Abstract

Congenital mesoblastic nephroma(CMN) is an important differential diagnosis of a renal mass occurring in the newborn or in early childhood. It was first described by Bolande as a separate disease entity distinct form Wilms' tumor. In 1974, Beckwith has predicted that this tumor has a pathologic spectrum with classic congenital mesoblastic nephroma at one extreme, unequivocally mallignant spindle cell sarcomas at the other, and intermediate "gray zone" lesions of indeterminate biologic significanse. In 1986, Joshi has described "atypical mesoblastic nephroma" as a potentially aggressive variant of CMN, which shows atypical gross and microscopic features such as hemorrhage, necrosis, high cellularity, and mitotic index. We report of a case of atypical mesoblastic nephroma presenting in a 38 days-old male infant. Grossly, the tumor involved the upper and midportion of the left kidney. On section, the cut surface was fleshy, grayish-white, and homogeneous. Microscopically, the tumorshowed high degree of cellularity and arrangement of fusiform cells in sheets and vague interlacing bundles. The individual tumor cells showed fusiform to oval nuclei, indistinct scanty pale-eosinophilic cytoplasm and many mitotic figures.

• Keywords: Kidney;congenital mesoblastic nephroma;Atypical mesoblastic nephroma;