly and laterally and is continuous with the peritoneum of the lateral end of the transverse mesocolon at the lateral margin of the pancreatic tail, and the splenorenal ligament at the hilum of the spleen.

A fan-shaped presplenic fold frequently extends from the anterior aspect of the gastrosplenic ligament near the greater curvature of the stomach below the inferolateral pole of the spleen and blends with the phrenicocolic ligament.

If the peritoneal attachments of the spleen are not recognized during surgery, the splenic capsule is at risk of injury and there may be subsequent serious bleeding. Downward traction on the phrenicocolic ligament during handling of the descending colon, especially during mobilization of the splenic flexure, may cause rupture of the splenic capsule. This is less likely if traction on the phrenicocolic ligament is made laterally or medially. The superior border and anterior diaphragmatic surface of the splenic capsule are often adherent to the peritoneum of the greater omentum. Medial traction on the omentum during surgery may cause splenic capsular injury: such injury is less likely, if any limited traction required is applied inferiorly.

PERITONEUM OF THE LOWER ABDOMEN

The posterior surface of the lower anterior abdominal wall is lined by parietal peritoneum, which extends from the linea alba centrally to the lateral border of quadratus lumborum. Here it is continuous with the peritoneum of the lateral paracolic gutter and is reflected over the sides and front of the ascending colon on the right and the descending colon on the left. Occasionally the ascending and descending colon are suspended by a short mesentery from the posterior abdominal wall. Between the ascending and descending colon, the peritoneum lines the posterior abdominal wall other than the oblique area, where it is reflected anteriorly to form the right and left layers of the small intestinal mesentery. Over the posterior abdominal wall it covers the left and right psoas major, inferior vena cava, duodenum, vertebral column and right and left ureters. At the upper extent of the posterior abdominal wall the peritoneum is reflected anteriorly and is continuous with the peritoneum of the posterior layer of the transverse mesocolon.

Transverse mesocolon

The mesentery of the transverse colon is a broad fold of visceral peritoneum reflected anteriorly from the posterior abdominal wall and suspends the transverse colon in the peritoneal cavity. The root of the transverse mesocolon lies along an oblique line passing from the anterior aspect of the second part of the duodenum, over the head and neck of the pancreas, above the duodenojejunal junction and over the upper pole of the left kidney to the splenic flexure (Fig. 64.1). It varies considerably in length but is shortest at either end. It contains the middle colic vessels and their branches together with branches of the superior mesenteric plexus, lymphatics and regional lymph nodes. Its two layers pass to the posterior surface of the transverse colon, where they separate to cover the colon. The upper layer of peritoneum is reflected from the posterior abdominal wall immediately anteriorly and inferiorly and becomes continuous with the posterior layer of the greater omentum to which it is adherent. The lower layer of peritoneum of the transverse mesocolon is continuous with the peritoneum of the posterior abdominal wall. Lateral extensions of the transverse mesocolon produce two shelf-like folds on the right and left sides of the abdominal cavity. On the right the duodenocolic ligament extends from the transverse mesocolon at the hepatic flexure to the second part of the duodenum. On the left the phrenicocolic ligament extends from the transverse mesocolon at the splenic flexure to the diaphragm at the level of the eleventh rib. The root of the transverse mesocolon is closely related to the upper limit of the root of the mesentery of the small intestine near the uncinate process of the pancreas.

Mesentery of the small intestine

The mesentery of the small intestine is arranged as a complex fan formed from two layers of peritoneum (anterosuperior and posteroinferior) separated by connective tissue and vessels. The root of the mesentery lies along a line running diagonally from the duodenojejunal flexure on the left side of the second lumbar vertebral body to the right sacroiliac joint (Fig. 64.1). The root crosses over the third part of the duodenum, aorta, inferior vena cava, right ureter and right psoas major. The average length of the root of the mesentery is 15 cm in adults; while along its intestinal attachment is the same length as the small intestine (approximately 5 m), and consequently the mesentery is usually thrown into multiple folds along its intestinal border. The average depth of the mesentery from the root to the intestinal border is 20 cm, but this varies along the length of the small intestine: it is shortest at the jejunum and terminal ileum and longest in the region of the mid ileum. Its two peritoneal layers contain the jejunum, ileum, jejunal and ileal branches of the superior mesenteric vessels, branches of the superior mesenteric plexus, lacteals and regional lymph nodes. Because of the length and mobility of the mesentery, identification of the proximal and distal ends of a loop of small intestine may be difficult through small surgical incisions. Tracing the continuity of the right peritoneal layer of the mesentery onto the posterior abdominal wall above the root towards the ascending colon, and the continuity of the left layer towards the descending and sigmoid colon, may be useful in helping to orientate an individual loop of ileum. The mesentery of the small intestine is sometimes joined to the transverse mesocolon at the duodenojejunal junction by a peritoneal band. Occasionally the fourth part of the duodenum possesses a very short mesentery which is continuous with the upper end of the root of the small bowel mesentery. Pronounced bands of peritoneum may extend to the posterior abdominal wall at the terminal ileum. The root of the mesentery of the small intestine is continuous with the peritoneum surrounding the appendix and caecum in the right iliac fossa.

