GIANT-CELL EPENDYMOMA OF THE FILUM TERMINALE - A REPORT OF 2 CASES

We describe two histologically unusual cases of ependymoma of the filu m terminale. Both tumors occurred in 14-year-old boys. An intradural e ncapsulated mass attached to the filum terminale was demonstrated radi ologically in both cases and totally resected at surgery. In case I th e neoplasm was uniformly composed of pleomorphic giant cells and was w ithout perivascular pseudorosettes or myxopapillary changes. Case 2 wa s a myxopapillary ependymoma with multiple foci of pleomorphic gi ant cells. Neither tumor had prominent mitotic activity, necrosis, or endo thelial proliferation. Both tumors were immunopositive for cytokeratin and glial fibrillary acidic protein. Ultrastructural features include d basal laminae, interdigitating cell processes, microvilli, cilia, in tercellular junctions, and cytoplasmic intermediate filaments. Cytogen etic analysis in case 1 showed a hypodiploid karyotype with monosomy o f chromosomes 1, 10, 14, 16, 20, and 22, We interpret both tumors as m ost consistent with a variant of ependymoma. Because of the unique gig antocellular light microscopic appearance of the entire tumor in case 1, we propose classifying this tumor as a new morphologic subtype: gia nt cell ependymoma of the filum terminale. The combination of gigantoc ellular and myxopapillary features in case 2 supports a histogenetic r elationship between giant cell ependymoma and myxopapillary ependymoma .