The pineal germinoma has its origin in germinal cells and is therefore classified separately from tumors that arise in pineal cells (pineocytoma and pineoblastoma). It is a firm, discrete mass that usually reaches 3 to 4 cm in greatest diameter. It compresses the superior colliculi and sometimes the superior surface of the cerebellum and narrows the aqueduct of Sylvius. Often it extends anteriorly into the third ventricle and may then compress the hypothalamus. A germinoma may also arise in the suprasellar area. Microscopically, these tumors are composed of large, spherical epithelial cells separated by a network of reticular connective tissue and containing many lymphocytes.
The pineocytoma, atypical pineocytoma, and pineoblastoma reproduce the normal structure of the pineal gland. These tumors enlarge the gland, are locally invasive, and may extend into the third ventricle and seed along the neuraxis. Cytologically, the pineocytoma is a moderately cellular tumor with none of the histologic attributes of anaplasia. The tumor cells tend to form circular arrangements, so-called pineocytomatous rosettes. Pinealocytes may be impregnated by silver carbonate methods, and some contain the retinal S antigen of photoreceptor cells. Pineoblastomas are highly cellular and composed of small, undifferentiated cells bearing some resemblance to medulloblasts.
Teratoma and dermoid and epidermoid cysts of the pineal body have no special features—some are quite benign. Gliomas of the pineal have the usual morphologic characteristics of an astrocytoma of varying degrees of malignancy. In some cases, the clinical syndrome of the several types of pineal tumors consists solely of symptoms and signs of increased intracranial pressure. Beyond this, the most characteristic localizing signs are an inability to look upward and slightly dilated pupils that react on accommodation but not to light (Parinaud syndrome). Sometimes ataxia of the limbs, choreic movements, or spastic weakness appears in the later stages of the illness. It is uncertain whether the ocular and motor signs are caused by neoplastic compression of the brachia conjunctivae and other tegmental structures of the upper midbrain or to hydrocephalus (dilatation of the posterior part of the third ventricle). Probably both mechanisms are operative.
Precocious puberty occurs in males who harbor a germinoma. Although the pineal gland is the source of melatonin, sleep is not affected to any important degree in patients with these tumors, as discussed in “The Pineal Gland and Melatonin” in Chap. 26. Measurement of CSF or serum melatonin is useful mainly in the detection of tumor recurrence after surgical extirpation. In patients with a germ cell tumor, the CSF or serum may show elevations of beta-human choriogonadotropin or alpha-fetoprotein. The diagnosis is made by neuroimaging (Fig. 30-15). The CSF may contain tumor cells and lymphocytes but may also be entirely normal.
Treatment Pineal lesions were formerly judged to be inoperable. However, the use of the operating microscope now makes it possible to excise them by a supracerebellar or transtentorial approach. Operation for purposes of excision and histologic diagnosis is advised because each type of pineal tumor must be managed differently. Moreover, one may occasionally find an arachnoidal cyst that needs only excision. The germ cell tumors should be removed insofar as possible and the ventricular region radiated for germinomas, and the whole neuraxis is treated in the case of nongerminomatous lesions. The use of chemotherapy in addition to or instead of cranial irradiation is still being evaluated. Several of our patients have survived more than 5 years after the removal of a pineal glioma.
Neuroepithelial Tumors (DNET), Germinomas, Gangliocytomas, Mixed Neuronal-Glial Tumors, and Lhermitte-Duclos Disease