Zoning inside the renal fascia: The anatomical relationship between the urinary system and perirenal fat

Abstract

Objectives: To examine the anatomical relationship between the urinary system and perirenal fat, and to clarify the zoning inside the renal fascia.

Methods: Using computed tomography images from 50 men, we examined perinephric veins to reveal vessel communication in perirenal fat. Nine cadavers were dissected to investigate connective tissue continuity and vessel communication inside the renal fascia. Eight retroperitoneal specimens were macroscopically observed: four from the anterior and four from the posterior aspects. One specimen was used to obtain retroperitoneal transverse sections to study macroscopic anatomy and histology.

Results: Perinephric veins were classified into four types (superior, middle, inferior and lateral) using computed tomography. Most of the inferior perinephric veins were connected to the ipsilateral gonadal vein. In the cadaveric study, the superior and middle perinephric veins communicated with veins deriving from the ipsilateral adrenal gland. A fibrous connective tissue gap between perirenal fat and renal hilar fat was observed in posterior aspect dissection. From the gap, we could dissect the urinary system from perirenal fat en bloc along with a thin fibrous connective tissue layer. Communicating vessels between perirenal fat and the urinary system were rare.

Conclusions: Our results suggest that perirenal fat belongs to the connective tissue of the gonad and the adrenal gland. The urinary system is separate from perirenal fat, and is located on the dorsal side inside the renal fascia. This concept of zoning inside the renal fascia is valuable particularly in retroperitoneoscopic donor nephrectomy.

Keywords: perinephric vein; perirenal fat; renal fascia; retroperitoneal anatomy; retroperitoneoscopy.

Fig. 1

Intraoperative retroperitoneoscopic view of the left donor nephrectomy in a 61‐year‐old man. (a) The Ur, periureteral fat and ureteral feeding vessels (asterisks) were covered by a thin fibrous connective tissue sheath. This ureteral sheath was observed to exist separately behind PeRF, including the GV. (b) The ureteral sheath connected to the thin fibrous connective tissue around RHF (arrowheads). The RC was initially exposed to a fibrous connective tissue gap between PeRF and RHF (two‐way arrow). (c) PeRF was separated from the RC along with the thin fibrous connective tissue layer. Communicating vessels between PeRF and the RC were rare. GV, gonadal vein; PeRF, perirenal fat; RC, renal capsule; RHF, renal hilar fat; Ur, ureter.

Fig. 2

CT images of perinephric veins. (a–f) CT images (axial view) of a 45‐year‐old man. The IPV connected to the GV (asterisk). (g,h) 3‐D reconstructed CT images of a 45‐year‐old man (the same patient in a–f; arrows a–f in g correspond to the section in a–f). The MPV connected to the left emissary vein of the AG and the IPV to the GV at the lower pole of perirenal fat (asterisk). The superior and LPVs were poorly reconstructed. (i,j) 3‐D reconstructed CT images of a 60‐year‐old man. The MPV connected to the left RV and the IPV to the GV in the IC (asterisk). The superior and LPVs were poorly reconstructed. AG, adrenal gland; Ao, aorta; AV, adrenal vein; B, bladder; CIA, common iliac artery; DC, descending colon; GV, gonadal vein; IC, inguinal canal; K, kidney; RF, renal fascia; RV, renal vein; S, spleen; SpeV, spermatic vein; Ur, ureter.

Fig. 3

Schema and macroscopic anatomy of perinephric veins. (a) Anterior aspect. Schema of perinephric veins distribution and frequency. Numbers in this figure represent the frequencies of perinephric veins shown in Table 1. Line thickness refers not to the actual size, but to the frequency of veins. (b) The retroperitoneum of a male cadaver (60 years‐of‐age at death). The right urinary system and perirenal fat were removed to show perinephric veins. Several fine branches from perinephric veins were observed. Arteries ran along perinephric veins and branches. The SPV and the MPV had several communicating veins, with the veins deriving from the AG (stars). In this image, the LPV had already been removed with perirenal fat. AG, adrenal gland; Ao, aorta; AV, adrenal vein; GV, gonadal vein; IC, inguinal canal; IPhV, inferior phrenic vein; K, kidney; LV, lumbar vein; RA, renal artery; RV, renal vein; SV, splenic vein; T, testis; Ur, ureter; VD, vas deferens.

