Background
Oligodendrogliomas are primary glial brain tumors that are divided into grade 2 and grade 3 tumors, with grade 3 tumors showing anaplastic features such as microvascular proliferation, necrosis, and increased mitotic rate; distinction between the two grades can be pathologically difficult. Oligodendrogliomas are molecularly defined by the presence of complete deletion of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q) (1p/19q co-deletion). Virtually all oligodendrogliomas also have a mutation in isocitrate dehydrogenase (IDH1 or IDH2). 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 radiation and chemotherapy.
Pathophysiology
Oligodendrogliomas arise in the cerebral hemispheres and have a predilection for the frontal lobes. They can rarely arise infratentorially or in the spinal cord. Leptomeningeal spread can occur rarely in late stages of the disease. Oligodendrogliomas have a “fried egg” appearance under the microscope with sheets of round nuclei surrounded by clear cytoplasm.
Epidemiology
Frequency
The incidence of oligodendrogliomas is around 5% of all central nervous system neuroepithelial tumors. [1] . About 1,000 oligodendrogliomas are diagnosed per year in the United States.
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 between 25 and 45 years old. Grade 3 tumors have a median age at diagnosis that is 5–10 years older than grade 2 tumors.
Prognosis
Prior to the WHO 2016 classification of CNS tumors, grades 2 and 3 gliomas were not molecularly distinguished by 1p/19q codeletion status. The median survival of all low-grade gliomas was estimated at 4–10 years, and survival of grade 3 gliomas was estimated at 3–4 years after diagnosis. Recently, 1p/19q codeletion was independently validated as a favorable prognostic factor in low grade glioma.{ref35. Another factor that increases probability of survival in low-grade gliomas is a high performance status. [2]
Patients with low-grade gliomas can be conventionally stratified into “high risk” and “low risk” categories, with risk referring to risk of tumor progression or recurrence. “Low-risk” patients have a better prognosis than “high-risk” patients. “High-risk” patients are defined as age older than 40 years, or less than a gross total resection achieved at surgery; “low-risk” patients are those who are both younger than age 40 and underwent gross total resection of the tumor. “Low-risk” patients might defer treatment with radiation and chemotherapy and followed with surveillance only, while “high-risk” patients may benefit with upfront adjuvant treatment. [3] This risk classification may change in the future as our understanding of the contributions of genetic markers to survivability evolves.
Progression-free and overall survival of low grade gliomas in “high-risk” patients was studied in the RTOG-9802 trial. The trial compared outcomes in patients who received radiation therapy alone versus radiation therapy (RT) plus chemotherapy with procarbazine, CCNU, and vincristine (PCV). Progression-free and overall survival at 12 years were significantly increased in the RT+PCV group. The median overall survival was 13.3 years in the RT+PCV group versus 7.8 years in the RT alone group, and progression-free survival at 10 years was 51% in the RT+PCV group versus 21% in the RT alone group. In a subgroup analysis, oligodendroglioma diagnosis was a favorable prognostic factor resulting in increased overall and progression-free survival; however, oligodendrogliomas were classified histologically in this study, not by 1p/19q status. [4]
Patient Education
Throughout the entire process, educate the patient and family through regular follow-up care and involvement of support groups to cope with physical, emotional, and spiritual stress. With proper education, the patient and family can develop good insight into the course and prognosis of the tumor.
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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.
