Pediatric idiopathic retroperitoneal fibrosis.

Retroperitoneal fibrosis (RPF) is a very rare disease that is even more rare in the pediatric population. Even less common are idiopathic pediatric cases of retroperitoneal fibrosis, with a majority of reported pediatric retroperitoneal fibrosis cases being associated with secondary etiologies. We present an 11-year-old Caucasian female that was diagnosed with idiopathic retroperitoneal fibrosis using magnetic resonance imaging (MRI) to work-up severe bilateral hydronephrosis that was identified with retroperitoneal ultrasound. Given the uncommon nature of this serious condition, we present this case to illustrate the importance for physicians to include retroperitoneal fibrosis in the differential diagnosis of a pediatric patient presenting with obstructive urinary findings and understand the utility of using MRI to diagnosis and monitor this disease.