The CT appearance of Wilms tumor.

The computed tomographic (CT) findings in 30 Wilms tumors in 25 patients were reviewed and correlated with the pathological findings. Most tumors were quite large at the time of detection (average diameter 11 cm) and were cortical in origin. Peripheral lesions tended to grow exophytically. On the noncontrast studies an inhomogeneous mass with low-density areas (tumor necrosis) was seen. Small, focal calcifications (13.3%) and fat (6.9%) were much more readily identified with CT than with intravenous pyelography. After contrast medium injection, slight enhancement of the tumors was noted, and foci of necrosis became more prominent. A sharp demarcation between the tumor and normal parenchyma (seen in 19 cases) correlated with the pseudocapsule that is often present. Particularly striking was the presence of a persistent, ellipsoid area of increased attenuation corresponding to the compressed uninvolved renal parenchyma seen in 14 cases. Two cases were seen with complete tumor infiltration of the kidney pathologically and on CT. The primary clinical usefulness of CT in Wilms tumor is to detect multiple masses, to determine the extent of tumor, and to evaluate the opposite kidney.