We describe the occurrence of a renal tumor in a 7-month-old female infant. The lesion was entirely composed of spindle cells, similar to fibroblasts or smooth muscle cells. On purely cytologic criteria, this case was indistinguishable from the “cellular variants” of congenital mesoblastic nephroma, a lesion heretofore not known to be capable of distant spread. However, a pulmonary metastasis developed 3 months after surgery, and again after chemotherapy and radiotherapy. Unlike most benign mesenchymal renal tumors of infancy, our case was detected clinically past the age of 3 months; another distinguishing feature was the presence of multiple foci of necrosis. Dense cellularity and high mitotic rate were further characteristics that could portend an untoward outcome. These findings support the concept of a spectrum of histopathologic changes within the group of exclusively mesenchymal renal tumors of infancy. The benign, well-differentiated, congenital lesions occupy one end of the spectrum. Our findings firmly establish that definitely sarcomatous lesions occupy the other end; that these can manifest early in infancy, before 1 year of age; and that histopathologic examination is of crucial value in assessing the prognosis.
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González‐Crussi et al. (1980) studied this question.