Unusual cerebellar ganglioglioma with marked cytologic atypia.

Neuronal differentiation is well documented in cerebellar primitive neuroectodermal tumors but is uncommon in other cerebellar neoplasms. Although rare, gangliogliomas and gangliocytomas have been previously described in the cerebellum. We report a cerebellar ganglioglioma in a 14-year-old boy, which revealed bizzare markedly pleomorphic cells with extremely pronounced nuclear atypia but less than one mitosis per 50 high-power fields and no necrosis. The tumor showed glial as well as neuronal differentiation, with abundant bi- and multinucleated ganglion cells. There were abundant Rosenthal fibers, eosinophilic granular bodies, focal calcification, and perivascular lymphocytic infiltrates. There has been no evidence of tumor recurrence or neurological deterioration 21 years after surgery, although the narked nuclear atypia led to an initial diagnosis of an anaplastic glioma. We stress the need for careful evaluation of cerebellar gliomas in children that show only nuclear atypia or endothelial hyperplasia in the absence of other features of malignant.