GCTs account for approximately one-third of all pineal tumors and are histologically identical to gonadal GCTs. They predominate in men and usually occur in children and adolescents. Pineal GCTs occur almost exclusively in boys, but suprasellar tumors occur equally in boys and girls. GCTs fall into two major categories: germinomas and nongerminomatous (NGGCT) that include choriocarcinomas, embryonal cell carcinomas, teratocarcinomas, and endodermal sinus tumors. Benign, mature teratomas may also be seen.

Germinomas arise in the midline, usually in the pineal area and suprasellar cistern and occasionally in both areas simultaneously. Rarely do they develop in the cerebral hemispheres. Germinomas account for about half of all intracranial GCTs. They are histologically identical to the testicular seminoma and ovarian dysgerminoma. Germinomas are highly malignant; pathologically, they are frequently infiltrated by lymphocytes, which may occasionally confuse the diagnosis. Germinomas label with placental alkaline phosphatase; some contain syncytiotrophoblastic elements that produce β-human chorionic gonadotropin (β-hCG), which confers a slightly worse prognosis in some studies (Table 101.2). Germinomas may occasionally seed the cerebrospinal fluid (CSF).

NGGCTs are highly malignant and more aggressive than germinomas; they metastasize to the CSF more frequently than germinomas. Choriocarcinoma contains cyto- and syncytiotrophoblastic cells that produce β-hCG. Endodermal sinus tumors contain yolk sac elements that produce α-fetoprotein (AFP). High levels
of β-hCG or AFP in the CSF or serum indicate the presence of malignant germ cell elements. When markers are elevated, a tissue diagnosis is not necessary and patients are treated with radiation and chemotherapy.

All patients with histologically confirmed GCTs, regardless of subtype, should have serum and CSF tested for markers (if not done preoperatively), a complete spine magnetic resonance imaging (MRI) with gadolinium, and cytologic examination of CSF to complete staging prior to treatment.

Treatment first involves surgical resection to establish the diagnosis and debulk the tumor; if possible, gross total excision is the surgical goal. Patients with pure germinomas should be treated with radiotherapy, usually to 50.4 Gy; the port must include the whole ventricular system, and some radiotherapists treat the whole brain. If the tumor is disseminated in the CSF, craniospinal radiation is required. Chemotherapy may be useful at recurrence but is not recommended at diagnosis because most germinoma patients are cured with radiotherapy alone. NGGCTs require craniospinal radiotherapy and adjuvant chemotherapy in all cases after maximal resection. Benign GCTs such as teratomas, dermoids, and epidermoids are generally curable with surgery alone.

Primary pineal cell tumors are classified as low-grade pineocytomas (World Health Organization [WHO] grade I), pineal parenchymal tumors of intermediate differentiation (PPTID, WHO grade II or III), or the highly malignant pineoblastoma (WHO grade IV). Pineoblastomas are the same entity as primitive neuroectodermal tumors (PNET) of the pineal region. The higher grade tumors tend to occur in children and young adults, whereas pineocytomas usually occur in adults. Pineal tumors of all histologic grades may seed the leptomeninges, but pineocytomas do so only rarely. Complete resection of a pineocytoma does not require additional therapy, but incomplete resection should be followed by radiation. Intermediate-grade pineocytomas require radiotherapy, and pineoblastomas require neuraxis radiation and chemotherapy.

Gliomas account for one-third of pineal tumors. Most are invasive and have a prognosis comparable to astrocytomas of the upper brain stem. Some gliomas are low-grade, cystic, and may be surgically curable. Anaplastic astrocytomas and glioblastomas are less common. Oligodendrogliomas and ependymomas may also occur. Treatment of these tumors is identical to the treatment of gliomas in other areas of the central nervous system.

Meningiomas may arise from the velum interpositum or from the tentorial edge. They occur predominantly in middle-aged patients and in the elderly. They are amenable to surgical resection.

The pineal gland does not have a blood-brain barrier and, like the pituitary gland, may be underrecognized as a site of brain metastasis from systemic tumors. Miscellaneous tumors include sarcoma, hemangioblastoma, choroid plexus papilloma, lymphoma, and chemodectoma.

Benign cysts of the pineal gland are often found incidentally on imaging studies, and it is important to distinguish them from cystic tumors. They are normal variants of the pineal gland and consist of a cystic structure surrounded by normal pineal parenchymal tissue (Fig. 101.1). Radiographically, they are up to 2 cm in diameter and often have some degree of peripheral enhancement as a result of the compressed normal pineal gland. Pineal cysts may be found in 4% of all MRI scans. These cysts are static, anatomic variants and need no treatment unless they become symptomatic. The most common symptoms are headaches, followed by visual symptoms. The cysts may be sufficiently large to cause obstructive hydrocephalus. Decompression can occasionally be accomplished by third-ventricular endoscopic resection of the cyst.