Sarcomatoid Squamous Cell Carcinoma of the Renal Pelvis Masquerading as Emphysematous Pyelonephritis with Staghorn Calculus.

Background: Staghorn calculi are well-established risk factors for recurrent urinary tract infections (UTIs) and subsequent renal deterioration. Less commonly, long-term urothelial irritation from a calculus may also pose a risk of malignant transformation.

Case Presentation: A 77-year-old male with multiple medical comorbidities presented with a chronic right renal pelvic staghorn calculus and findings concerning for emphysematous pyelonephritis. He was subsequently taken to the operating room for a planned laparoscopic right nephrectomy. Final pathology analysis revealed sarcomatoid squamous cell carcinoma (SCC) of the renal pelvis with superimposed pyelonephritis and renal abscesses. Preoperative imaging was not suggestive of malignancy.

Conclusion: Although SCC of the urothelium can be caused by chronic irritation, its presentation is usually isolated to the lower urinary tract and is rarely encountered in the renal pelvis. Our patient's presentation with sarcomatoid SCC is an even rarer entity. Chronic staghorn calculi must be considered as a potential risk factor for the development of both UTI and malignant urothelial transformation.