Pathology of Oligodendrogliomas 

Updated: Dec 17, 2019
  • Author: Roger E McLendon, MD; Chief Editor: Adekunle M Adesina, MD, PhD  more...
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Oligodendrogliomas are gliomas that arise in the cerebral hemispheres of young and middle-aged adults. The tumors have a propensity to arise in the gray matter or superficial white matter of the frontal lobes, but oligodendrogliomas may also arise in other regions of the central nervous system. These tumors have been demonstrated to have a frequent occurrence of loss of heterozygosity for the short arm of chromosome 1 and the long arm of chromosome 19 that, when present, are associated with a good chemotherapeutic responsiveness. Oligodendrogliomas also demonstrate a recurrent mutation in the 132 locus of the isocitrate dehydrogenase (IDH) gene resulting, most commonly, in an R132H mutation or, alternatively, in the IDH2 gene resulting in a R172K mutation. [1, 2]  The 1p,19q codeletions and the IDH mutations, when they co-occur in the same tumor, result in such a distinctive prognostic difference from other gliomas lacking in these mutations that the World Health Organization (WHO) has incorporated these molecular changes as signatures of specific types of oligodendrogliomas [3] :

  • Oligodendroglioma with IDH mutation and 1p,19q codeleltion (WHO Grade II) 
  • Oligodendroglioma, NOS (not otherwise specified) (WHO Grade II)
  • Anaplastic oligodendroglioma with IDH mutation and 1p,19q co-deletion (WHO Grade III)
  • Anaplastic oligodendroglioma, NOS (WHO Grade III)

The NOS designation is reserved for those tumors for which either complete molecular studies were not done or they were inconsistent with the histologic features.

These tumors are designated by the WHO as grade II tumors [3] ; however, oligodendrogliomas are prone to progress to WHO grade III and cause death. Occasionally a tumor may be encountered with an astrocytic component. Such cases, sharing both oligodendroglial and astrocytic features, are called oligoastrocytomas (see the following image).

Pathology of oligodendrogliomas. This tumor exhibi Pathology of oligodendrogliomas. This tumor exhibits oligodendroglial-type nuclei and scanty eosinophilic fibrillar cytoplasm amidst a mucinous background. Such tumors may be considered oligoastrocytomas.

Little is known of the cause(s) of oligodendrogliomas; no pattern of inheritance or familial risk for developing these tumors is known



Oligodendrogliomas represent approximately 5% of all gliomas, with an incidence of approximately 0.28 per 100,000. Data from the Central Brain Tumor Registry of the United States reflect a preponderance in white individuals and Hispanics relative to black individuals with a 3-to-1 ratio. [4] The tumor also exhibits a male-to-female ratio that ranges from 4:3 to 2:1. [5] The most frequently affected age groups are individuals in the fourth to fifth decades. [4]



Oligodendrogliomas preferentially arise in the cerebral hemispheres of young and middle-aged adults. Histologically, the tumors predominately affect the gray matter or superficial white matter of the frontal lobes. Although these tumors may also arise in other regions of the brain and spinal cord, the latter is rare.


Clinical Features and Imaging

Despite the variable prediagnostic time periods noted in some young adults with oligodendroglioma, the postoperative survival rates seem remarkably uniform, exhibiting survival rates of 75% at a 5 years, 46% at 10-years, and 17% at 15 years in one large study. [6] These rates compare favorably with the 81% 2-year survival rates from the Surveillance, Epidemiology, and End Results (SEER) data for all ages. [7]

More recent data seem to indicate better survivals, with a 10-year survival rate exceeding 50% for patients with either the well-differentiated or the anaplastic oligodendrogliomas. [8] However, age is a significant variable with respect to survival. Patients older than 65 years exhibit a significantly shorter survival rate than younger patients. [4] In addition to age, clinical features that are independent variables associated with survival include postoperative Karnofsky performance score, extent of surgical resection, and radiation therapy. [6, 9]

There are no specific laboratory tests that are helpful in making a diagnosis of oligodendroglioma in the absence of a biopsy.

The differential diagnosis of oligodendrogliomas includes the following:

  • Clear cell ependymoma
  • Extraventricular neurocytoma
  • Pilocytic astrocytoma
  • Small cell glioblastoma

Imaging Studies

Oligodendrogliomas at presentation are well-delineated, cortically based tumors that, less commonly, may have surrounding edema and may even erode the inner table of the skull. The computed tomography (CT) scan density of the neoplasms at presentation can be either low and attenuated or mixed, isodense, and hyperdense.

