Why is a horseshoe kidney particularly prone to developing calculi and pelviureteric junction obstruction?
- A The renal pelvis is extrarenal and the ureter has a high insertion, passing anteriorly over the isthmus, impairing drainage ✓
- B The isthmus compresses both renal veins, producing chronic venous congestion of the parenchyma
- C The abnormal position causes recurrent silent urinary infection that destroys the papillae
- D Both kidneys share a single common pelvis with a solitary ureter
Correct answer: A. The renal pelvis is extrarenal and the ureter has a high insertion, passing anteriorly over the isthmus, impairing drainage
Explanation
In horseshoe kidney the fused lower poles form an isthmus that lies anterior to the aorta, typically at L3, and the ureters must pass anteriorly over it. This high insertion and the anterior course create relative obstruction to pelviureteric drainage, stasis, and hence stones, infection, and PUJ obstruction. The isthmus lies anterior to the great vessels rather than compressing veins, drainage remains through two separate ureters, and the anomaly itself does not cause papillary destruction.
Reference: Gray's Anatomy for Students, 4th ed.
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