Oligodendroglial Tumors

Oligodendroglioma (Grade 2)

This is a slowly growing, infiltrative tumor of adults, commonly situated in the cerebral hemispheres. It constitutes 5% to 10% of all gliomas. Seizures are often the presenting symptoms. Neurologic signs develop later in the course and indicate the location of the tumor. Average postoperative survival is 3 to 5 years, and recurrences are common.

Oligodendroglial tumors grades 2 and 3 that show a loss of chromosomal arms 1p and 19q respond favorably to radiation and chemotherapy, with survival reaching 10 to 15 years.

Grossly, oligodendroglioma is poorly demarcated, pinkish-gray in places gelatinous, and hemorrhagic. Gritty areas indicate calcifications, which are readily demonstrated on CT scan.

The histologic picture of a benign oligodendro-glioma is generally uniform, consisting of well-differentiated neoplastic oligodendrocytes with round or oval nuclei, scanty or no stainable cytoplasm (peri-nuclear halo-fixation artifact), and a prominent cellular membrane (honeycomb cells) (Fig. 11.18). A rich vascular supply of thin-walled capillaries separates the cells into small groups. A variable number of tumor cells immunoreact for GFAP. In some tumors, the cells are arranged in parallel rows resembling palisading, or they form pseudorosettes around blood vessels. Often, they spread along the leptomeninges. Calcifications are prominent. Microcystic and mucinous degenerations and hemorrhages may occur (Fig. 11.19).

Variants of oligodendrogliomas. Microgemistocytic oligodendroglioma displays small cells with round eosinophilic cytoplasm and eccentric nucleus. They immunoreact for GFAP (see Fig. 11.19). Anaplastic oligodendroglioma (grade 3) is distinguished by increased cellularity, nuclear pleomorphism, mitotic activity, vascular proliferation, hemorrhages, and micronecroses. Leptomeningeal spread, subarachnoid dissemination, and metastasis outside the nervous system also occur.

Oligoastrocytoma contains well-differentiated neo-plastic astrocytes and oligodendrocytes either diffusely intermingled or separated.

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