Oligodendrogliomas are a type of glioma that are believed to originate from the oligodendrocytes of the brain or from a glial precursor cell. They occur primarily in adults (9.4% of all primary brain and central nervous system tumors) but are also found in children (4% of all primary brain tumors). Signs and symptoms
Oligodendroglioma arise mainly in the frontal lobe and in 50–80% of cases, the first symptom is the onset of seizure activity, without having any symptoms beforehand. Headaches combined with increased intracranial pressure are also a common symptom of oligodendroglioma. Depending on the location of the tumor, many different neurological deficits can be induced, including, but not limited to, visual loss, motor weakness and cognitive decline. A computed tomography (CT) or magnetic resonance imaging (MRI) scan is necessary to characterize tumor size, location, and hetero- or homogeneity. Final diagnosis relies on biopsy and histopathologic examination of the tumor mass. Cause
The cause of oligodendrogliomas is unknown. Some studies have linked oligodendroglioma with a viral cause. A 2009 Oxford Neurosymposium study illustrated a 69% correlation between NJDS gene mutation and the tumor initiation. A single case report has linked oligodendroglioma to irradiation of pituitary adenoma. Diagnosis
Microscopic appearance
Oligodendrogliomas cannot currently be differentiated from other brain lesions solely by their clinical or radiographic appearance. As such, a brain biopsy is the only method of definitive diagnosis. Oligodendrogliomas recapitulate the appearance of the normal resident oligodendroglia of the brain. (Their name derives from the Greek roots oligo meaning " few" and dendro meaning "trees".)
They are generally composed of cells with small to slightly enlarged round nuclei with dark, compact nuclei and a small amount of eosinophilic cytoplasm. They are often referred to as "fried egg" cells due to their histologic appearance. They appear as a monotonous population of mildly enlarged round cells infiltrating normal brain parenchyma and producing vague nodules. Although the tumor may appear to be vaguely circumscribed, it is by definition a diffusely infiltrating tumor.Classically they tend to have a vasculature of finely branching capillaries that may take on a "chicken wire" appearance. When invading grey matter structures such as cortex, the neoplastic oligodendrocytes tend to cluster around neurons exhibiting a phenomenon referred to as "perineuronal satellitosis". Oligodendrogliomas may invade preferentially around vessels or under the pial surface of the brain.Oligodendrogliomas must be differentiated from the more common astrocytoma. Non-classical variants and combined tumors of both oligodendroglioma and astrocytoma differentiation are seen, making this distinction controversial between different neuropathology groups. Molecular diagnostics may make this differentiation obsolete in the future. Other glial and glioneuronal tumors with which they are often confused due to their monotonous round cell appearance include pilocytic astrocytoma, central neurocytoma, the so-called dysembryoplastic neuroepithelial tumor, or occasionally ependymoma. Histopathological grading
The histopathologic grading of oligodendrogliomas is controversial. Currently, the most commonly used grading schema is based on the year 2007 World Health Organization (WHO) guidelines. An updated classification is in progress. Oligodendrogliomas are generally dichotomized into grade II (low grade) tumor. Unfortunately, the WHO guidelines include subjective criteria in grade II.