Mesoappendix

The mesentery of the appendix is a triangular fold of peritoneum around the vermiform appendix, attached to the posterior surface of the lower end of the mesentery of the small intestine close to the ileocaecal junction. It usually reaches the tip of the appendix but sometimes fails to reach the distal third, in which case a vestigial low peritoneal ridge containing fat is present over the distal third. It encloses the blood vessels, nerves and lymph vessels of the vermiform appendix, and usually contains a lymph node.

Sigmoid mesocolon

The sigmoid mesocolon shows individual variation in length and depth. The root of the sigmoid colon forms a shallow inverted V with an apex near the division of the left common iliac artery but may vary from a very short straight line at the pelvic brim to a long curved attachment. The upper, left end of the attachment runs medially over the left psoas major. The lower, right end passes into the pelvis towards the midline at the level of the third sacral vertebra. The root extends for a variable distance over the brim of the pelvis and the lower posterior abdominal wall. The anteromedial peritoneal layer of the mesentery of the sigmoid colon is continuous with the peritoneum of the lower left posterior abdominal wall and its posterolateral layer is continuous with the peritoneum of the pelvis and lateral abdominal wall. The proximal and distal ends of the sigmoid colon are occasionally joined together by a fibrous band which is usually associated with a narrow based sigmoid mesentery and may predispose the sigmoid colon to volvulus. Pronounced bands of peritoneum may also be found running from the proximal sigmoid colon to the posterior abdominal wall. The sigmoid and superior rectal vessels run between its layers and the left ureter descends into the pelvis behind its apex.

PERITONEUM OF THE LOWER ANTERIOR ABDOMINAL WALL

The peritoneum of the lower anterior abdominal wall is raised into five ridges which diverge as they descend from the umbilicus. These are the median and right and left lateral and medial umbilical folds (Fig. 64.6). The median umbilical fold extends from the umbilicus to the apex of the bladder and contains the urachus or its remnant (Ch. 78). The obliterated umbilical artery lies under the medial umbilical fold which ascends from the pelvis to the umbilicus. The supravesical fossa lies between the medial and median umbilical folds on either side of the midline. The lateral umbilical fold covers the inferior epigastric artery and vein below their entry into the rectus sheath, and is separated from the medial umbilical fold by the medial inguinal fossa. The lateral inguinal fossa lies lateral to the lateral umbilical fold, and covers the deep inguinal ring. The femoral fossa lies inferomedial to the lateral inguinal fossa, from which it is separated by the medial end of the inguinal ligament. It overlies the femoral ring (see Ch. 61).

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Fig. 64.6 The infra-umbilical part of the anterior abdominal wall of a male subject: posterior surface, with the peritoneum in situ. Note the pelvic bones flanking the wide greater pelvis (middle) and narrower lesser pelvis (below) containing the bladder.

PERITONEUM OF THE PELVIS

The parietal peritoneum of the posterior surface of the anterior abdominal wall and that lining the posterior abdominal wall continue into the pelvis as the pelvic peritoneum. The pelvic peritoneum then follows the surfaces of the true pelvic viscera and pelvic side walls although there are important differences between the sexes.

Peritoneum of the male pelvis

In males, the peritoneum of the left lower abdominal wall is reflected from the junction of the sigmoid colon and anterolateral surface of the rectum to line the brim and upper inner surface of the true pelvis (Fig. 64.7). The peritoneum passes down into the true pelvis, lying over the anterior surface of the rectum, which then becomes an extraperitoneal organ. Laterally, the peritoneum is reflected to the pelvic side walls to form the right and left pararectal fossae: these vary in size according to the degree of distension of the rectum. The peritoneum is reflected anteriorly from the anterior surface of the rectum over the upper poles of the seminal vesicles and onto the posterior surface of the bladder, producing the rectovesical pouch. Anteriorly the rectovesical pouch is limited laterally by peritoneal folds, the sacrogenital folds, which extend from the sides of the bladder posteriorly to the anterior aspect of the sacrum. The peritoneum covers the superior surface of the bladder, and forms a paravesical fossa on each side limited laterally by a ridge of peritoneum which contains the ductus deferens. The size of the paravesical fossae depends on the volume of urine in the bladder. When the bladder is empty, a variable transverse vesical fold divides each fossa into two. The anterior ends of the sacrogenital folds may sometimes be joined by a ridge separating a middle fossa from the main rectovesical pouch. Between the paravesical and pararectal fossae the ureters and internal iliac vessels may cause slight elevations in the peritoneum. From the apex of the bladder the peritoneum extends superiorly along the posterior surface of the lower anterior abdominal wall to the umbilicus. When the bladder distends, the peritoneum is lifted from the lower anterior abdominal wall so that part of the anterior surface of the bladder is in direct contact with the posterior surface of the lower median area of the anterior abdominal wall. This relationship means that a well-distended bladder can be entered by direct puncture through the lower anterior abdominal wall without entering the peritoneal cavity (suprapubic puncture).

