Upper tract urothelial carcinoma mimicking emphysematous pyelonephritis: a diagnostic challenge case report.

Background: Upper tract urothelial carcinoma is a rare malignancy arising from the renal pelvis or ureter, accounting for 5-10% of urothelial carcinomas. Common clinical manifestations include hematuria and flank pain; however, many patients present with invasive disease at the time of diagnosis due to the absence of characteristic early symptoms. Fever may occur in association with infection or neoplastic fever, which can complicate the diagnostic process. Case presentation: A 47-year-old male with a history of recurrent nephrolithiasis and multiple prior right-sided urological interventions presented with persistent fever, right flank pain, and malaise. Despite broad-spectrum antibiotic therapy and nephrostomy drainage, there was no clinical improvement. Non-contrast computed tomography demonstrated obstructive nephrolithiasis with intraluminal gas within the right renal collecting system, raising suspicion of emphysematous pyelonephritis. Subsequent ultrasound showed similar findings with cortical thinning. Due to persistent sepsis and failure of conservative management, a right nephrectomy was performed. Histopathological examination revealed a high-grade urothelial carcinoma with extensive necrosis and local extension beyond the renal capsule. Immunohistochemistry showed positivity for alpha-methylacyl-CoA racemase, cytokeratin 7, and GATA-binding protein 3, with negative paired box gene 8 staining, confirming urothelial carcinoma. The patient was started on gemcitabine and cisplatin chemotherapy and remained clinically stable during approximately 3 months of follow-up. Conclusion: This case highlights a rare presentation of upper tract urothelial carcinoma mimicking emphysematous pyelonephritis, leading to a delayed diagnosis. Persistent or atypical upper urinary tract infections should raise suspicion for an underlying malignancy.