Calyceal diverticulum masquerading as gross hydronephrosis: A diagnostic challenge

Calyceal diverticula are infrequent congenital anomalies of the renal collecting system that often serve as "radiological traps" due to their resemblance to hydronephrosis. This report details the case of a 38-year-old male whose. Initial ultrasonography demonstrated a large cystic lesion within the left renal sinus, raising suspicion for severe hydronephrosis. CT urography was subsequently performed to evaluate for obstructive uropathy. Delayed excretory phase imaging demonstrated contrast opacification within the lesion through a narrow communicating infundibulum, confirming the diagnosis of calyceal diverticulum. This case emphasizes that in the absence of an identifiable obstructive cause, delayed-phase imaging is mandatory to differentiate diverticula from obstructive uropathy, thereby preventing unnecessary surgical intervention.