Alien calcification: A rare case report of renal squamous cell carcinoma with renal replacement lipomatosis

Squamous cell carcinoma (SCC) of the kidney is an exceedingly rare entity due to the absence of native squamous cells in the renal pelvis. It occurs secondary to squamous metaplasia as a result of chronic irritation in the setting of renal calculi. Renal replacement lipomatosis is a rare and benign entity characterized by the proliferation of pelvic sinus fat secondary to staghorn calculi. The chief differential for these conditions is xanthogranulomatous pyelonephritis (XGP) which requires imaging as well as histopathology for differentiation. We present the case of a 56-year-old man presenting with low-grade fever, left lumbar pain, and significant weight loss for 6 months. This rare case report highlights the importance of imaging in diagnosis and prognostication, wherein findings of invasive, enhancing soft tissue and minimal hydronephrosis on computed tomography suggested renal SCC over XGP.