gastrointestinal tract and abdomen 2 DISEASES OF THE PERITONEUM AND RETROPERITONEUM Amanda K. Arrington, MD, and Joseph Kim, MD Anatomy and Physiology: Peritoneum transverse mesocolon, on the other hand, is the mesentery of the transverse colon and suspends this structure from anatomy the posterior abdominal wall. The root of the transverse The word peritoneum is derived from the Greek terms peri mesocolon extends across the descending duodenum and (“around”) and tonos (“stretching”). The peritoneum, which the head of the pancreas and continues along the inferior lines the innermost surface of the abdominal wall and the border of the body and tail of the pancreas. The transverse majority of the abdominal organs, consists of a layer of mesocolon is continuous with the duodenocolic ligament on dense stroma covered on its inner surface by a single sheet the right and with the phrenicocolic and splenorenal liga- of mesothelial cells. In men, the peritoneum is completely ments on the left. Finally, the sigmoid mesocolon attaches enclosed, whereas in women, the peritoneum is open to the the sigmoid colon to the posterior pelvic wall. This mesen- exterior only at the ostia of the fallopian tubes. The perito- tery, which has an inverted V-shape confi guration, with its neum is divided into two components: the parietal and the apex lying anterior to the bifurcation of the left common ilia c visceral peritoneum [see Figure 1]. The parietal peritoneum artery, contains both sigmoid and hemorrhoidal vessels, covers the innermost surface of the abdominal walls, the lymph nodes, nerves, and abundant fat tissue.3 inferior surface of the diaphragm, and the pelvis. The vis- ceral peritoneum, on the other hand, covers the majority physiology of the intraperitoneal organs [see Table 1] and the anterior The blood supply and innervation of the peritoneum aspect (only) of the retroperitoneal organs [see Table 1]. As depend on whether it is visceral peritoneum or parietal peri- shown in Figure 1, the intraperitoneal organs are suspended toneum. The blood fl ow to the visceral peritoneum is sup- by ligaments of peritoneum within the abdomen that have plied by the splanchnic blood vessels, whereas the parietal previously been identifi ed by Meyers and colleagues [see peritoneum is supplied by intercostal, subcostal, lumbar, Figure 1 and Table 1].1 The spread of infection, as well as the and iliac vessels. Correspondingly, the innervation of the spread of a primary tumor or metastatic disease, can be pre- two components is divided: the visceral peritoneum is sup- dicted based on subdivisions of the abdominal compart- plied by nonsomatic nerves, whereas the parietal peritone- ments created by these peritoneal ligamentous structures of um is supplied by somatic nerves. This detail is important the abdomen. when evaluating for pain. Visceral pain is poorly localized The omentum (greater and lesser omentum) is a well- and vague and is generally caused by stretching, distention, vascularized double fold of peritoneum with fat that torsion, and twisting motion. On the other hand, parietal contributes to the control of intra-abdominal infection and pain is caused by direct stimulation of nerve fi bers and is infl ammation. The omentum aids in sealing off perforations described as sharp and well localized. (as in perforated ulcer or perforated appendicitis) and controls infl ammation (i.e., unruptured appendicitis). The peritoneum is a bidirectional, semipermanent bio- Additionally, the omentum delivers phagocytes that destroy membrane that controls the amount of fl uid in the perito- unopsonized bacteria. Thus, the omentum has multiple neal cavity. The peritoneal cavity typically contains less than functions in the body’s defense system against infection. 100 mL of sterile peritoneal fl uid. This peritoneal fl uid may The small bowel mesentery and transverse mesocolon are act as both part of the local defense system and a lubricant also complex peritoneal folds that originated from the dorsal for intraperitoneal organs. In certain disease states, such as and ventral midline mesenteries early in development and nephrotic syndrome, congestive heart failure, cirrhosis, or are considered part of the peritoneum. The small bowel portal hypertension, the amount of peritoneal fl uid may mesentery suspends the jejunum and ileum from the poste- increase from the normal less than 100 cc protective amount rior abdominal wall. This mesentery contains the superior to several liters in volume [see Ascites, below]. mesenteric vessels, lymph nodes, nerves, and fat tissue. Its Circulation of peritoneal fl uid is driven in part by the root originates at the duodenojejunal junction and extends movement of the diaphragm. The peritoneal cavity can downward in an oblique direction