The sigmoid mesocolon is a peritoneal ligament that attaches the sigmoid colon to the posterior pelvic wall and contains the hemorrhoidal and sigmoid vessels. The most common pathologic process involving this structure is acute diverticulitis. Perforated cancer and Crohn disease also may cause inflammation within the sigmoid mesocolon. Knowledge of the peritoneal spaces and the routes of communication between them is important.
The transverse mesocolon divides the peritoneum into the supramesocolic and inframesocolic spaces; the bilateral paracolic and pelvic spaces are also peritoneal spaces Fig 8a. Most of the time, slow fluid accumulation in the peritoneal cavity may be localized to one or two spaces.
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Rapid accumulation of fluid, such as occurs in cases of trauma or acute pancreatitis, may overcome the natural boundaries of the peritoneal spaces and spill into multiple spaces. Supramesocolic peritoneal spaces. The right subphrenic space RSP and the superior LSs and inferior LSi recesses of the lesser sac are separated by a peritoneal fold that contains the left gastric artery.
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The left and right supramesocolic spaces usually communicate freely with one another and include the perihepatic, left subphrenic, and perisplenic spaces Fig 8a , 8b. The phrenicocolic ligament is a relative but incomplete impediment to the spread of pathologic processes from the left paracolic gutter to the left subphrenic space Fig 3.
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The right supramesocolic spaces include the right subphrenic subdiaphragmatic space, the Morison pouch subhepatic or hepatorenal space , and the lesser sac omental bursa. The right subphrenic space is separated from the left perihepatic space by the falciform ligament, which varies in size and may not always serve as a barrier to the spread of disease Fig 2.
The right subhepatic space is an important site of fluid collections resulting from liver injuries because it is the most gravity-dependent space at this site Fig 8c. The lesser sac contains a superior recess located above the peritoneal reflection of the left gastric artery that is in close proximity to the caudate lobe and has a boomerang-shaped recess and a larger inferior recess that lies between the stomach and the pancreatic body.
The superior and inferior recesses are separated by a peritoneal fold that accompanies the left gastric artery Fig 9a. Sometimes, the inferior recess communicates with a potential space between the leaves of the greater omentum. On the right side, the inferior recess communicates with the subhepatic space through the foramen of Winslow. Thus, it is possible for bowel to herniate into the lesser sac through the foramen of Winslow Fig 9b. Lesser sac. The recesses are separated by the left gastric artery arrow , and the foramen of Winslow allows communication between the lesser sac and the subhepatic space SHS.
Fluid is seen in the anterior pararenal space APS , a common location for fluid collections in patients with acute pancreatitis. Linear hypointense MR imaging—related artifacts are seen in the anterior pararenal space, and the hepatoduodenal HDL and gastrohepatic GHL ligaments, two contiguous structures, are clearly depicted.
The foramen is marked posteriorly by the hepatic vessels black arrow. The presence of a foramen of Winslow hernia was confirmed at surgery. The right and left inframesocolic spaces are separated from the supramesocolic spaces by the transverse mesocolon and from the paracolic gutters laterally by the ascending or descending colon. The smaller right inframesocolic space is limited inferiorly by the attachment of the small bowel mesentery to the cecum; collections in this space generally do not extend into the pelvis Fig However, the larger left inframesocolic space communicates freely with the pelvis.
Figure 10 Inframesocolic peritoneal spaces. Coronal reformatted CT image, obtained in a year-old man who underwent heart transplantation and subsequently developed retroperitoneal hemorrhage, shows the left LIMC and right RIMC inframesocolic spaces, which are separated by the small bowel mesentery white arrow.
The left inframesocolic space and the right RPC and left LPC paracolic spaces communicate with the pelvis black arrows , whereas the right inframesocolic space does not. The paracolic spaces gutters are located lateral to the peritoneal reflections of the left and right sides of the colon Fig 8a.
The right paracolic gutter is larger than the left and communicates freely with the right subphrenic space. The connection between the left paracolic gutter and the left subphrenic space is partially limited by the phrenicocolic ligament. Both the right and left paracolic gutters communicate with the pelvic spaces. In men, the most gravity-dependent site for fluid accumulation is the rectovesical space. In women, it is the retrouterine space the pouch of Douglas Fig Anteriorly, the medial umbilical folds, which contain the obliterated umbilical arteries, divide the pelvic spaces into lateral and medial compartments.
On each side, the inferior epigastric artery divides the lateral pelvic compartments into lateral and medial inguinal fossae, the sites of direct and indirect inguinal hernias, respectively. Retrouterine space pouch of Douglas. The retrouterine space POD , the most gravity-dependent site for fluid accumulation in women, and the vesicouterine pouch arrow also are highlighted by dialysate solution.
The retroperitoneum is divided into three distinct compartments: the posterior pararenal space, bounded by the transversalis fascia posteriorly; the anterior pararenal space, bounded by parietal peritoneum anteriorly; and the perirenal space, bounded by the perirenal fascia Fig 12a , 12b. The anterior pararenal space is composed of structures that mainly develop from the dorsal mesentery, namely the pancreas and the right and left portions of the colon.
