Genitourinary Radiology > Embryology > Migration of the Kidney > Horseshoe Kidney

Horseshoe Kidney


Horseshoe kidney occurs in one of every 400 live births, making it the most common renal anomaly. Males are twice as likely to have the anomaly as females. It is a result of contact between and fusion of the developing metanephros. An isthmus develops between the two kidneys, consisting of a fibrotic band or functioning renal parenchyma. As fused kidneys ascend, the isthmus becomes hooked under the origin of the inferior mesenteric artery, resulting in a lower abdominal location and abnormal rotation, especially at the lower poles where the kidneys deviate medially. Associations include UPJ obstruction, duplication anomalies, and stone formation due to abnormal kidney geometry and urine stasis.

Contrast enhanced CT of abdomen and pelvis shows (1) medial orientation to the lower poles of both kidneys, (2 & 3) parenchymal isthmus (i) crossing midline and fusing underneath the inferior mesenteric artery (IMA) (arrow).

3D coronal reconstruction of the CT scan above showing the same findings. i = isthmus. Arrow = IMA.

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