Pineal parenchymal tumor with marked retinoblastic differentiation: case report.

A 53-year-old woman was found to have a tumor in the pineal region. Histologically, Homer-Wright rosettes were sporadically distributed in a diffuse proliferation of round tumor cells that were immunoreactive for synaptophysin and chromogranin. A few perivascular pseudorosettes were also present, and the perivascular tumor cells were immunoreactive for glial fibrillary acidic protein and vimentin. By electron microscopy, well-developed junctions and pronounced interdigitation of abutting plasma membranes were noted in many tumor cells, as well as abundant intracytoplasmic microtubules. These findings indicated that the tumor was a pineal parenchymal tumor accompanied by an extraordinary epithelial-like differentiation, suggesting retinoblastic photoreceptor cell differentiation.