A. An axial contrast-enhanced CT image of a 5-year-old child with a palpable flank mass demonstrates a large, somewhat heterogeneous renal mass. The lesion is hypoattenuating relative to the enhancing renal parenchyma anterior and medial to the mass. Thinned parenchyma envelops the margin of the mass (arrows), helping to confirm a renal origin, that is, the "claw sign." B. The remaining renal tissue is along the superior medial aspect of the neoplasm, as visualized on this coronal CT image. The tumor has a heterogeneous enhancement pattern and there are poorly enhancing central areas of necrosis. Despite the large size of this tumor, the margins are well defined and there is no vascular encasement.