Patients with Wilms’ tumors most frequently present with which of the following?

e. A unifocal, unilateral lesion

It is currently hypothesized that Wilms’ tumor arises from primitive metanephric blastema and individual tumors often contain not only primitive metanephric cells but also cartilage, skeletal muscle and squamous epithelium. Most tumors arise unifocally within the kidney but approximately seven percent of unilateral Wilms’ tumors are multicentric. The proportion of synchronous bilateral tumors among all nephroblastoma patients ranges from 4.4 to 7.0% while that of metachronous tumors is 1.0–1.9%. Wilms’ tumors are equally distributed with regard to the left and right side and may occur with no apparent connection to the kidneys. Usually, extrarenal Wilms’ tumor occurs in the retroperitoneal area but other reported sites include pelvis, scrotum and inguinal region.