Wilms tumor in horseshoe kidneys: radiologic diagnosis

Two cases of nephroblastoma occurring in a horseshoe kidney are reported, and 32 cases from the literature are reviewed. The radiologic signs of horseshoe kidney may be difficult to evaluate with excretory urography when the mass is large. Rotational abnormalities of the opposite kidney that is not involved by tumor should suggest the possibility of an associated horseshoe kidney. Real-time ultrasonography and computed tomography are helpful in identifying the isthmus of the horseshoe kidney. Aortography confirms the presence of the horseshoe kidney and demonstrates the arterial supply to the isthmus and the tumor. Radionuclide scans demonstrate the isthmus when the tumor arises from an upper pole, but may not be diagnostic if the tumor arises from the isthmus.