CT imaging is preferred over magnetic resonance imaging (MRI), as the MRI features are much more variable. The varieties of imaging include an isointense to hypointense mass on T1-weighted images (T1WI) and a somewhat hyperintense mass on T2-weighted images (T2WI); amorphous areas with dots of T1 hypointensity presumably related to cystic change; and a slightly hyperintense appearance on T2, which may progress to that of a honeycomb appearance (or the cysts may coalesce to form larger nonuniform cysts associated with a solid component resembling a mural nodule). [3]


Gross Findings

Grossly, the oligodendroglioma tumors are grayish pink, soft, but often well defined. On sectioning, oligodendrogliomas are seen to arise in the superficial aspects of the cerebral hemispheres, occasionally extending to the subarachnoid space as a creamy white mass resembling toothpaste to the operative surgeon. Occasionally, the tumor may arise in the deeper gray matter. The biological reason for the preference of the tumor to arise in the frontal lobe is unknown, but it is not restricted to this lobe.

Bilaterality is associated with crossing of the corpus callosum, and a tendency to spread by subarachnoid or subpial infiltration, in contrast to astrocytomas, in which the astrocytic tumor cells follow the parenchymal white matter tracts. Mucinous change is occasionally noted and may be so extensive as to confer a gelatinous appearance to the tumor.


Microscopic Findings

The oligodendroglioma derives its name from its close histologic resemblance to the benign oligodendroglial cell, with round, central nuclei and oval, water-clear cytoplasm (see the image below), which has been likened to the fried egg with its yolk.

Pathology of oligodendrogliomas. The classic appea Pathology of 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.

The tumor cells often form dense, hypercellular masses in the subcortical white matter, and they also have a propensity to aggregate around blood vessels and neurons ("satellitosis") in regions of cortical infiltration (see the following image).

Pathology of oligodendrogliomas. The cellular dens Pathology of oligodendrogliomas. The cellular density is moderate to high, and the fried-egg appearance dominates the histologic features.

Cortical infiltration may be associated with microcalcifications of blood vessels and neurons, which can sometimes be appreciated radiographically. It should be noted that astrocytomas may occasionally exhibit satellitosis. A concomitant loss of 1p and 19q is rare in cortical infiltrating oligodendrogliomas lacking satellitosis. [6]

Oligodendrogliomas are often associated with delicate arcuate vessels; however, this feature can also be encountered in ischemic cortex and may represent a reaction to tumoral ischemia rather than a nascent feature of the tumor itself. Another histologic feature commonly encountered is the formation of minigemistocytes, characterized by tumor cells with small eccentric droplets of eosinophilic cytoplasm about the size of the nucleus. These glial fibrillary acidic protein (GFAP)-immunoreactive cells have no prognostic significance. Rarely, the tumors may exhibit a focal granular eosinophilic change in the cytoplasm of some cells; such a change also has no diagnostic or prognostic utility.

Fresh cytologic smear preparations of oligodendrogliomas exhibit delicate vessels with small, round nuclei clinging to the vessels. The tumor cells also lack significant cytologic processes.

Occasionally, a tumor may be composed of a mixed population of round nuclei and elongated nuclei having fibrillar cytoplasm and exhibiting satellitosis, or it may demonstrate geographically separate and distinct regions of oligodendroglial and astrocytic (oval to elongated nuclei) morphology (see the following image). Such tumors are best classified as mixed oligoastrocytomas.

Pathology of oligodendrogliomas. This tumor exhibi Pathology of oligodendrogliomas. This tumor exhibits oligodendroglial-type nuclei and scanty eosinophilic fibrillar cytoplasm amidst a mucinous background. Such tumors may be considered oligoastrocytomas.




There are no specific antigenic markers for oligodendrogliomas that can be relied upon to make a diagnosis. However, the tumors are immunoreactive for S100 protein and microtubule-associated protein 2 (MAP2). The transcription factor Olig2, although expressed in oligodendrogliomas, remains nonspecific as an oligodendroglial marker. Alpha-internexin [10] and nogo-A [11] have been described as markers that appear to correlate with 1p/19 loss status. The 1p,19q co-deletion associated with an isocitrate dehydrogenase (IDH) gene mutation represents markers of good therapeutic response and are found in 80% of tumors with oligodendroglial morphology.



