Pineal parenchymal tumor of intermediate differentiation with cytologic pleomorphism.

We report a case of pineal parenchymal tumor in a 33-year-old man incidentally detected by radiological examination. The MRI showed an unhomogeneously enhanced, small tumor (approximately 1 cm in size) in the pineal region. A tumor specimen was obtained at endoscopic biopsy. Routine histology showed a highly cellular tumor characterized by a predominance of small cells showing high nuclear : cytoplasmic ratio and moderate nuclear atypia, pleomorphism including giant cells and an absence of pineocytomatous rosettes. Mitotic figures were rare (approximately 1 per 10 high-power fields). Tumor necrosis was not evident. Immunohistochemically, the neoplastic cells showed positivity for neural markers (neurofilament protein, synaptophysin) and pinealocyte-associated antibodies (PP1, PP5, PP6), but not for glial fibrillary acidic protein or S-100. The MIB-1 labeling index was relatively high (6.3%). Ultrastructurally, there was some evidence of pinealocytic differentiation, such as vesicle-crowned rodlets (synaptic ribbons) and paired twisted filaments in neoplastic cells. Thus, the tumor was confirmed as a pineal parenchymal tumor of intermediate differentiation by histology, immunohistochemistry and electron microscopy. This case indicates that marked cytologic pleomorphism can occur in pineal parenchymal tumors of intermediate differentiation.