Oligodendroglioma with signet-ring cell morphology: a case report with an immunohistochemical and ultrastructural...

A case of oligodendroglioma with signet-ring cell (SRC) morphology arising in the right thalamic region in a 12-year-old boy is described. Histopathologically, the tumor was a composite neoplasm consisting of typical oligodendroglioma and anaplastic components with aggregates of SRC. Immunohistochemically the SRC were negative for glial fibrillary acidic protein (GFAP) but surrounded by GFAP-positive anaplastic cells with high-grade nuclear features. Typical oligodendrogliomatous components were negative for GFAP. The Ki-67 labeling index evaluated with MIB-1 antibody was 1.3% in the SRC component, 9.2% in the GFAP-positive anaplastic cell component, and 0.8% in the typical oligodendrogliomatous component. Ultrastructurally, the cytoplasm of the SRC was filled with irregularly and widely dilated cisternae of rough endoplasmic reticulum containing granular material. Intermediate filaments and a small number of other organelles were distributed in the perinuclear and peripheral areas. Both the SRC and anaplastic cells had slender cytoplasmic processes, although those of the SRC were short and few in number. These findings are distinct from those of SRC hitherto described in oligodendrogliomas to date, and suggest that there is a morphological heterogeneity in SRC rarely seen in oligodendrogliomas and that some examples of SRC are related to the anaplastic cells with astrocytic features in their origin.