Presentation
First seizure.
Patient Data
Large parenchymal calcification within the medial right parietal lobe deep white matter. Cingulate gyrus appers hypodense and expanded (best seen on coronal images).
No appreciable abnormal post contrast enhancement.
Abnormal high FLAIR signal in the right parietal lobe and cingulate gyrus medially with positive mass effect and cortical involvement, which extends anteriorly into the frontal lobe, and into the posterior limb of the internal capsule. The posterior body and splenium of the corpus callosum also appear to be involved, and high FLAIR signal abnormality crosses the midline.
Central in the FLAIR signal abnormality is a large area of susceptibility artifact with few adjacent punctate areas, shown to be calcification on the previous CT brain.
Wispy peripheral enhancement is most conspicuous at the posterior end of the cingulate gyrus.
MRS through the FLAIR signal abnormality demonstrates reversal of the Cho:Cr and depression of NAA peaks. Increased lipid/lactate peaks are also seen.
MR perfusion demonstrates mildly elevated CBV in the right parietal high FLAIR signal deep white matter.
Histology
MICROSCOPIC DESCRIPTION: The sections show features of a moderately cellular glial tumor. There is a proliferation of neoplastic oligodendroglial cells. They have round nuclei and perinuclear haloes. They extend into the cortex. Rare mitoses are seen, being 1 per 10 high-power fields. No microvascular proliferation or necrosis is present. The background shows a chicken-wire pattern of blood vessels and with scattered deposits of dystrophic calcification. The features are those of oligodendroglioma.
The tumor cells are focally p53 positive. The topoisomerase index is about 3-4%. IDH1-R132H immunostain is positive (mutated). MGMT is negative (likely methylated). ATRX shows no loss of staining (non-mutated).
DIAGNOSIS: Oligodendroglioma, IDH-mutant (WHO Grade II).
NB: ATRX status and 1p19q co-deletion status are usually inversely related. In this case, ATRX being intact suggests that 1p19q is co-deleted, further supporting the diagnosis, even in light of the 2016 WHO classification of CNS tumor update. Unfortunately, the classification goes out of its way to explicitly state that ATRX is not a replacement for 1p19q codeletion and as such strictly speaking, this tumor must be classified as an oligodendroglioma NOS.
Case Discussion
The signal abnormality centered in the right medial parietal lobe is most consistent with a glial tumor. The calcification on the CT brain indicates that an oligodendroglioma is the likely histological diagnosis. There are some features of a high-grade tumor, such as high CBV and enhancement, but these can also occur in low-grade oligodendrogliomas.
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