GENERAL ARRANGEMENT OF THE PERITONEAL CAVITY
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 (p. 1133).
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 (adrenal) 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, c.3 cm 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.
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.
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.
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. These spaces usually readily fill with fluid and although the colon and some loops of small bowel may be present, their relatively mobility results in very little risk of injury to them.
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 one '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.
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, the remaining cytoplasm being 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.
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.
RECESSES OF THE PERITONEAL CAVITYPeritoneal 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 (Fig. 69.10)
Several folds of peritoneum may exist around the fourth part of the duodenum and the duodenojejunal junction forming several recesses.
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 is c.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 c.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 (Fig. 69.11)
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.
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.
The duodenojejunal or mesocolica recess occurs in c.20% of adults. When present, it is almost never associated with any other duodenal recesses. It is c.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.
Figure 69.10 The superior and inferior duodenal recesses. The transverse colon and jejunum have been displaced. (After Jonnesco, from Poirier P, Charpy A 1901 Traite d'Anatomie Humaine. Paris: Masson et Cie.)
Figure 69.11 The paraduodenal recess.
The mesentericoparietal recess is only rarely present in adults. 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 (Fig. 69.12)
Several folds of peritoneum may exist around the caecum and form recesses. Paracaecal recesses are common sites for abscess formation following acute appendicitis.
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
Figure 69.12 The peritoneal folds and recesses in the caecal region.
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 recessThe 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 recessThe 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.