Primary Leptomeningeal Oligodendroglioma, IDH-Mutant, 1p/19q-Codeleted

Abstract

We present a case of a 43-year-old woman with a history of headaches and blurry vision. Ophthalmologic examination identified papilledema. MR imaging demonstrated a right parietal region mass with patchy areas of contrast enhancement and focal calcifications. Intraoperative examination and exploration revealed an extra-axial mass with no apparent parenchymal involvement. Microscopic examination revealed solid sheets of tumor cells with clear cell cytologic features and no discernable intra-parenchymal tumor component. Molecular studies demonstrated the presence of IDH1 IDH1 c.395G>A p.R132H and CIC c.601C>T p.R281W mutations and 1p/19q codeletion. The radiographic features, gross appearance, and microscopic and molecular characteristics of the mass support the diagnosis of primary leptomeningeal oligodendroglioma, IDH-mutant, 1p/19-codeleted. This case represents one of a very few reported instances of molecularly-defined solitary, primary, intracranial oligodendroglioma, without definitive involvement of the brain parenchyma.

Keywords: 1p/19q-codeletion; ATRX; CIC; FUBP1; IDH1; diffuse glioma; leptomeningeal oligodendroglioma.

Figure 1

Radiologic findings. Axial T2-weighted FLAIR imaging (A) demonstrates an extra-axial hyperintense mass centered within the right paramedian parietal region with a focus that appears to be inseparable from the adjacent cortex (asterisk in A,B). On the axial T1 post contrast images (B,C) the lesion is predominantly nonenhancing and hypointense, with areas of heterogeneous enhancement (arrow in B). Also noted is lateral displacement of a cortical vessel (arrow in C), suggestive of an extra-axial location of the mass. Coronal non-contrast CT imaging demonstrates a focus of coarse calcification (arrow in D) in the hypoattenuating mass.

Figure 2

Histologic findings. (A) Microscopic examination showed diffuse sheets of a tumor composed of relatively small cells with round-to-oval nuclei and scant-to-cleared cytoplasm. (B) GFAP was positive in a subset of tumor cells. (C) IDH1 p.R132H mutant protein immunohistochemistry was strongly positive. (D) ATRX protein wildtype expression was retained. (E) Weak expression of p53 protein. (F) Low Ki67 labeling index of 4.8%. (G) Mitotic activity (arrow) was quantified at a maximum of 2 per 10 high-power fields using phosphohistone H3 (pHH3) immunostaining.