The perinephric space is outlined anteriorly by Gerota fascia and posteriorly by Zuckerkandl fascia and contains the kidneys and adrenal glands. The perinephric space contains bridging septa and a network of lymphatic vessels that allow the spread of disease to or from adjacent spaces. The perinephric space has an inverted cone shape caused by the ascent of the kidneys from the pelvis. It is usually, but not always, cut off inferiorly by the fusion of Gerota and Zuckerkandl fascias and does not extend into the pelvis.
The small posterior pararenal space is bound by the transversalis fascia posteriorly and the lateroconal fascia laterally. It contains two fat pads that lie ventral and posterolateral to the quadratus lumborum muscle.
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In patients with acute pancreatitis, the Grey-Turner sign is caused by spread of disease from the anterior pararenal space to the area between the leaves of the posterior renal fascia and, subsequently, the lateral edge of the quadratus lumborum muscle 10 , Communication with the posterior pararenal space and the structures of the flank wall may be established.
The superior and inferior lumbar triangles, sites of anatomic weakness in the flank wall, may structurally predispose this area to development of lumbar hernias Fig 12c. Retroperitoneal anatomy. The anterior pararenal space APS is mostly free of gas. Note that it is possible for disease to extend from the posterior pararenal space PPS , through the quadratus lumborum muscle arrow , and into the subcutaneous space, the site of an inferior lumbar hernia as well as the Grey-Turner sign, which manifests as lateral abdominal discoloration in patients with severe pancreatitis.
Extravasated air has dissected into the Morison pouch MP , a finding indicative of abrupt accumulation of air or fluid that crosses the peritoneal and retroperitoneal spaces. A fourth space surrounds the aorta and inferior vena cava.
This space is limited laterally by the perirenal spaces and ureters and extends superiorly into the posterior mediastinum. Some diseases, such as retroperitoneal fibrosis, are predominantly confined to this space, whereas others, such as hemorrhage from a leaking aortic aneurysm, extend interfascially According to recent studies, the perirenal fascia is not made up of distinct unilaminated fascia; rather, it is composed of multiple layers of variably fused embryonic mesentery, creating potential spaces between the retroperitoneal spaces.
These potential spaces are represented by the retromesenteric, retrorenal, lateral conal, and combined fascial planes Fig 13 13 , Interfascial spread. Although the perirenal space is cut off by the fusion of Gerota and Zuckerkandl fascias inferiorly, it is possible for disease to extend along the combined interfascial plane.
The retromesenteric plane is a potentially expansile plane located between the anterior pararenal space and the perirenal space Fig 12a. It communicates across the midline and is a major source of fluid spread in patients with pancreatitis. The presence of fluid in the retromesenteric plane is often erroneously attributed to the anterior pararenal space. The retrorenal plane is a potentially expansile plane located between the perirenal space and posterior pararenal space Fig 12a. It does not cross the midline because it is interrupted by the great vessel space.
Fluid collections in the anterior pararenal space and the retromesenteric plane may extend to the retrorenal space. The retrorenal plane combines with the retromesenteric plane inferiorly to form the combined interfascial plane, which extends into the pelvic retroperitoneum Fig 13 14 , The interfascial plane extends into the pelvis anterolaterally to the psoas muscle and is a route for the spread of some infections, such as tuberculosis.
The lateral conal interfascial plane is a potentially expansile space between the layers of the lateroconal fascia that communicates with the retromesenteric and retrorenal interfascial planes at the fascial trifurcation. The term subperitoneal spread refers to the spread of fluid or tumor from its site of origin along the peritoneal ligaments eg, pancreatic inflammation or cancer that spreads along the peritoneal ligaments Figs 2 , 6 16 , Tumors and fluid collections may spread across the peritoneal ligaments subperitoneal spread to involve several contiguous organs.
Interfascial spread is the spread of fluid within the layers of the retroperitoneal fascia and is a common route of disease spread across the midline within the retroperitoneum and from the abdomen to the pelvis, such as along the retromesenteric, retrorenal, and interfascial planes Fig 14 13 , The right retromesenteric plane extends superiorly at the level of the right inferior coronary ligament and the bare area of the liver, and it communicates with the liver hilum through the subperitoneal space of the hepatoduodenal ligament.
On the left side, the retrorenal plane and the perirenal space extend to the left diaphragm. As was mentioned earlier, fluid collections in the paracolic and left inframesocolic spaces may communicate with the pelvic spaces Fig Interfascial spread is another method of communication between the abdomen and pelvis and also allows communication across the midline through the retromesenteric plane.
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Interfascial spread of fluid in a year-old man with acute rupture of an abdominal aortic aneurysm. Interfascial spread allows communication between the abdomen and pelvic retroperitoneum. A variety of pathologic conditions may demonstrate nonspecific radiologic features. Understanding the anatomic relationships and pathologic processes of the peritoneum is essential to provide accurate diagnosis.
Multidetector CT studies performed with isotropic imaging with coronal and sagittal reformations fully delineate the peritoneal anatomy and extent of disease. Disclosures of Potential Conflicts of Interest. Other financial activities: consultant for Repligen.
For this journal-based CME activity, authors K. Abbreviations: PACE prospective acquisition correction. Downloaded , times Altmetric Score. Home RadioGraphics Vol. Address correspondence to T. Patel Margaret A.
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