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Fig. 64.7 The peritoneum of the male pelvis: anterosuperior view. The median umbilical fold contains both the unpaired median and the paired medial umbilical ligaments in the plane of section in this subject.

Peritoneum of the female pelvis

In females the peritoneum covers the upper rectum as it does in the male, but it descends further over the anterior surface of the rectum. The lateral limit of the pararectal and paravesical fossae is the peritoneum covering the round ligament of the uterus. The rectovesical pouch is occupied by the uterus and vagina. The peritoneum from the rectum is thus reflected anteriorly onto the posterior surface of the posterior fornix of the vagina and the uterus, producing the recto-uterine pouch (of Douglas). The peritoneum covers the fundus of the uterus to its anterior (vesical) surface as far as the junction of the body and cervix, from which it is reflected forwards to the upper surface of the bladder, forming a shallow vesico-uterine pouch. Peritoneum is reflected from the bladder to the posterior surface of the anterior abdominal wall as it is in males. Marginal recto-uterine folds correspond to the sacrogenital folds in males and pass back to the sacrum from the sides of the cervix, lateral to the rectum. Peritoneum is reflected from the anterior and posterior uterine surfaces to the lateral pelvic walls as the broad ligament of the uterus (see Fig. 77.18). This consists of anteroinferior and posterosuperior layers which are continuous at the upper border of the ligament. The broad ligament extends from the sides of the uterus to the lateral pelvic walls, and contains the uterine tubes in its free superior margins and the ovaries attached to its posterior layer. Below, it is continuous with the lateral pelvic parietal peritoneum. Between the ridges formed by the obliterated umbilical arteries and the ureter, the peritoneum forms a shallow depression on the lateral pelvic wall, the ovarian fossa, which lies behind the lateral attachment of the broad ligament. The ovary usually rests in the fossa in nulliparous females.

VASCULAR SUPPLY AND LYMPHATIC DRAINAGE

Parietal and visceral peritoneum develop from the somatopleural and splanchnopleural layers respectively of lateral plate mesoderm (see Ch. 73). Parietal peritoneum is therefore supplied by somatic blood vessels of the abdominal and pelvic walls and its lymphatics join those in the body wall and drain to parietal lymph nodes. Visceral peritoneum is best considered as an integral part of the viscera which it overlies; it derives its blood supply from the viscera, and its lymphatics join the visceral vessels to drain to the regional lymph nodes.

INNERVATION

The parietal peritoneum is innervated by branches from somatic efferent and afferent nerves that also supply the muscles and skin respectively of the overlying body wall. The visceral peritoneum is innervated by branches of visceral afferent nerves which travel with the autonomic supply to the underlying viscera. The different sensations arising from pathologies which affect either the parietal or visceral peritoneum reflect these differences in patterns of innervation. Well-localized pain is elicited by mechanical, thermal or chemical stimulation of the nocioceptors of the parietal peritoneum. The sensation is usually confined to one or two dermatomes for each area of peritoneum stimulated and is both lateralized and well localized. Somatic nerves that innervate the parietal peritoneum also supply the corresponding segmental areas of skin and muscles; when the parietal peritoneum is irritated, muscles tend to contract reflexly, causing localized hypercontractility (guarding) or even rigidity of the abdominal wall. The parietal diaphragmatic peritoneum is supplied with afferent fibres from the phrenic nerves (centrally) and by the lower six intercostal nerves and subcostal nerves (peripherally): peripheral irritation of the diaphragm may therefore result in pain, tenderness and muscular rigidity in the distribution of the lower thoracic spinal nerves, while central irritation may result in pain in the cutaneous distribution of the third to fifth cervical spinal nerves, i.e. the shoulder region.

