Figure 1.

Diagrams of retroperitoneal anatomy. A, Cross‐sectional diagram of the median and left parts of the retroperitoneum according to the tricompartmental theory.3 The retroperitoneum is divided into the anterior pararenal space (green area), perirenal space (yellow area), and posterior pararenal space (gray area) by the anterior renal fascia (red line), posterior renal fascia (purple line), and lateroconal fascia (blue line). Ao, aorta; IVC, inferior vena cava; K, kidney, PM, psoas muscle. B, Cross‐sectional diagram of the same area in panel A, according to the concept of interfascial planes.5 This diagram depicts the interfascial planes as potential spaces among the three compartments: the retromesenteric plane (red area) corresponds to the anterior renal fascia; the retrorenal plane (purple area) corresponds to the posterior renal fascia; and the lateroconal plane (sky‐blue area) corresponds to the lateroconal fascia. Note that the perirenal space is closed medially. C, Longitudinal diagram of the retroperitoneum according to the tricompartmental theory.3 As shown within the dotted circle, the bottom of the perirenal space is patent, and the retroperitoneum below the discontinued renal fasciae (olive area) is ambiguous. D, Longitudinal diagram of the retroperitoneum according to the concept of interfascial planes. The perirenal space is closed inferiorly (open arrow). The combined interfascial plane (pink area) is formed by the inferior blending of the retromesenteric and retrorenal planes and continues into the pelvis. Renal lesions can reach interfascial planes through the perinephric bridging septa (described below) and spread within the combined interfascial plane into the pelvis. E, Aizenstein's advanced diagram of the planes.5 A renal lesion (red area) spreads within the perinephric bridging septa (dotted arrows) and intrudes into the interfascial planes. The lesion can extend contralaterally (red dashed arrow) by way of the retromesenteric plane. F, Our modification of the concept.10, 11 We pointed out that the retrorenal plane, not the posterior pararenal space, lies immediately adjacent to the psoas muscle and quadratus lumborum muscle (QLM) and that the inner border of the posterior pararenal space is limited to the lateral edge of the QLM.10 In addition, we advocated another potential space communicating with the retrorenal plane, which exists behind the posterior pararenal space, and named this the subfascial plane (gold area).10, 11 Panels in this figure are reprinted with permission from the copyright owners (panels A, C: Springer Science+Business Media;3 panels B, E: American Roentgen Ray Society5; panel F: Elsevier11; panel D: Nagai Shoten Co.8, 9 and Wolters Kluwer Health, Inc.10; illustrated by Ishikawa, according to the description by Aizenstein et al.5).