PMC8557040_01
Imaging studies of the right kidney. (a) CT of the abdomen without contrast, axial view. At the level of the mass (outlined by white arrows), the right kidney (RK) is atrophic and there is extensive lipomatous proliferation of the renal sinus fat. The bright linear structure in the middle of the mass is a percutaneous drainage tube. (b) MRI of the abdomen without fat suppression or contrast, coronal T2- weighted image. There is a prominent hyperintense fatty proliferation of the renal sinus fat (outlined by white arrows) displacing the right kidney (RK). There is an associated thin rim of enhancing adjacent renal parenchyma.
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Preoperative abdominal CT and MRI showed an atrophic right kidney with extensive lipomatous proliferation of the renal sinus fat (Figures 1(a) and 1(b)).
Gross photograph of bisected right kidney. The kidney is largely replaced by an extensive fatty proliferation of the renal sinus fat. There is adjacent surrounding residual compressed red-brown renal parenchyma.
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The cut surface revealed a 14.7 x 12.8 x 12.2 cm gray-yellow to white, lobulated, renal sinus lipomatous mass with fibrous septae replacing approximately 85% of the kidney (Figure 2).
Microphotograph of the right kidney. (a) Well-demarcated mature adipose tissue and adjacent renal parenchyma. (b) Renal sinus fat showing inflammatory changes with areas of hyalinization and fat necrosis. (c) The lipomatous proliferation of the renal sinus fat contains fibrous septae and occasional thick-walled vessels with prominent smooth muscle bundles. (d) Rare atypical stromal cell (arrowhead), otherwise no significant cytologic atypia or lipoblasts were identified.
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There was a clear demarcation between adipose tissue and residual renal parenchyma at the periphery (Figures 3(a)-3(d)), which showed relatively mild chronic changes.