Approximately 80% of oligodendrogliomas exhibit a recurrent mutation in the isocitrate dehydrogenase (IDH) gene. This IDH mutation also is accompanied by allelic losses on the short arm of chromosome 1 and the long arm of 19q. These markers have been demonstrated to be of prognostic and theragnostic benefit in that tumors with loss of the full length of the short arm of chromosome 1 (ie, centromeric to telomeric loss) and long arm of chromosome 19 have been shown to be more responsive to chemotherapy and radiotherapy. The allelic losses (co-deletion events) are presumed to occur as somatic events during mitosis in tumors with unbalanced t(1;19)(q10;p10) translocation. [12]  Tumors lacking a concomitant IDH mutation very frequently exhibit a partial loss of 1p or 19q and do not fulfill the criteria for "Oligodendroglioma, IDH mutant and 1p,19q co-deleted" as defined by the World Health Organization. Oligodendrogliomas arising in children commonly do not exhibit these genetic markers.

Clues to the pathogenetic mechanisms driving oligodendroglioma on 1p and 19q have been provided by an exomic sequencing study of seven such tumors with these allelic losses. The study revealed six cases to exhibit somatic mutations in the CIC gene (homolog of the Drosophila gene capicua) on 19q and two tumors to exhibit somatic mutations in the the FUBP1 gene (encoding far-upstream element [FUSE] binding protein) on 1p. [13] The frequent losses affecting the CIC gene were subsequently supported by another study. [1]

Mutations in the promoter region of the TERT gene have also been described in oligodendrogliomas, IDH mutant and 1p,19q co-deleted, suggesting that a combined mutational approach to these genes may also help in the diagnosis of these tumors. [14]


Tumor Spread and Staging

Oligodendrogliomas are largely well circumscribed, but these tumors may occasionally be associated with local multilobar invasion/infiltration to present as gliomatosis cerebri. Distant spread via the cerebrospinal fluid (CSF) is unusual in most gliomas.


Prognosis and Predictive Factors

Oligodendrogliomas that are associated with a poorer survival include those tumors that exhibit necrosis, significant mitotic activity, and vascular proliferation (see the image below).  A single mitosis in a small biopsy is not sufficient evidence to justify a World Health Organization (WHO) Grade III designation.

Pathology of oligodendrogliomas. Oligodendroglioma Pathology of oligodendrogliomas. Oligodendrogliomas with vascular proliferation and significant mitotic activity are best considered to be anaplastic oligodendrogliomas (World Health Organization [WHO] grade III).

These tumors, while maintaining their round, uniform nuclear appearance, will very frequently exhibit scarlet cytoplasm (as shown in the following image), in contrast to the water-clear cytoplasm of the lower grade tumor. The clinical course of these more aggressive oligodendrogliomas is well recognized, and the tumors have been designated by the WHO as grade III. [3]

Pathology of oligodendrogliomas. Anaplastic oligod Pathology of oligodendrogliomas. Anaplastic oligodendrogliomas frequently take on eosinophilic cytoplasm and hyperchromasia of the nuclei. Such tumors may demonstrate necrosis among its diagnostic features.

The grading of mixed oligoastrocytomas is debatable, [2] but most pathologists rely upon the histologic features of the predominant element. Chromosomal studies for deletion of 1p and 19q may also be useful as such tumors frequently exhibit a loss of either 1p or 19q but not both. Therapeutic responsiveness seems to be dependent on the loss of the 1p36 locus. [15]

A controversy over the grade of oligoastrocytomas that exhibit vascular proliferation and necrosis has also arisen, with issues centered on whether the tumors should be designated as "anaplastic oligoastrocytomas grade IV" or "glioblastomas with oligodendroglial elements." [16] The WHO recommends thorough testing of these cases for 1p,19q co-deletion and IDH mutations to rule out an oligodendroglial histogenesis. Tumors lacking these markers are considered to be small cell glioblastomas that may also demonstrate EGFR amplification, ATRX loss, and p53 nuclear accumulation. The former term, glioblastomas with oligodendroglial elements, has been deleted from the most recent edition of the WHO. [3]