across the aorta, inferior absorb peritoneal fl uid through two different systems. vena cava, right ureter, and psoas muscle to the right iliac Substances smaller than 2 kDa are absorbed through the fossa at the ileocecal junction. Across the mesenteric root, peritoneal mesothelial venous pores directly into the portal the small bowel mesentery is in anatomic continuity with circulation.4 Conversely, larger particles (> 2 kDa) are the extraperitoneal anterior pararenal space, thus providing absorbed through the peritoneal mesothelial lymphatics a channel for the spread of disease.2 As a result of its shorter and enter the lymphatic system via the thoracic duct. This length (15 cm) in comparison with the much longer length particular route of absorption plays an important role in of the small bowel itself (6 to 8 m), the small bowel mesen- controlling abdominal infections and has been shown to tery has a pleated appearance along its intestinal border. The propagate the metastatic spread of certain cancers. ACS Surgery © 2014 Decker Intellectual Properties Inc DOI 10.2310/7800.2257 07/14 SSurg_Gastro_tid2257.inddurg_Gastro_tid2257.indd 1 44/3/2014/3/2014 112:21:302:21:30 PPMM gastro diseases of the peritoneum and retroperitoneum — 2 Liver Visceral Peritoneum Parietal Peritoneum Pancreas Stomach Mesocolon Duodenum Colon Small Bowel Mesentery Greater Omentum Small Intestine Douglas Pouch Bladder Rectum Figure 1 Peritoneal components. The peritoneum consists of parietal peritoneum and visceral peritoneum. Visceral peritoneal covers the surface of intraperitoneal organs. The omentum and mesentery are also peritoneal structures. Anatomy and Physiology: Retroperitoneum iliac crest inferiorly. Organs are classifi ed as retroperitoneal The retroperitoneum is defi ned as the space between the in location if they have no peritoneal lining whatsoever or posterior parietal peritoneum and the posterior body wall. have peritoneum on their anterior surface only [see Table 1]. Although it has no specifi c delineating anatomic structures, Furthermore, structures that are not suspended by mesen- the retroperitoneal space is bound anteriorly by the poste- tery in the abdominal cavity and that lie between the pari- rior refl ection of the peritoneum, superiorly by the dia- etal peritoneum and the abdominal wall are also classifi ed phragm, and inferiorly by the levator ani muscles. This as retroperitoneal in location; this includes the duodenum, space also includes the lumbar fossa, extending from the ascending colon, and descending colon [see Figure 2]. 12th thoracic spine superiorly to the base of the sacrum and Because of the compliance of the anterior border of the ACS Surgery 07/14 SSurg_Gastro_tid2257.inddurg_Gastro_tid2257.indd 2 44/3/2014/3/2014 112:21:302:21:30 PPMM gastro diseases of the peritoneum and retroperitoneum — 3 Table 1 Abdominal Components Retroperitoneal operative approaches may be benefi cial for a number of reasons. First, it avoids entrance in to the Intraperitoneal organs peritoneum and, thus, decreases manipulation and the risk Gastrointestinal Stomach of injury to intra-abdominal organs. Minimal manipulation Small intestine of the small intestine, for instance, signifi cantly decreases Transverse colon complications such as postoperative ileus. Given successful Liver avoidance of entering the peritoneum, intra-abdominal Endocrine 7 Spleen adhesions are also minimized. Retroperitoneal structures Gastrointestinal Diseases of the Peritoneum Duodenum Ascending colon ascites Descending colon Pancreas Pathophysiology and Etiology Vascular Inferior vena cava Ascites is the pathologic accumulation of fl uid within the Aorta peritoneal cavity. The primary cause of nonmalignant asci- Lymphatics tes accumulation is liver disease (cirrhosis and portal hyper- Iliac arteries Renal tension), which accounts for 85% of cases of ascites in the Kidneys United States. Other causes of ascites are listed in Table 2 Ureters [see Table 2]. In cirrhotic patients, the onset of ascites is an Bladder overall poor prognostic factor as patients are more likely Endocrine Adrenals to develop spontaneous bacterial peritonitis (SBP), renal Sexual (hepatorenal) failure, decreased quality of life, and decreased Seminal vesicles overall survival.8 Vas deferens Ovaries Accumulation of ascites in patients with cirrhosis is Vagina secondary to the combination of renal sodium and water Other retention with portal hypertension [see Figure 3]. Driven Nerves by activation of the renin-angiotensin-aldosterone system, Peritoneal ligaments and mesenteries renal sodium retention is the result of proximal and distal Ligaments renal tubule sodium reabsorption. The renin system is acti- Splenorenal vated in response to decreased circulating blood volume Gastrohepatic