An immunohistochemical and electron microscopic study of atypical teratoid/rhabdoid tumor.

We report two infant cases with atypical teratoid/rhabdoid tumor (AT/RT) located in the cerebellar vermis and spinal cord. MRI showed the tumors were isointense on T1-weighted images and mixed intensity of isointense and slight high intensity on T2-weighted images. Postcontrast MRI demonstrated clear margin of tumor and heterogeneous strong enhancement. It was difficult to differentiate the tumor from medulloblastoma by hematoxylin and eosin staining. However, immunohistochemical staining showed that these tumor cells react positively for cytokeratin, smooth muscle actin (SMA), and epithelial membrane antigen (EMA) and helped us with the differentiation. Electron microscopic study has confirmed the presence of mesenchymal components, such as filaments and desmosome junctions in the rhabdoid cells, but no neuronal components. The tumors rapidly increased in size, showing high MIB-1 index, and the prognosis was gave.