Persistent Unexplained Hydronephrosis in an Adolescent: A Multimodal Imaging Challenge.

Renal vein aneurysm (RVA) is an exceptionally rare vascular anomaly and an unusual cause of hydronephrosis. We report an asymptomatic 17-year-old male with persistent right hydronephrosis and preserved renal function. Serial ultrasonography demonstrated progressive pelvic dilatation, while repeat examination raised suspicion of an atypical extrapelvic component. Multimodal imaging, including ultrasonography, MAG3 scintigraphy, and computed tomography angiography, identified a right RVA, subsequently confirmed by laparoscopy and treated by aneurysmorrhaphy. Postoperative follow-up showed resolution of hydronephrosis. This case highlights the pivotal role of ultrasonography within a multimodal imaging approach for diagnosing rare vascular causes of persistent unexplained hydronephrosis.