Fig. 4

Macroscopic anatomy and histology of the retroperitoneum. (a–d) The retroperitoneum of a female cadaver (78 years‐of‐age at death) observed from the posterior aspect. (a) Macroscopic anatomy of the right retroperitoneum from the posterior aspect after removal of the skin, muscles and vertebral bodies. (b) PaRF and the posterior RF were removed. A fibrous connective tissue gap was observed between PeRF and RHF (arrowheads). (c) From the gap, the posterior aspect of PeRF was removed, along with the thin fibrous connective tissue layer around the RC. The renal capsular veins ran on the surface of the kidney and continued to the veins in RHF (red arrows). Communicating vessels from PeRF to the RC were few (black arrow). (d) The right urinary system was removed en bloc with RHF. The Ur, periureteral fat and ureteral feeding vessels were covered by a thin fibrous connective tissue sheath. Ureteral feeding vessels communicated with the vessels in RHF. The ureteral sheath continued to the thin fibrous connective tissue around RHF. The renal capsular veins ran on the surface of the RC and continued to veins in RHF (red arrows). (e–j) The retroperitoneum of a male cadaver (73 years‐of‐age at death) observed in transverse section. (e) A transverse section of the left retroperitoneum. (f) Histology of the white square section in Figure 3e (Masson’s trichrome stain). (g) High magnification of the red square section in Figure 3f (Masson’s trichrome stain). The RC could be confirmed between PeRF and the renal cortex, but not between RHF and the renal cortex (the transition point is indicated by a black arrow). Stars (☆), bridging septa; asterisks (＊), border of the RHF. (h) A transverse section of the right retroperitoneum. (i) Histology of the white square section in Figure 3h (Masson’s trichrome stain). (j) High magnification of the red square section in Figure 3i (Masson’s trichrome stain). The renal capsular veins ran in the internal space of the RC (red arrows). Communicating vessels between PeRF and the RC were not identified. Stars (☆), bridging septa. Ao, aorta; DC, descending colon; Di, diaphragm; GV, gonadal vein; K, kidney; PaRF, pararenal fat; PeRF, perirenal fat; PM, psoas muscle; Pr, peritoneum; RA, renal artery; RC, renal capsule; RHF, renal hilar fat; RV, renal vein; Ur, ureter.

Fig. 5

The retroperitoneum of a male cadaver (63 years‐of‐age at death) observed from the posterior aspect. (a) The macroscopic anatomy of the retroperitoneum from the posterior aspect after removal of the skin, back muscles and vertebral bodies. (b) The left retroperitoneal posterior aspect. The Ao, the IVC, and external and internal vessels were cut along the white dashed lines shown in (a) and removed. The posterior side of PeRF was removed along the black dashed circle shown in (a). The Ur, periureteral fat and ureteral feeding vessels were covered by a thin fibrous connective tissue sheath. The GV and the IPV connected at the lower pole of PeRF. The ureteral sheath ran separately behind PeRF. (c) After removing the left urinary system, PeRF converged toward the caudal side along the gonadal vessels (arrow heads). AG, adrenal gland; Ao, aorta; GA, gonadal artery; GV, gonadal vein; K, kidney; PaRF, pararenal fat; PeRF, perirenal fat; RA, renal artery; RHF, renal hilar fat; RV, renal vein; Ur, ureter.

Fig. 6

A new anatomical concept of zoning inside the RF. These figures are drawn based on the concept of “interfascial plane.” ⁹ , ¹⁰ , ¹¹ The gray area represents a potential space within a multilayered membranous structure. (a–e) Transverse sections of parts indicated by arrows a–e in (f). The urinary system, RHF and periureteral fat (orange area) were separated from PeRF (green area) by a thin fibrous connective tissue (gray area). A gap between PeRF and RHF is indicated by an arrowhead in (b,c). The Ur, periureteral fat and ureteral feeding vessels were covered by a thin fibrous connective tissue sheath. The ureteral feeding vessel is indicated by an asterisk in (c–f). AG, adrenal gland; Ao, aorta; BS, bridging septum; GV, gonadal vein; K, kidney; PaRF, pararenal fat; PeRF, perirenal fat; PM, psoas muscle; Pr, peritoneum; RA, renal artery; RCV, renal capsule vein; RF, renal fascia; RHF, renal hilar fat; RV, renal vein; Ur, ureter.