Supernumerary kidney incidentally detected on staging CT scan: A rare case report

Supernumerary kidneys are rare congenital anomalies arising from abnormal renal development, with fewer than 100 cases documented in the literature. A 55-year-old male presented with chronic nonbloody diarrhea and was diagnosed with a locally advanced rectal tumor. A staging CT scan incidentally revealed a right-sided supernumerary kidney measuring 4.5 cm, alongside a larger right kidney (7.3 cm) and a normal left kidney (10.2 cm), with independent arterial supply and normal excretory function. While this finding did not impact the patient's oncological treatment plan, awareness of such anomalies is essential for surgical planning to avoid complications. This case underscores the importance of recognizing supernumerary kidneys to guide clinical decision-making in oncological and urological interventions.