Disorder of the ascent of the kidneys or ectopic kidneys
A kidney is ectopic when, without ptosis, it does not lie in the lumbar fossa. The ectopia is the result of an incomplete or missing ascent. It can occur in the upper or lower region (pelvic kidney) or even crossed.
A high ectopia is an extremely seldom anomaly and usually affects the left kidney in men.
A true ectopia must be distinguished from an ascent of a normal kidney into the thorax region due to an agenesia of the diaphragm. An ectopia can also be the result of a posttraumatic ptosis.
A true intrathoracic ectopia is supplied by a renal artery that arises from the aorta thoracalis. For its part, the renal vein discharges into the vena cava superior. The diagnosis is made using urography.
A deep ectopia is most often encountered in the pelvis (but also in the lumbar or iliac regions), and can be the cause of a dystocia (difficult labor) for the woman. Constrictions of the pyelo-ureteral transition are also frequently seen.
In a crossed ectopia a kidney migrates to the other side. Its ureter crosses the midline and inserts normally into the bladder. The crossed ectopia can occur unilaterally or bilaterally. In the case of a unilateral crossed ectopia a fusion of the two kidneys often occurs. Ectopias are normally asymptomatic.
Its incidence is around 1/600. It is assumed that it arises due to a joining of both kidneys from both sides and during the 5th week (stage 15) when both organs still lie very close together in the small pelvis.
The two kidneys are most often bound together at the lower pole. The ureters that go downwards from the horseshoe kidneys are not abnormal. The horseshoe kidney, though, lies further down than normal ones do. The further ascent is impeded by the inferior mesenteric artery that arises in the lower region of the abdominal aorta.
A horseshoe kidney is normally asymptomatic or has only unspecific clinical signs: e.g., urinary tract infections and lithiasis (stone formation). However, they also occur in the more complex malformation syndromes or together with a chromosome aberration (, ). In children with horseshoe kidneys the Wilms' tumor appears 2-8 times more frequently than in normals.