Importance of re-examination for medulloblastoma and atypical teratoid/rhabdoid tumor.

Medulloblastoma may can be difficult to distinguish from atypical teratoid/rhabdoid tumor (AT/RT), since they resemble each other histologically. We re-examined whether AT/RT was included among cases who had been diagnosed as medulloblastoma. All of fifteen medulloblastomas (10 males and 5 females) diagnosed at the Kitasato University Hospital were collected and stained immunohistochemically. Two cases originally diagnosed as medulloblastoma were reclassified as AT/RT based on histological re-examination including immunohistochemical studies. While these two cases of AT/RT were found during infancy, only one medulloblastoma was found in infancy.Histologically, small rhabdoid cells and large, pale, bland cells were common but typical rhabdoid cells were not seen in the two AT/RTs. Gland-like structures were also seen. The tumor cells in AT/RT, but not those in medulloblastoma, were immunoreactive for vimentin, epithelial membrane antigen and smooth muscle actin. In conclusion, if a diagnosis of medulloblastoma is made histologically, it should be confirmed immunohistologically, since it is difficult to distinguish AT/RT from medulloblastoma. When appropriate treatment was specifically targeted at AT/RT it may improve the outcome.