The visceral peritoneum and viscera are not affected by these stimuli because the visceral afferent innervation provides a much more limited sensation of discomfort. When stimulated, the sensation of pain is of a less severe nature and is referred to the area of abdominal wall according to the region of the intestinal tract affected. Discomfort from structures derived from the foregut is felt in the region of the epigastrium, from midgut structures in the region of the umbilicus, and from hindgut structures in the suprapubic region: none of these sensations shows significant lateralization. However, stretch of the visceral peritoneum is a potent cause of certain sensations and responses. Various neural elements in the visceral walls, mesenteries and overlying peritoneum mediate poorly localized sensations of discomfort when stimulated by stretch, and may also elicit profound reflex autonomic reactions involving vasomotor and cardiac changes. This is of considerable clinical relevance. The effects of division of the parietal peritoneum may be rendered painless by local or regional local anaesthesia. In marked contrast, the direct central connections of the visceral afferents, particularly via the vagus, mean that stretching the visceral peritoneum may have profound effects, and may produce acute haemodynamic instability despite high spinal anaesthesia. Ischaemia of the underlying viscera causes poorly localized abdominal pain, probably due to the spasms of visceral smooth muscle.

GENERAL ARRANGEMENT OF THE PERITONEAL CAVITY

The peritoneal cavity is a single continuous space between the parietal peritoneum lining the abdominal wall and the visceral peritoneum enveloping the abdominal organs. It consists of a main region, termed the greater sac, which is equivalent to the main abdominal cavity surrounding the majority of the abdominal and pelvic viscera. The lesser sac, or omental bursa, is a small diverticulum lined with peritoneum, which is situated behind the stomach and lesser omentum and in front of the pancreas and retroperitoneum. These two areas communicate via the epiploic foramen.

For clinical purposes the peritoneal cavity can be divided into several spaces because pathological processes are often contained within these spaces and their anatomy may influence diagnosis and treatment. It is useful to divide the peritoneal cavity into two main compartments, supramesocolic and inframesocolic, which are partially separated by the transverse colon and its mesentery (the latter connects the transverse colon to the posterior abdominal wall). The pelvic peritoneal spaces are described above.

SUPRAMESOCOLIC COMPARTMENT

The supramesocolic space lies above the transverse mesocolon between the diaphragm and the transverse colon. It can be arbitrarily divided into right and left supramesocolic spaces. These regions can be further subdivided into a number of subspaces, which are normally in communication, but are frequently subdivided by inflammatory adhesions in disease. The right supramesocolic space can be divided into three subspaces; the right subphrenic space, the right subhepatic space, and the lesser sac. The left supramesocolic space can be divided into two subspaces; the left subphrenic space and the left perihepatic space.

Right subphrenic space

The right subphrenic space lies between the diaphragm and the anterior, superior and right lateral surfaces of the right lobe of the liver. It is bounded on the left side by the falciform ligament and behind by the upper layer of the coronary ligament. It is a relatively common site for collections of fluid after right sided abdominal inflammation.

Right subhepatic space (hepatorenal recess)

The right subhepatic space lies between the right lobe of the liver and the right kidney. It is bounded superiorly by the inferior layer of the coronary ligament, laterally by the right lateral abdominal wall, posteriorly by the anterior surface of the upper pole of the right kidney and medially by the second part of the duodenum, hepatic flexure, transverse mesocolon and part of the head of the pancreas. In the supine position the posterior right subhepatic space is more dependent than the right paracolic gutter: postoperative infected fluid collections are common in this location.

Lesser sac (omental bursa)

The lesser sac is a cavity lined with peritoneum and connected to the larger general peritoneal cavity (greater sac) by the epiploic foramen. It is considered part of the right supramesocolic space because embryologically the liver grows into the right peritoneal space and stretches the dorsal mesentery to form the lesser sac behind the stomach. The sac varies in size according to the size of the viscera making up its walls. It has posterior and anterior walls as well as superior, inferior, right and left borders.

The anterior wall is made up of the posterior peritoneal layer of the lesser omentum, the peritoneum over the posterior wall of the stomach and first part of the duodenum, and the uppermost part of the anterior layer of the greater omentum. At its right border, the anterior wall is mostly formed by the lesser omentum but moving towards the left, the lesser omentum becomes progressively shorter and more of the anterior wall is formed by the posterior aspect of the stomach and greater omentum.

The posterior wall is formed mainly by the peritoneum covering the posterior abdominal wall in this area. In the lower part, the posterior wall is made up of the anterior layer of the posterior sheet of the greater omentum as it lies on the transverse mesocolon. The posterior wall covers, from below upwards, a small part of the head and the whole neck and body of the pancreas, the medial part of the anterior aspect of the left kidney, most of the left suprarenal gland, the commencement of the abdominal aorta and coeliac artery and part of the diaphragm. The inferior phrenic, splenic, left gastric and hepatic arteries lie partly behind the bursa. Many of these structures form the ‘bed’ of the stomach and are separated from it only by the linings of the lesser sac.

