Calyceal Diverticulum: A Cystic Lesion Mimicking a Urinary Tract Infection.

Calyceal diverticulum (CD) is an uncommon renal anomaly in children and often mimics other cystic lesions, making diagnosis challenging. We report the case of a nine-year-old boy evaluated during follow-up after an episode of acute pyelonephritis. He remained asymptomatic, with normal examination findings and appropriate growth. Renal ultrasound revealed a non-vascularized cystic lesion with heterogeneous content in the upper pole of the right kidney. Subsequent magnetic resonance imaging demonstrated communication with the collecting system, confirming the diagnosis of CD. While typically asymptomatic, CD may initially present with complications such as urinary tract infection (UTI). Identification relies on imaging modalities capable of visualizing the diverticular communication with the calyceal system. Management in pediatric patients is generally conservative, with surgical intervention reserved for recurrent infection, abscess formation, persistent pain, gross hematuria, or progressive enlargement. This case highlights that UTI is a complication of calyceal diverticulum and could be its first clinical manifestation. It further emphasizes the importance of including CD in the differential diagnosis of atypical pediatric renal cystic lesions and reinforces the crucial role of advanced imaging in establishing a definitive diagnosis.