Congenital anomaly in which kidneys are fused at their lower poles in midline

Kidneys on opposite sides with lower poles fused in midline

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  Note that in crossed-fused ectopia, both kidneys are located on one side

Presence of isthmus is defining feature; isthmus may be fibrous or functioning renal tissue

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  Isthmus crosses midline anterior to spine and aorta but posterior to inferior mesenteric artery

Cross-sectional imaging (CT or MR) to define vascular anatomy and can be used to visualize associated complications such as malignancy

May be first detected by ultrasound but vascular anatomy better defined by CTA or MRA

Arterial supply and venous drainage may be complex

Crossed-fused ectopia

Renal ectopia

Paraaortic lymphadenopathy/retroperitoneal mass

Fusion of kidney precursors in early gestation when still located in pelvis, preventing appropriate ascent

1 in 500 children; M:F = 2:1

30% asymptomatic

Up to 2/3 have associated abnormalities (most commonly genitourinary)

Complications include uretero-pelvic junction obstruction, infection, nephrolithiasis

Increased risk of malignancy such as Wilms tumor, urothelial carcinoma, and carcinoid

Prognosis is good in absence of associated abnormalities

Suspect when lower renal poles disappear medially

Look for isthmus in midline anterior to aorta and posterior to inferior mesenteric artery

Use compression to displace bowel