Embryonal adenoma of the kidney: a report of two cases.

Embryonal (metanephric) adenoma of the kidney, like Wilms' tumor, exhibits small monomorphic, blue cells arranged as vague, tubular rosettes. Unlike Wilms' tumor, which requires chemotherapy or multi-modality therapy for optimal management, the available evidence indicates that embryonal adenoma is most likely cured by simple enucleation or nephrectomy. Two women, age 54 (Case 1) and 78 (Case 2), respectively, underwent needle biopsy for a radiologically well circumscribed renal lesion with associated hematuria. The cellular smears contained vague rosette-like arrangement of small, blue cells with scant cytoplasm and evenly distributed, fine, nuclear chromatin. In cell blocks, these cells were arranged as compact, primitive, tubular rosettes or rare, moresolid clusters. Assuming that the absence of undifferentiated blastema and primitive glomeruli represented a sampling error, a diagnosis suggesting of Wilms' tumor was made in Case 1. At nephrectomy, despite extensive sampling, the typical triphasic Wilms' morphology and anaplastic or necrotic areas were not seen. In the presence of architectural monotony, the diagnosis in Case 1 was amended to embryonal adenoma. Case 2 was cytologically diagnosed as embryonal adenoma of the kidney and is being followed conservatively. In our opinion, the presence of monotypic architecture at cytology/histology is very helpful in differentiating renal embryonal (metanephric) adenoma from Wilms' tumor.