The Cytological Differentiating Potential of Pineal Parenchymal Neoplasms (True Pinealomas)

A series of 28 pineal parenchymal tumours is described, with special reference to the potential of some of these neoplasms to differentiate along glial or ganglionic lines, or both. The more undifferentiated tumours (pineoblastomas, 11 cases) were the most frequent: they are histologically similar to medulloblastomas. One example showed focal differentiation to retinoblastoma at the primary site. The histological features of pineoblastomas merged with those of pineocytomas (7 cases), in which the lobular architecture is reminiscent of that of the mature pineal gland. In addition, 10 further examples in the group of pineocytomas showed more advanced differentiation as follows: towards astrocytes only (2 cases), towards ganglion cells only (1) case) and towards both astrocytes and ganglion cells (gangliogliomas) (7 cases). Confirmation of the pineal parenchymal nature of these neoplasms and of their differentiating potential was provided by a modification of the Achúcarro-Hortega's silver carbonate impregnation technique for pineal parenchymal cells, by specific silver impregnations for axonal processes, and by an immunoperoxidase stain for glial fibrillary acidic (GFA) protein. Electron microscopy of one new example of pineocytoma with neuronal and astrocytic differentiation demonstrated the presence of numerous microtubules, of clear-centred and dense-core vesicles, and of synaptic complexes. Seven illustrative clinical histories with pathological findings are presented. The identification of special features of cellular differentiation is of importance in evaluating the biological behaviour of these neoplasms since a definite correlation can be established between the patient's age, some of the cytological variants, and the malignant potential of the tumour. Pineoblastomas are highly malignant neoplasms of children and young adults which disseminate widely throughout the cerebrospinal fluid pathways. -ineocytomas without cellular evidence of further differentiation occur at any age and are also clinically malignant, but with a somewhat lesser tendency to metastasize than pineoblastomas. Pineobytomas with astrocytic differentiation occur in adults and may be either slowly growing or malignant. Pineocytomas with neuronal or with neuronal and astrocytic differentiation occur in later life, remain localized, and are relatively benign. Since the latter account for approximately one-third of pineal parenchymal tumours and are likely to be relatively radio-resistant, tissue diagnosis is imperative for a determination of the therapeutic approach. Radiation to the entire neuraxis should be administered to patients with pineoblastomas and malignant pineocytomas in view of their high frequency of cerebrospinal metastasis. An accurate histological classification of these tumours therefore carries important clinical and therapeutic implications...