Background
Oligodendrogliomas (ODs) are primary glial brain tumors that are divided into grade II and anaplastic grade III tumors (World Health Organization [WHO] criteria). Typically, they have an indolent course, and patients may survive for many years after symptom onset. Their good prognosis relative to other parenchymal tumors probably stems from inherently less aggressive biological behavior and a favorable response to chemotherapy, a recently discovered finding based on genetic characteristics.
Pathophysiology
Oligodendrogliomas arise in the cerebral hemispheres and are distributed among the frontal, parietal, temporal, and occipital lobe, in approximately a 3:2:2:1 ratio. Rarely, they can arise in the cerebellum, brain stem, and spinal cord. [1] They usually occur in the cerebral white matter and are very cellular, with uniform nuclei. They react with glial fibrillary acidic protein on immunostaining.
Epidemiology
Frequency
The incidence of oligodendrogliomas ranges from 5–19% of all intracranial tumors. The newer studies showed incidence of oligodendrogliomas to be around 25% of all gliomas. This may be explained by the improvements in the treatment of oligodendrogliomas, prompting neuropathologists to favor the diagnosis.
Mortality/Morbidity
The morbidity and mortality profile for oligodendrogliomas is much better than for astrocytic tumors. However, it also depends on tumor location and pressure effects, as with any other intracranial lesion. The median survival from initial diagnosis of all low-grade oligodendrogliomas (LGOs) is 4–10 years, but it is only 3–4 years for anaplastic oligodendrogliomas.
Demographics
Oligodendrogliomas occur in both sexes, with a male-to-female predominance of 2:1.
Oligodendrogliomas may be diagnosed at any age but occur most commonly in young and middle-aged adults, with a median age at diagnosis of 40–50 years. In children, only 6% of gliomas are diagnosed as oligodendrogliomas.
Prognosis
Combined loss of 1p/19q is a significant predictor of overall survival in anaplastic oligodendroglioma and is also significantly associated with longer recurrence-free survival and chemosensitivity. [2]
The phosphatase and tensin homologue deleted by chromosome 10 (PTEN) alteration is associated with a poor prognosis.
Other variables, including age of the patient at time of diagnosis, location and extent of surgical resection, postoperative performance status, histologic features of the tumor, and use of adjuvant therapies and early presentation with seizures, determine the prognosis for an individual patient. Overall, as many as three fourths of patients with nonanaplastic tumors can be expected to survive 5 years from the time of diagnosis, with a median reported survival duration of 6-10 years. For those with anaplastic oligodendrogliomas, median survival is more likely to be 3–4 years. Late progression of disease is common, so the usual 5-year survival time used to indicate "cure" in other cancers is not relevant for oligodendrogliomas.
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Classic histologic image of oligodendroglioma. This image shows monomorphous tumoral proliferation that consists of round, regular cells with a small, central, hyperchromatic nucleus surrounded by clear cytoplasm. Few calcifications are present.
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Smear preparation of anaplastic oligodendroglioma. This image reveals increased nuclear pleomorphism and vascular proliferation.
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Contrast-enhanced computed tomography scan in a 44-year-old man with a 3-year history of epileptic seizures. This image reveals a calcified hypoattenuating lesion that is invading the corpus callosum.
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Computed tomography scan of a low-grade oligodendroglioma. This image reveals a well-demarcated, left frontal hypoattenuating lesion with a small calcification.
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Sagittal gadolinium-enhanced T1-weighted magnetic resonance image of a low-grade oligodendroglioma. This image demonstrates no contrast enhancement.
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Oligodendrogliomas. This tumor exhibits oligodendroglial-type nuclei and scanty eosinophilic fibrillar cytoplasm amidst a mucinous background. Such tumors may be considered oligoastrocytomas.
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Oligodendrogliomas. The classic appearance of the oligodendroglioma is that of a round to oval, water-clear cytoplasm ringing about round to lobulated nuclei. The chromatin appearance is finely threadlike to smudgy, often associated with pointlike basophilic chromocenters, rather than nucleoli.
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Oligodendrogliomas. The cellular density is moderate to high, and the fried-egg appearance dominates the histologic features.
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Oligodendrogliomas. Oligodendrogliomas with vascular proliferation and significant mitotic activity are best considered to be anaplastic oligodendrogliomas (World Health Organization [WHO] grade III).
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Oligodendrogliomas. Anaplastic oligodendrogliomas frequently take on eosinophilic cytoplasm and hyperchromasia of the nuclei. Such tumors may demonstrate necrosis among its diagnostic features.
