Incidentally detected crossed nonfused renal ectopia on contrast-enhanced trauma CT: A case report and review of the literature

Abstract

Crossed renal ectopia is a rare congenital anomaly in which a kidney is situated on the opposite side of the midline from its ureteral orifice in the bladder. The nonfused variant (type B) is an uncommon subtype, with a reported historical autopsy incidence of approximately 1 in 75,000, accounting for roughly 10% of crossed ectopias. Most cases are asymptomatic and diagnosed incidentally on imaging. A 35-year-old man with a previously documented right-sided duplex kidney underwent contrast-enhanced trauma computed tomography (CT) following an alleged assault. No acute traumatic injury was identified. CT of the abdomen and pelvis demonstrated a normally positioned right kidney in the right renal fossa alongside a second inferior reniform structure on the right side with normal enhancement and preserved corticomedullary differentiation, confirmed on portal venous phase axial and coronal multiplanar reconstructions. The left renal fossa was empty. The ureter of the ectopic kidney was traced crossing the midline, inserting orthotopically into the left side of the urinary bladder, with no parenchymal fusion between the 2 right-sided kidneys. These findings were diagnostic of crossed nonfused renal ectopia (McDonald and McClellan type B). Contrast-enhanced CT is central to the diagnosis and anatomical delineation of crossed nonfused renal ectopia, enabling characterization of renal position, ureteral course, and vascular anatomy. Recognition of this anomaly is critical to avoid misdiagnosis as renal agenesis and prevent inadvertent injury during surgical or interventional procedures. Clinicians and radiologists should maintain awareness of this rare entity and its associations with obstruction, nephrolithiasis, and malignancy.