Massive unilateral non-functioning hydronephrosis in horseshoe kidney.

The occurrence of non-function in one half of a horseshoe kidney resulting from hydronephrosis can, if unrecognized, create a serious surgical as well as medical problem. The anterior position of the ureter in relation to the isthmus, as well as strictures and accessory vessels increase the incidence of hydronephrosis, which if severe enough, can go on to non-function. The key diagnostic factor is the observation of the visualised side, which shows the characteristic malrotation of the calyces and the deviation of the long axis of the kidneys; these are associated with a mass effect on the obstructed side, with or without a 'crescent' sign. Five cases of this unusual occurrence are presented.