The superior border of the lesser sac is narrow and lies between the right side of the oesophagus and the upper end of the fissure for the ligamentum venosum. Here peritoneum of the posterior wall of the lesser sac is reflected anteriorly from the diaphragm to join the posterior layer of the lesser omentum.

The inferior border of the lesser sac runs along the line of the fusion of the layers of the greater omentum. This runs from the gastrosplenic ligament to the peritoneal fold behind the first part of the duodenum. In cases where the layers are not completely adherent to each other, the lesser sac may extend as far as the bottom of the two sheets of the greater omentum. In adults, even in these circumstances of separation of the layers, the lowest extent of the inferior border is rarely below the level of the transverse colon.

The right border of the lesser sac is formed by the reflection of the peritoneum from the pancreatic neck and head onto the inferior aspect of the first part of the duodenum. The line of this reflection ascends to the left, along the medial side of the gastroduodenal artery. Near the upper duodenal margin the right border joins the floor of the epiploic foramen round the hepatic artery proper. The epiploic foramen thus forms a break in the right border. Above the epiploic foramen the right border is formed by the reflection of peritoneum from the diaphragm to the right margin of the caudate lobe of the liver and along the left side of the inferior vena cava, enclosing the hepatic recess.

The left border of the lesser sac runs from the left end of the root of the transverse mesocolon and is mostly formed by the inner layer of peritoneum of the splenorenal and gastrosplenic ligaments. The part of the lesser sac lying between the splenorenal and gastrosplenic ligaments is referred to as the splenic recess. Above the level of the spleen, the two ligaments are merged as the short gastrophrenic ligament, which passes forwards from the diaphragm to the posterior aspect of the fundus of the stomach and forms part of the upper left border of the lesser sac. The two layers of the gastrophrenic ligament diverge near the abdominal oesophagus, leaving part of the posterior gastric surface devoid of peritoneum. The left gastric artery runs forwards here into the lesser omentum.

The lesser sac is narrowed by two crescentic peritoneal folds produced by the hepatic and left gastric arteries. The left gastropancreatic fold overlies the left gastric artery as it runs from the posterior abdominal wall to the lesser curvature of the stomach. The right gastropancreatic fold overlies the hepatic artery as it runs from the posterior abdominal wall to the lesser omentum. The folds vary in size. When prominent, they divide the lesser sac into a smaller superior and a larger inferior recess. The superior recess lies posterior to the lesser omentum and liver, and encloses the caudate lobe of the liver, which is covered by peritoneum on both its anterior and posterior surfaces. It extends superiorly into the fissure for the ligamentum venosum and lies adjacent to the right crus of the diaphragm posteriorly. The inferior recess of the lesser sac lies between the stomach and pancreas and is contained in the double sheet of the greater omentum.

Epiploic foramen (of Winslow)

The epiploic foramen (foramen of Winslow, aditus to the lesser sac), is a short, vertical slit, usually 3 cm in height in adults, in the upper part of the right border of the lesser sac. It leads into the greater sac. The hepatoduodenal ligament, which is formed by the thickened right edge of the lesser omentum extending from the flexure between the first and second parts of the duodenum, forms the anterior margin of the foramen. The anterior border contains the common bile duct (on the right), portal vein (posteriorly) and hepatic artery (on the left) between its two layers. Superiorly the peritoneum of the posterior layer of the hepatoduodenal ligament runs over the caudate lobe of the liver which forms the roof of the epiploic foramen. This layer of peritoneum is then reflected onto the inferior vena cava which forms the posterior margin of the epiploic foramen. At the upper border of the first part of the duodenum the peritoneum runs forwards from the inferior vena cava, above the head of the pancreas, and is continuous with the posterior layer of the lesser omentum, forming the floor of the epiploic foramen. A narrow passage, the vestibule of the lesser sac, may be found to the left of the foramen between the caudate process and the first part of the duodenum. To the right, the rim of the foramen is continuous with the peritoneum of the greater sac. The roof is continuous with the peritoneum on the inferior surface of the right hepatic lobe. The anterior and posterior walls of the foramen are normally apposed.

