A malrotated kidney with a complete duplicated collecting system develops in-utero. Before you are born, kidneys go through a complicated series of developmental steps where they change orientation and position. Malrotation occurs when these steps do not occur in the normal way and end up in an abnormal orientation, position, or even both. However, a duplicated collecting system, or duplex collecting system, is one of the most common congenital renal tract abnormalities. It can be characterized by an incomplete fusion of the upper and lower pole resulting in a variety of complete or incomplete duplications of the collecting system.
