The dissectable, potential planes ofthe bilateral posterior renal fascia communicate with the bilateral retromesen-teric planes and lateroconal space, typically without involving perirenal fat and posterior pararenal fat (Figs. 8112, 8-113, 8-115). In the presence of ascites, fluid in the posterior peritoneal recesses may have a forktailed or wishbone configuration posterior to the kidney mimicking retrorenal and lateroconal plane fluid collec-
tions.34535'150 This is probably related to the extent in which the colon and mesocolon fuse laterally with the primary posterior peritoneum. Cranially, the retrorenal plane extends medially, posterior to the perirenal fat. Caudally, its medial extent is more laterally, adjacent to the quadratus lumborum muscle. Distally, the continuation of either the combined interfascial plane, formed by the inferior blending of the anterior renal, posterior renal, and lateroconal fascia or the retrorenal plane, is to
Fig. 8—109. Anatomic landmarks of the different components of the anterior pararenal space in a patient with pancreatitis.
(a) At the level of the pancreatic tail, the fusion fascia (arrows) dorsal to the transverse mesocolon is continuous with the left retromesenteric plane (white arrowheads), behind the cranial extent of the left colonic compartment. Note the vessels within the fat (black-and-white arrowheads) representing the continuity between middle colic vessels in the transverse mesocolon and left colic vessels within the left colonic compartment. DC = descending colon; TC = transverse colon.
(b) More caudally, at the level of the renal veins, the left colonic compartment contains the left colic vessels laterally (black arrows) and the inferior mesenteric vein medially (white arrow). Note the accentuated left retromesenteric plane (white arrowheads). The transverse mesocolon (asterisk), containing the middle colic vessels (black-and-white arrowhead), is attached anterior to the pancreatic neck (P).
(c) At the level of the lower pole of the kidneys, the upper extension of the right colonic compartment is indicated by the vessels (black arrow) medial to the hepatic flexure (HF), representing the continuity between middle and right colic vessels. The pancreatic head (P) is located posterior to the right colonic compartment and transverse mesocolon (asterisk). Note left colic vessels (black arrowhead) in the left colonic compartment medial to the descending colon (DC). White arrow = inferior mesenteric vein; white arrowheads = left retromesenteric plane.
(d) At the level of the aortic bifurcation, the right colic vessels are continuous with the ileocolic vessels (white arrows), located medial to the cecum (C), within the caudal extension of the right colonic compartment. The left colic vessels (black arrowheads), within the left colonic compartment, are continuous with the branches from the inferior mesenteric vein (black-and-white arrowhead) within the cranial extension of the mesosigmoid. DC = descending colon; white arrowheads = caudal extent of left retromesenteric plane.
Fig. 8-110. Patient with resolving exudative pancreatitis.
(a) Cranially, fluid (F) is located anterior to the pancreatic tail within the left pancreaticoduodenal compartment. Note the transverse mesocolon (black arrow) and upper extension of the left colonic compartment (black-and-white arrow), anterior and lateral to the fluid collection, respectively.
(b) At the level of the pancreatic head (P), the fluid collection (F) is continuous with the left retromesenteric plane laterally and with the base of the transverse mesocolon (asterisk) medially. HF = hepatic flexure; white arrowheads = vessels in left colonic compartment, medial to descending colon (DC).
(c) More caudally, the collection (black F) within the base of the transverse mesocolon extends anteriorly and continues laterally within the cranial extension of the right retromesenteric plane (white F). The left retromesenteric collection (arrowheads) demarcates the left perirenal space posteriorly from the left colonic compartment anteriorly. Note the inferior mesenteric vein (white arrow) within the medial extension of the left colonic compartment. AC = ascending colon; DC = descending colon; white arrowhead = left colic vessels in left colonic compartment.
(d) Below the pancreatic head, the right and left retromesenteric fluid collections (F) continue posterior to the right and left colonic compartment, respectively. AC = ascending colon; DC = descending colon; white arrow = inferior mesenteric vein; white arrowheads = left colic vessels in left colonic compartment.
MÊ ■ m
Fig. 8—111. Communications of left pancreaticoduodenal space to left retromesenteric colonic space.
After catheter drainage of pancreatic abscess, contrast around the pancreas in (a) has spread in (b) to the left retromesenteric space (arrow).
the infraconal compartment133 or lateral pathway,159 abutting the psoas muscle, lateral from the ureter and the sigmoid mesocolon into the pelvis134 (Fig. 8-112). Inferior to the cone of perirenal fat, posterior extension of retrorenal fluid between the quadratus lumborum fat pad and posterior pararenal fat can frequently be seen on CT through a well-defined defect near the lumbar triangle, the so-called inferior lumbar pathway34 (Fig. 8-112). If the subcutaneous tissues in the flank are reached via this route or the nearby posterior pararenal space,91 the spread of fluid may be responsible for flank discoloration (Grey Turner sign).
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