Figure 4.

Other retroperitoneal diseases. A, B, A 54‐year‐old man with infectious colitis probably from Aeromonas hydrophila. Note the marked fluid collection in the retromesenteric (white thick arrows), lateroconal (white arrowheads), and retrorenal (black triangles) planes and clear checkmark signs (gold curved arrows). Additionally, note that fluid collection within the medial part of the retrorenal plane is located close to the psoas muscle and quadratus lumborum muscle as well as in panels C and F (purple arrows). He died 10 h after admission despite emergent right colostomy and intensive care. C, A 75‐year‐old man with obstructive acute pyelonephritis. Note the fluid collection within the retrorenal plane (black triangles and purple arrows) with the thickened perinephric bridging septa (thin dotted white arrows) and strands (thin white arrows) in the posterior pararenal space. D, A 36‐year‐old woman with barotraumas due to transtracheal jet ventilation. Massive pneumoretroperitoneum spreads in the retromesenteric plane (white thick arrows) and appears as mobilizing colon and duodenum by Cattell–Braasch maneuver (curved red arrows). E, A 65‐year‐old man with retroperitoneal abscess accumulated within the retromesenteric (white thick arrows), lateroconal (white arrowhead), retrorenal (black triangle), and subfascial (gold curved arrow) planes, speculated to be a hematogenously disseminated abscess after sepsis. Note the strands (thin white arrow) in the posterior pararenal space. F, A 69‐year‐old man with ruptured abdominal aortic aneurysm. Retroperitoneal hematoma in the retromesenteric plane (thick white arrows) spreads beyond the midline (red dotted arrow) and elevates the duodenum (orange arrow). Note the retroperitoneal hematoma within the retrorenal (black triangle and purple arrows), lateroconal (white arrowhead), and subfascial (gold curved arrow) planes and the perinephric bridging septa (thin dotted white arrow).