Renal replacement lipomatosis
Chronic left loin pain.
Non-contrast CT of the Abdomen
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The left kidney is mildly enlarged with excess renal sinus fat as well as perirenal fat. this is associated with marked parenchymal atrophic changes and compressed pelvicalyceal system that is also contracted over a branching stag horn stone. Preserved renal outline and mild perirenal fat stranding.
Left vesicoureteric junction small stone.
Multiple right renal small simple cortical cysts and cortical irregularities.
Excess right extrapleural fat on the right side related to the right lower lobe posteriorly. It forms mass appearance of pure fat density smoothly splays the basal segments of the right lower lobe. No evidence of a connection to intraperitoneal contents or a diaphragmatic defect.
This case represents features of renal replacement lipomatosis; which is an advanced massive form of renal sinus lipomatosis, in which renal stone is accompanied by severe renal parenchymal atrophy with mass effect causing attenuation and stretching of the collecting system. It shows increased renal sinus fat as well as perirenal fat and marked atrophic changes of the renal parenchyma with the remaining peripheral part delineates the renal outline. In contrary, the renal parenchyma is preserved in renal sinus lipomatosis.
The presence of atrophic renal parenchyma distinguishes this condition from other causes of fibro-fatty proliferation in and around the kidney, as in obesity or Cushing's disease and excessive corticosteroid therapy.
Excess mass like right extrapleural convex lesion with homogeneous fat density is mostly likely representing pleural lipoma.