Left subphrenic space

The left subphrenic space lies between the diaphragm, the anterior and superior surfaces of the left lobe of the liver, the anterosuperior surface of the stomach and the diaphragmatic surface of the spleen. It is bounded to the right by the falciform ligament and behind by the anterior layer of the left triangular ligament. It is much enlarged in the absence of the spleen and is a common site for fluid collection particularly after splenectomy. The left subphrenic space is substantially larger than the right and is sometimes described as being divided into anterior and posterior parts, although no obvious demarcation exists in the absence of disease. The left posterior subphrenic space is small and lies between the fundus of the stomach and the diaphragm above the origin of the splenorenal ligament. The left anterior subphrenic space is large and lies between the superior and anterolateral surfaces of the spleen and the left dome of the diaphragm. Inferiorly and medially, this space is bounded by the splenorenal, gastrosplenic, and phrenicocolic ligaments which produces a partial barrier to the left paracolic gutter. This may explain why left subphrenic collections are less frequent than right subphrenic collections following lower abdominal and pelvic surgery, but the left subphrenic space is the commonest site of fluid collection after upper abdominal, particularly splenic, surgery.

Left perihepatic space

The left perihepatic space is sometimes subdivided into anterior and posterior spaces. The posterior perihepatic space is also known as the left subhepatic space or gastrohepatic recess. The left anterior perihepatic space lies between the anterosuperior surface of the left lobe of the liver and diaphragm. The left posterior perihepatic space lies inferior to the left lobe of the liver, and extends into the fissure for the ligamentum venosum on the right, anterior to the main portal vein. Posteriorly, the lesser omentum separates this space from the superior recess of the lesser sac. On the left, the space is bounded by the lesser curvature of the stomach.

INFRAMESOCOLIC COMPARTMENT

The inframesocolic compartment lies below the transverse mesocolon and transverse colon are far as the true pelvis. It is divided in two unequal spaces by the root of the mesentery of the small intestine. It contains the right and left paracolic gutters lateral to the ascending and descending colon. As a consequence of the mobility of the transverse mesocolon and mesentery of the small intestine, disease processes are rarely well contained within these spaces, and fluid within the infracolic space tends to descend into the pelvis or the paracolic gutters.

Right infracolic space

The right infracolic space is a triangular space. It is smaller than its counterpart on the left, and lies posterior and inferior to the transverse colon and mesocolon and to the right of the small intestinal mesentery. The space is narrowest inferiorly because the attachment of the root of the mesentery of the small intestine lies well to the right of the midline. The vermiform appendix often lies in the lower part of the right infracolic space.

Left infracolic space

The left infracolic space is larger than its counterpart on the right and is in free communication with the pelvis to the right of the midline. It lies posterior and inferior to the transverse colon and mesocolon and to the left of the mesentery of the small intestine. The sigmoid colon and its mesentery may partially restrict the flow of fluid or blood into the pelvis to the left of the midline.

Paracolic gutters

The right and left paracolic gutters are peritoneal recesses on the posterior abdominal wall lying alongside the ascending and descending colon. The main paracolic gutter lies lateral to the colon on each side. A less obvious medial paracolic gutter may be formed, especially on the right side, if the colon possesses a short mesentery for part of its length. The right (lateral) paracolic gutter runs from the superolateral aspect of the hepatic flexure of the colon, down the lateral aspect of the ascending colon, and around the caecum. It is continuous with the peritoneum as it descends into the pelvis over the pelvic brim. Superiorly, it is continuous with the peritoneum which lines the hepatorenal pouch and, through the epiploic foramen, the lesser sac. Bile, pus or blood released from viscera anywhere along its length may run along the gutter and collect in sites quite remote from the organ of origin. In supine patients, infected fluid from the right iliac fossa may ascend in the gutter to enter the lesser sac. In patients nursed in a sitting position, fluid from the stomach, duodenum or gallbladder may run down the gutter to collect in the right iliac fossa or pelvis and may mimic acute appendicitis or form a pelvic abscess. The right paracolic gutter is larger than the left, which together with the partial barrier provided by the phrenicocolic ligament, may explain why right subphrenic collections are more common than left subphrenic collections.

Extraperitoneal subphrenic spaces

There are two potential ‘spaces’ which actually lie outside the peritoneal coverings of the abdomen, but are of clinical relevance because of the possibility that fluid collections will accumulate in them. The right extraperitoneal space is bounded by the two layers of the coronary ligament, the bare area of the liver and the inferior surface of the right dome of the diaphragm. The left extraperitoneal space lies anterior to the left suprarenal gland and upper pole of the left kidney. It contains extraperitoneal connective tissue.

RECESSES OF THE PERITONEAL CAVITY

Peritoneal folds may create fossae or recesses within the peritoneal cavity. These are of clinical interest because a length of intestine may enter one and be constricted by the fold at the entrance to the recess: it may subsequently become a site of internal herniation. The contents of the peritoneal fold may be important if surgical incision is required to reduce such a hernia. Although internal herniation may occur into the lesser sac via the epiploic foramen, the sac is not usually considered to be a peritoneal recess.

