Pleomorphic pineocytoma with extensive neuronal differentiation: report of two cases.

Two pineal parenchymal tumors are presented, arising in a 54-year-old man and a 72-year-old woman; respectively. They showed isomorphic, cellular areas of small cells, often with characteristic pineocytomatous rosettes, and of medium-sized cells, as well as less cellular regions with highly pleomorphic, often ganglioid large cells. Immunohistochemistry disclosed extensive neuronal differentiation. There was intense positivity for neurofilament protein and microtubule-associated protein 2 in the pleomorphic areas and more variable expression in the isomorphic regions. Diffuse synaptophysin positivity was seen, accentuated along the borders of pleomorphic cells and in the rosettes, as well as diffuse interstitial and/or cytoplasmic expression of neuron-specific enolase, PGP 9.5 and tau. beta-Tubulin III was detected in most cells and slight positivity was found in the rosettes. Expression of glial fibrillary acidic protein, however, was restricted to resident astrocytes and an interstitial network of processes. These neuronally differentiated pleomorphic pineocytomas underline the broad histomorphological spectrum of pineal parenchymal tumors.