Glioblastoma with signet-ring morphology: a case report and review of the literature.

Primary central nervous system tumors with signet-ring morphology are exceedingly rare. We report an unusual case of glioblastoma with signet-ring cell features in an 81-year-old woman. Microscopic examination revealed a highly anaplastic tumor, with a prominent proportion of tumor cells exhibiting signet-ring appearance characterized by classic round cytoplasmic inclusions and eccentrically positioned nuclei. The tumor cells were immunoreactive for glial fibrillary acidic protein and S100, and negative for cytokeratins, confirming their glial origin. Ultrastructurally, the tumor cells were noted to contain intermediate filaments, and by fluorescence in-situ hybridization analysis, they demonstrated intact 1p/19q. The presence of signet-ring cells in the central nervous system should immediately raise the suspicion of metastatic carcinoma, particularly from the upper gastrointestinal tract. In the present case, however, the morphological and immunohistochemical features were diagnostic of a malignant primary glial neoplasm (glioblastoma). This case highlights the diagnostic difficulties that can arise in such instances, given the rarity of signet-ring morphology in primary central nervous system tumors.