Duodenal recesses

Several folds of peritoneum may exist around the fourth part of the duodenum and the duodenojejunal junction forming a number of named recesses (Fig. 64.8).

image

Fig. 64.8 The superior and inferior duodenal recesses. The transverse colon and jejunum have been displaced.

Superior duodenal recess

The superior duodenal recess is occasionally present, usually in association with an inferior duodenal recess. It lies to the left of the end of the fourth part of the duodenum, opposite the second lumbar vertebra, and behind a crescentic superior duodenal fold (duodenojejunal fold). The fold has a semilunar free lower edge which merges to the left with the peritoneum anterior to the left kidney. The inferior mesenteric vein is directly behind the junction of the left (lateral) end of this fold and the posterior parietal peritoneum. The recess varies in size but is commonly 2 cm deep, admitting a fingertip. It opens downwards, its orifice being in the angle formed by the left renal vein as it passes across the abdominal aorta.

Inferior duodenal recess

The inferior duodenal recess is usually present often associated with a superior recess with which it may share an orifice. It lies to the left of the fourth part of the duodenum, opposite the third lumbar vertebra. It sits behind a non-vascular, triangular inferior duodenal fold (duodenomesocolic fold), which has a sharp upper edge. It is usually 3 cm deep, admits one or two fingers and opens upwards towards the superior duodenal recess. It sometimes extends behind the fourth part of the duodenum and to the left, in front of the ascending branch of the left colic artery and the inferior mesenteric vein.

Paraduodenal recess

The paraduodenal recess may occur in conjunction with superior and inferior duodenal recesses. It is rare in adults but is more commonly seen in newborn children. It lies a little to the left and slightly behind of the fourth part of the duodenum, behind a falciform paraduodenal fold. The free right edge of the fold contains the inferior mesenteric vein and ascending branch of the left colic artery, and represents part of the upper left colic mesentery. Its free edge lies in front of the wide orifice of the recess, which faces right.

Retroduodenal recess

The retroduodenal recess is the largest of the duodenal recesses, but is rarely present. It lies behind the third and fourth parts of the duodenum in front of the abdominal aorta. It ascends nearly to the duodenojejunal junction, is 8–10 cm deep, and bounded on both sides by duodenoparietal folds. It has a wide orifice which faces down and to the left.

Duodenojejunal recess

The duodenojejunal or mesocolic recess typically occurs in 20% of adults. When present, it is almost never associated with any other duodenal recesses. It is approximately 3 cm deep and lies to the left of the abdominal aorta, between the duodenojejunal junction and the root of the transverse mesocolon. It is bounded above by the pancreas, on the left by the kidney, and below by the left renal vein. It has a circular opening between two peritoneal folds, and faces down and to the right.

Mesentericoparietal recess

The mesentericoparietal recess is only rarely present. It lies just below the third part of the duodenum and invaginates into the upper part of the mesentery towards the right. Its orifice is large and faces left behind a fold of mesentery raised by the superior mesenteric artery.

Caecal recesses

Several folds of peritoneum may exist around the caecum and form recesses (Fig. 64.9). Paracaecal recesses are common sites for abscess formation following acute appendicitis.

image

Fig. 64.9 The peritoneal folds and recesses in the caecal region.

Superior ileocaecal recess

The superior ileocaecal recess is usually present and best developed in children. It is often reduced and absent in the aged, especially the obese. It is formed by the vascular fold of the caecum, which arches over the anterior caecal artery, supplying the anterior part of the ileocaecal junction, and its accompanying vein. It is a narrow slit bounded in front by the vascular fold, behind by the ileal mesentery, below by the terminal ileum and on the right by the ileocaecal junction. Its orifice opens downwards to the left.

Inferior ileocaecal recess

The inferior ileocaecal recess is well marked in youth but frequently obliterated by fat in adults. It is formed by the ileocaecal fold, which extends from the anteroinferior aspect of the terminal ileum to the front of the mesoappendix (or to the appendix or caecum). It is also known as the ‘bloodless fold of Treves’, although it sometimes contains blood vessels and will often bleed if divided during surgery. If inflamed, especially when the appendix and its mesentery are retrocaecal, it may be mistaken for the mesoappendix. The recess is bounded in front by the ileocaecal fold, above by the posterior ileal surface and its mesentery, to the right by the caecum, and behind by the upper mesoappendix. Its orifice opens downwards to the left.

Retrocaecal recess

The retrocaecal recess lies behind the caecum. It varies in size and extent and ascends behind the ascending colon, often being large enough to admit an entire finger. It is bounded in front by the caecum (and sometimes the lower ascending colon), behind by the parietal peritoneum and on each side by caecal folds (parietocolic folds) passing from the caecum to the posterior abdominal wall. The vermiform appendix frequently occupies this recess when in the retrocaecal position.

