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PINEAL PARENCHYMAL TUMORS

Pineal parenchymal tumors arise from pineocytes or their precursors, and they are distinct from other pineal gland neoplasms such as astrocytic and germ cell tumors.

PINEOCYTOMA (WHO grade II) is a slow-growing pineal parenchymal neoplasm that primarily occurs in young adults.[40] Pineocytomas account for fewer than 1% of all brain tumors and comprise approximately 45% of all pineal parenchymal tumors. Adults aged 25 to 35 years are most frequently affected. No specific cytogenetic abnormalities or molecular genetics exist with this tumor. The 5-year survival rate has been reported to be as high as 86%.

PINEOBLASTOMA (WHO grade IV) is a highly malignant primitive embryonal tumor of the pineal gland that manifests primarily in children.[41] Pineoblastomas are rare brain tumors that comprise approximately 45% of all pineal parenchymal tumors. No specific cytogenetic abnormalities or molecular genetics exist with this tumor. Tumors similar to pineoblastomas in appearance have been observed in patients with familial (bilateral) retinoblastoma. Projected 1-, 3-, and 5-year survival rates of pineoblastoma patients treated by various modalities are 88%, 78%, and 58%, respectively.

PINEAL PARENCHYMAL TUMORS OF INTERMEDIATE DIFFERENTIATION are monomorphous tumors exhibiting moderately high cellularity, mild nuclear atypia, occasional mitosis, and the absence of large pineocytomatous rosettes.[40] They comprise approximately 10% of all pineal parenchymal tumors and occur in all age groups. No specific cytogenetic abnormalities or molecular genetics exist with this tumor. Clinical behavior is variable.

(Refer to the Pineal Parenchymal Tumors section of this summary for treatment information. Refer to the PDQ summary on Childhood Central Nervous System Embryonal Tumors Treatment for more information.)

MENINGEAL TUMORS

Many tumor types are found in the meninges. Most common are meningiomas, which arise from meningothelial cells. Many mesenchymal, nonmeningothelial tumors also occur, but most are rare in the meninges and more commonly found at other sites; only hemangiopericytomas are mentioned here because they are more frequent and historically confused with meningiomas. A wide spectrum of melanocytic lesions can also be found; these are rarely hemangioblastomas and are classified as of uncertain histogenesis.

MENINGIOMAS (WHO grades I-III) are typically slow-growing, benign, WHO grade I tumors attached to the dura mater and composed of neoplastic meningothelial (arachnoidal) cells.[42] Meningiomas are estimated to comprise between 13% and 26% of primary brain tumors and have an annual incidence of approximately 6 per 100,000 persons. Meningiomas usually occur in adults, with a peak occurrence during the sixth and seventh decades of life. Women are affected more often than men, with a female to male ratio as high as 2:1. ATYPICAL MENINGIOMAS (WHO grade II) constitute 4.7% to 7.2% of meningiomas, while ANAPLASTIC (MALIGNANT) MENINGIOMAS (WHO grade III) account for 1.0% to 2.8% of meningiomas. These higher grade meningiomas may show a conspicuous predominance in males. Most meningiomas arise within the intracranial, orbital, and intravertebral cavities. Spinal meningiomas are most common in the thoracic region; atypical and anaplastic meningiomas are more common on the falx and the lateral convexities.