Mesoblastic nephroma is an important differential diagnosis of a renal mass occurring in the neonatal period or in early childhood. It is a rare monomorphous congenital renal neoplasm most commonly recognized during the first 3 months of life. With the widespread application of ultrasound imaging, many cases are recognized prior to birth. We report a case of mesoblastic nephroma detected by ultrasonograph at 36 weeks of intrauterine fetal life and removed after birth.
It showed a well circumscribed, grayish white, solid mass measuring 4x3x2 cm. The tumor was predominantly a classic type with a focal cellular pattern. Immunohistochemical and electron microscopic studies were done.
We reviewed 7 cases of congenital mesoblastic nephroma (4 cases of classical mesoblastic nephroma (CMN) and 3 cases of atypical mesoblastic nephroma (AMN)) using immuno-histochemical and flow cytometric study. Results are as follows. 1) The mean tumor size was 5 (3 to 7cm)cm in CMN and 9 (7 to 10cm)cm in AMN. The AMN revealed hemorrhage and necrosis in two Of three cases. A case of AMN showed cystic change without hemorrhage and necrosis. Mitotic count ranged in 0~4/10HPF in CMN and 20-35/10HPF in AMN. 2) Immunohistochemistry for vimentin was all positive. Actin, desmin were weakly positive in CMN, but negative in AMN. The findings were consistent with myofibroblastic differentiation in CMN and AMN was considered to be the less differentiated form of CMN. 3) Flow cytometiic analysis showed diploidy in two of two CMNs and two of three AMNs.
Only one AMN showed aneuploidy with DNA index of 1.41. %SG2M were 8.1 and 15.9 (mean 12.0) in CMN and 16.9, 32.9 and 19.3 (mean 22.9) in AMN, respectively. We concluded that AMN should be distinguished from CMN, clinicopathologically.
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.