Developmental anomalies of the Renal system

Mesenchymal tissue in the embryo, that will form the kidneys, eventually joins with a tubular outpouching of that part of the cloaca, which forms the bladder. As the embryo grows, each connection lengthens and divides within the kidney to become (respectively) the ureter and pelvicalyceal system. Duplication of parts may occur or the tissue may migrate to another location. Separation or division of tissue may also fail. Horseshoe kidney or two kidneys on the same side, crossed ectopia of the kidneys, can be seen below.

The site of insertion (origin) of the ureter influences its function, usually by the intramural length. Reflux occurs, if the intramural portion of the ureter is too short, and ureteric obstruction may result, if the intramural portion is too long and dilates to form a ureterocoele. A longer intramural path in the bladder or an ectopic insertion for the ureter is more common in situations where the kidney is not in its normal position (ectopic kidney or upper moiety of a duplex kidney), but reflux is more frequent in the lower moiety of a duplex kidney.

Teaching point: The presence of an obvious anomaly does not, of itself, exclude another, more dangerous, pathology. The statistical risk of disease in association with anomalies is the same as for normals with the same environmental exposure.