Intersigmoid recess

The intersigmoid recess is constant in fetal life and infancy, but may disappear during later development. It lies behind the apex of the V-shaped parietal attachment of the sigmoid mesocolon and is funnel shaped. It is directed upwards and opens downwards. It varies in size from a slight depression to a shallow fossa. Its posterior wall is formed by the parietal peritoneum of the posterior abdominal wall which covers the left ureter as it crosses the bifurcation of the left common iliac artery. Occasionally the recess is within the layers of the sigmoid mesocolon, and is nearer the bowel wall than the mesenteric root. It is probably produced by an imperfect blending of the mesocolon with the posterior parietal peritoneum.

CLINICAL MANAGEMENT OF FLUID COLLECTIONS IN THE PERITONEAL CAVITY

Fluid collections frequently occur within the peritoneal cavity as a result of a wide range of pathological processes. In the absence of any inflammation, peritoneal adhesions or previous surgery, serous fluid is almost always distributed freely between the peritoneal spaces and is not confined to any particular area. Simple ascites, for example, can therefore be drained freely from any convenient dependent part of the peritoneal cavity. This is most commonly performed by blind or ultrasound guided insertion of a catheter into the lower left or right paracolic gutters, which usually readily fill with fluid. The colon and some loops of small bowel may be present, but their relatively mobility ensures that they are very unlikely to be injured during this procedure.

Fluid collections caused by inflammatory processes are often much more viscid because they contain pus, fibrin or blood and are usually associated with peritoneal inflammation which results in, at least transient, peritoneal adhesions. These factors mean that collections may become localized if the flow of fluid is restricted by the partial compartmentalization of the peritoneum. Once collected in a particular ‘space’, this fluid often becomes further confined by ongoing inflammation and may even form a truly walled-off cavity over time. Any of the spaces of the peritoneum may develop a collection, but the subphrenic, subhepatic and pelvic spaces are the commonest since they are most well defined by the fixed peritoneal folds and organs forming their boundaries. These spaces are also the most dependent spaces within the peritoneum in the supine position and consequently any initially free fluid tends to gravitate to them.

Surgical access to the peritoneal spaces is rarely necessary today because of the great advances which have been made in radiologically guided drainage. When necessary, lateral subcostal or intercostal incisions may give adequate access to the subphrenic spaces and the anterior wall of the rectum is also a useful route to access the rectouterine or rectovesical space. Computerized tomography or ultrasound guided drainage offers a much more reliable and versatile method of accessing even difficult spaces such as subhepatic, perihepatic, paracolic or even intermesenteric collections. Posterolateral translumbar or trans-sciatic approaches can be used to access these more difficult areas.

Peritoneal dialysis

The mesothelium resembles vascular endothelium in being a dialysing membrane which fluids and small molecules may traverse. Numerous endocytic vesicles occur near the cell surfaces, and the remaining cytoplasm is poor in organelles, indicating low metabolic activity. Normally the volumes of fluid transmitted by peritoneal surfaces are small, but large volumes may be administered via the intraperitoneal route. Conversely, substances such as urea can be dialysed from blood into fluid circulated through the peritoneal cavity.

Ventriculoperitoneal shunts

The absorptive capabilities of the peritoneum can be used to absorb excess transitional fluids from several sites in the body. The commonest of these is the absorption of cerebrospinal fluid drained from the intracerebral ventricles or the intrathecal space via a fine calibre catheter. The catheter can be placed within the peritoneum with a one way valve preventing reflux of peritoneal fluid into the cerebrospinal fluid. The fluid is then continuously absorbed, maintaining a low pressure within the intrathecal or intraventricular space.

REFERENCES

Coakley FV, Hricak H. Imaging of peritoneal and mesenteric disease: key concepts for the clinical radiologist. Clin Radiol. 1999;54:563-574.

Explains the complex anatomy of the upper abdominal peritoneal fold suspending the stomach, liver and spleen.

Healy JC, Reznek RH. The anterior abdominal wall and peritoneum. In: Butler P, Mitchell A, Ellis H. Applied Radiological Anatomy. Cambridge: Cambridge University Press; 1999:189-200.

Demonstrates the imaging anatomy of the peritoneal spaces and reflections using cross-sectional imaging..

Meyers M. Dynamic Radiology of the Abdomen. In Normal and Pathologic Anatomy. New York: Springer; 1994.

Provides a systematic application of anatomic and dynamic principles to the understanding and diagnosis of intra-abdominal disease..

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