The presence of a nephroblastoma, which is a neoplasm of the kidney that primarily affects children.
Comment:
Nephroblastoma is characterized by an abnormal proliferation of the metanephric blastema cells, which are believed to be primitive embryologic cells of the kidney. Clinically, nephroblastoma usually presents as an abdominal mass, and in some cases with abdominal pain, hypertension, hematuria, and fever.