Expansion
The kidney ascends from the pelvis to the lumbar region, and a fused lower pole is caught by the inferior mesenteric artery
Expansion
The definitive kidney (metanephros) forms in the pelvis and ascends to the lumbar region between weeks 6 and 9, partly by differential growth of the body. As it ascends it acquires successive arterial supplies from the aorta, the lower ones regressing.
Anomalies follow directly:
- Horseshoe kidney - the lower poles fuse across the midline; ascent stops when the isthmus catches on the inferior mesenteric artery at L3. Present in about 1 in 500; associated with Turner syndrome, and with pelviureteric junction obstruction, stones and infection
- Pelvic (ectopic) kidney - ascent fails entirely
- Accessory renal arteries - persistence of the lower arterial supplies; present in about 25 per cent
The kidney also rotates 90 degrees medially during ascent, which is why the hilum faces medially rather than anteriorly.