History
In prior years, a long delay occurred between symptom onset and diagnosis (as long as 29 y in some series). Because of earlier and better imaging availability, oligodendrogliomas have been diagnosed much earlier in recent years.
Like other intracranial space-occupying lesions, oligodendrogliomas present with focal cerebral dysfunction, depending on location, and rarely as increased intracranial pressure.
Most oligodendrogliomas present as a single lesion in the cerebral hemispheres. Typically, they are cortical or subcortical; they rarely are found in deep gray structures, and occasionally they may be primarily intraventricular. Rarely, they can occur infratentorially or in the spinal cord. Occasionally they may be multifocal, like other gliomas.
The most common presenting symptom is seizure, observed at diagnosis in as many as half of patients. As many as 80% of patients have seizures at some time during their illness. Depending on the location of the tumor, the seizure can be simple partial, complex partial, or generalized. Previously undiagnosed oligodendrogliomas may be identified with medically refractory epilepsy.
Occasionally patients with oligodendrogliomas are brought to medical attention for headache, symptoms of increased intracranial pressure, or focal neurological deficits.
Tumors that arise within the ventricles may cause obstructive hydrocephalus and are more likely to disseminate through the cerebrospinal fluid (CSF). Rarely, they can metastasize outside the nervous system, especially the anaplastic oligodendroglioma.
In long-surviving patients with 1p/19q co-deletion, indolent leptomeningeal disease may be a complication of oligodendroglioma, which may have implications for the treatment. [3, 4]
Occasional patients present with strokelike transient ischemic attacks or with intracerebral hemorrhage.
Physical
Physical findings depend on the location of the tumor.
Frontal, parietal, and temporal lobe tumors most commonly present with seizures. Seizures may be simple, complex partial, and even generalized. Frontoparietal tumors may present with hemiparesis and sensory neglect. Sensory neglect is pronounced in right hemispheric lesions. Temporal lobe tumors rarely may present with visual field defects, although patients may be unaware of hemianopsia.
Rare intraventricular oligodendroglioma may present with signs and symptoms of increased intracranial pressure such as headache, visual disturbance, and papilledema.
Posterior fossa oligodendrogliomas are uncommon. However, well-documented cases are described in children and may present with cerebellar ataxia and increased intracranial pressure.
Causes
No causes or risk factors are known. Occasional clustering occurs in some families, although the mode of inheritance is unknown. Patients with anaplastic oligodendrogliomas who have loss of heterozygosity on 1p or combined loss of heterozygosity on 1p and 19q survive substantially longer (mean, 10 y) than patients whose tumors lack these genetic changes (mean, 2 y).
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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.
