Combined ultrasound and scintigraphic assessment of coexisting pelvic and cross-fused renal anomalies in a neonate: A case report.

Cross-fused renal ectopia and pelvic kidney are individually well-documented congenital anomalies, but their concurrent occurrence is exceedingly uncommon. We report a 2-day-old male neonate referred for postnatal evaluation after antenatal non-visualization of the left kidney. Initial ultrasound revealed a right kidney in normal position with mild hydronephrosis and a small left pelvic kidney with preserved corticomedullary differentiation. Follow-up imaging demonstrated right-sided cross-fused renal ectopia with 2 distinct moieties and mild hydronephrosis, while renal cortical scintigraphy confirmed near-symmetric split renal function. Differential diagnoses, including unilateral renal agenesis and duplex collecting system, were excluded based on imaging and functional studies. The patient required no intervention and continues under planned surveillance. This case highlights the importance of multimodal imaging in accurately characterizing rare and complex renal anomalies, guiding management, and avoiding unnecessary intervention.