BACKGROUND
Epidermoid cysts are benign, slow-growing lesions lined by keratinizing stratified squamous epithelium. Although they are among the most common cutaneous cysts, their occurrence within the urinary tract is exceptionally rare. In patients under oncologic surveillance, a new ureteral filling defect presents a significant diagnostic challenge, as benign lesions may closely mimic tumor recurrence and potentially lead to overtreatment or radical surgery.
CASE REPORT
We report the case of a 79-year-old man with a history of high-grade papillary urothelial carcinoma treated with transurethral resection of bladder tumor (TURBT), intravesical Bacillus Calmette-Guérin (BCG), chemotherapy, and immunotherapy. He remained in remission until a CT scan in 2026 showed a proximal right ureteral filling defect suspicious for recurrence. Given the high-risk oncologic context, malignancy was strongly suspected. Flexible ureteroscopy with complete endoscopic excision was performed. Histopathology demonstrated a keratinizing squamous-lined cyst with laminated keratin and no atypia. Immunohistochemistry confirmed a benign epidermoid cyst of urothelial origin, with no evidence of malignancy.
CONCLUSIONS
Ureteral epidermoid cysts are exceedingly rare benign lesions that can closely mimic urothelial carcinoma on imaging, particularly in patients with prior malignancy. This case highlights that imaging findings alone are insufficient for diagnosis in this context, and that definitive histopathological and immunohistochemical evaluation is essential. Accurate tissue diagnosis enabled minimally invasive management and avoided unnecessary radical surgical intervention. This diagnostic dilemma underscores the importance of considering benign etiologies in ureteral filling defects during oncologic surveillance.

Keywords: Case Reports; Dermoid Cyst; Ureter