Background: Primary neoplasms of the pineal gland are uncommon. Two patients with unusual primary pineal tumors that had similar distinctive histologic features are reported.
Methods: The surgically resected neoplastic pineal tissue from these patients were examined by light microscopy, immunohistochemistry, and electron microscopy and correlated with the patients' clinical course.
Results: These pineal tumors consisted of a mixture of spindle-shaped cells with fibrillated cell processes and many large lipidized and/or granular pleomorphic cells, some of which were multinucleated. These two tumors superficially resembled pleomorphic xanthoastrocytoma and granular cell tumors of the central nervous system. The pleomorphic tumor cells expressed glial fibrillary acidic protein and some also produced retinal S-antigen, a marker for retinal photoreceptor cells. Long-term follow-up (8 years) on one of these patients suggested a relatively "benign" clinical course.
Conclusions: It is possible that this newly described tumor may be a distinct subset of pineal gland neoplasias with a favorable biologic behavior despite the histologic features that would suggest otherwise.