A pineal region tumor is an abnormal growth in or near the pineal gland. Depending on the type of tumor, surgery may involve a craniotomy to remove it.
The pineal gland, a tiny, pinecone-shaped area located in the midline of the brain behind the third ventricle, synthesizes and secretes the neurotransmitters melatonin, which plays the critical role of regulating the body’s circadian rhythm, and serotonin, a precursor to melatonin. Other functions of the pineal gland remain incompletely understood. This gland is composed of a variety of cells, such as glial cells, endothelial cells, sympathetic nerve cells, pineal parenchymal cells and germ cells. Given the diversity of cells, a wide variety of tumor types can arise in this region.
Germ cell tumors
Germ cell tumors develop from germ cells, which normally reside in the gonads and eventually become eggs or sperm. Most germ cell tumors are found in the gonads, but rarely—in about 2 to 3 percent of cases—these tumors arise outside of the gonads, most commonly in the brain. The reason for this is that during embryonic development, some germ cells accidently become trapped inside the developing brain, where they later develop into a tumor.
Intracranial germ cell tumors, which make up about one-third of pineal region tumors, are classified as germinomas and nongerminomatous, according to the World Health Organization. Germinomas are highly malignant and make up about half of intracranial germ cell tumors. Nongerminomatous tend to be malignant and more aggressive than germinomas and are further classified as choriocarcinomas, embryonal cell carcinomas, endodermal sinus tumors, mixed germ cell tumors and teratomas. Teratomas are broken down into immature teratomas, mature teratomas and teratomas with malignant transformation.
Pineal cell tumors
Unlike germ cell tumors, which arise in the pineal region despite being unrelated to the pineal gland itself, pineal cell tumors arise directly from the functional cells of the gland, pineal parenchymal cells, which are specialized nerve cells involved in processing visual stimuli. Pineal cell tumors are divided into pineocytoma, pineoblastoma and mixed pineal tumors. Pineocytomas are generally slow-growing and benign, whereas pineoblastomas are aggressive and malignant. Mixed pineal tumors are a combination of pineocytoma and pineoblastoma.
Gliomas, namely astrocytomas and oligodendrogliomas, arise from glial cells and account for about one-third of pineal region tumors. For information about gliomas, please click here.
Meningiomas in this region arise from arachnoid cells. For information about meningiomas, please click here.
Other tumors, such as gangliogliomas and hemangioblastomas, can arise in this region, but constitute only a small portion of pineal region tumors.
Dermoid and epidermoid cysts are slow-growing sacs filled with material; they are not true tumors because they do not arise from brain tissue. Similar to germ cell tumors, these cysts are the result of cells being trapped in the brain during embryonic development. They are present at birth.
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