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Oligodendroglioma


KEY FACTS

Terminology

  • Well-differentiated, slowly growing but diffusely infiltrating cortical/subcortical tumor

Imaging

  • Most common site is frontal lobe (50-65%)

  • Best diagnostic clue: Partially calcified subcortical/cortical frontal mass in middle-aged adult

    • Typically T2 heterogeneous, hyperintense mass

  • ~ 50% enhance

    • Heterogeneous enhancement is typical

  • New enhancement in previously nonenhancing oligodendroglioma suggests malignant progression

Top Differential Diagnoses

  • Anaplastic oligodendroglioma

  • Low-grade diffuse astrocytoma

  • Ganglioglioma

  • Dysembryoplastic neuroepithelial tumor

  • Pleomorphic xanthoastrocytoma

  • Cerebritis

  • Cerebral ischemia

Pathology

  • Loss of heterozygosity for 1p and 19q (50-70%)

  • WHO grade II

  • Anaplastic oligodendroglioma = WHO grade III

  • Oligodendrogliomas carry better prognosis than astrocytomas of same grade

Clinical Issues

  • 5-10% of primary intracranial neoplasms

  • Seizures, headaches, and focal neurologic deficits are most common presentations

  • Peak incidence: 4th and 5th decades

  • Median survival time = 10 years

  • 1p, 19q deletions and IDH1 (+) associated with more favorable prognosis

Axial graphic shows a heterogeneous cystic and solid mass involving the cortex and subcortical white matter, typical of oligodendroglioma. Note the deep infiltrative margin
and calvarial remodeling
.

Axial NECT in a 20-year-old man shows a large, calcified, left frontal lobe mass
, typical of oligodendroglioma. The vast majority (70-90%) of oligodendrogliomas show calcification. The calcification helps distinguish this tumor from other gliomas, particularly astrocytomas.

Axial FLAIR MR in the same patient shows a heterogeneous, hyperintense infiltrative mass expanding the frontal gyri
. The frontal lobe location and involvement of both cortex and subcortical white matter are typical of oligodendroglioma.

Axial T1WI C+ MR in the same patient shows heterogeneous enhancement
in this grade II oligodendroglioma. Differentiating a grade II from a grade III oligodendroglioma is difficult on conventional imaging. MRS and MR perfusion may help predict the tumor grade preoperatively.

TERMINOLOGY

Definitions

  • Well-differentiated, slowly growing, but diffusely infiltrating, cortical/subcortical tumor

IMAGING

General Features

  • Best diagnostic clue

    • Partially calcified subcortical/cortical mass in middle-aged adults

  • Location

    • Typically involves subcortical white matter (WM) and cortex

    • Majority supratentorial (85%), hemispheric WM

      • –

        Most common site is frontal lobe (50-65%)

      • –

        May involve temporal, parietal, or occipital lobes

      • –

        Rare: Posterior fossa

      • –

        Extremely rare: Intraventricular, brainstem, spinal cord, primary leptomeningeal

  • Size

    • Variable

  • Morphology

    • Infiltrative mass that appears well demarcated

CT Findings

  • NECT

    • Mixed density (hypo-/isodense) hemispheric mass that extends to cortex

    • Majority calcify, nodular or clumped Ca++ (70-90%)

    • Cystic degeneration common (20%)

    • Hemorrhage, edema are uncommon

    • May expand, remodel, erode calvaria

  • CECT

    • ~ 50% enhance

    • Enhancement varies from none to striking

MR Findings

  • T1WI

    • Hemispheric mass, hypo- to isointense to gray matter

    • Typically heterogeneous

    • Cortical and subcortical with cortical expansion

    • May appear well circumscribed with minimal associated edema

  • T2WI

    • Typically heterogeneous, hyperintense mass

      • –

        Heterogeneity related to Ca++, cystic change, less commonly blood products

    • May appear well circumscribed with minimal associated edema

    • Typically expands overlying cortex

    • Hemorrhage, necrosis are rare unless anaplastic

    • May expand, erode calvaria

  • FLAIR

    • Typically heterogeneous, hyperintense

    • Typically expands overlying cortex

    • May appear well circumscribed but infiltrative

  • T2* GRE

    • Ca++ seen as areas of “blooming”

  • DWI

    • No diffusion restriction is typical

  • T1WI C+

    • Heterogeneous enhancement is typical

    • ~ 50% enhance

    • Rarely, leptomeningeal enhancement is seen

  • MRS

    • ↑ Cho, ↓ NAA

    • Absence of lipid/lactate peak helps differentiate from anaplastic oligodendroglioma

    • 2HG MRS has been found helpful to identify IDH status

  • Perfusion MR

    • Relative cerebral blood volume (rCBV) can help differentiate grade II from grade III

    • Foci of elevated rCBV can mimic high-grade tumor

  • SWI: Shows Ca++ as hypointense foci

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