Pineocytoma with neuronal differentiation--case report.

The authors describe a case of pineocytoma studied by light and electron microscopy and the immunoperoxidase method. The tumor consisted of two types of cells bearing either chromatin-rich or pale nuclei. These cells were arranged in rosettes and contained pale, eosinophilic material at the center, or in lobular patterns with thin connective tissue and a few blood vessels. Bodian silver staining disclosed a delicate tangle of argyrophilic fibers and processes with small, club-like terminations. These findings are characteristic of pineocytoma. On ultrastructural examination, the tumor cells were found to be closely packed, in clumps separated by numerous fine or expanded, interlacing processes, some of which contained microtubules. A few dense core vesicles and clusters of clear vesicles similar to synaptic vesicles were seen, the latter being aggregated around desmosome-like thickenings in the cellular membrane, suggestive of a synaptic complex. Some tumor cells were positive for neuron-specific enolase and S-100 protein. Only a few cells positive for glial fibrillary acidic protein were distributed in the tumor tissue, but it was not ascertained if they were tumor cells or normal, pre-existing astrocytes. The tumor was diagnosed as a pineocytoma with neuronal differentiation.