Urothelial mucosal malformation: a rare cause for ureteropelvic junction obstruction.

Ureteropelvic junction obstruction (UPJO) constitutes a significant cause of morbidity in children and exists in a wide range of severity and clinical manifestations. The cause of UPJO remains largely unknown except for a small group, in which crossing vessels have been considered etiological. Herein we describe a unique case in which intraluminal occlusion was the result of mucosal malformation, characterized by invaginated and branching urothelial epithelium present in the lamina propria. We believe that the present case is the first such description of this type of alteration.