Presentation
New onset of multiple generalised tonic-clonic seizures.
Patient Data
There is a lobulated hypodensity within the parasagittal right frontal lobe anteriorly measuring approximately 20 x 6 x 16 mm (AP x TR x CC). It is predominantly subcortical but also involves the overlying cortex. There is no calcification. The inner table of the adjacent frontal bone is scalloped and mildly thinned. The appearances are suspicious for an underlying parenchymal lesion.
The rest of the brain demonstrates normal grey-white matter differentiation. No acute haemorrhage. There is no mass effect or midline shift. The ventricles, surface CSF spaces, and basal cisterns are normal in appearance.
The abnormality seen on CT corresponds to a well-defined expansile, cortically-based lesion within the right superior frontal gyrus anteriorly measuring 18 x 11 x 17 mm (AP x TR x CC). There is mild cortical thickening and a subtle T1 hyperintense rim, and a larger area of T2/FLAIR hyperintensity involving the underlying white matter. There is no abnormal diffusion restriction, susceptibility artifact, or post-contrast enhancement. The lesion causes scalloping of the inner table of the adjacent skull, indicating that it is longstanding.
The remainder of the brain is normal.
Differentials include a diffuse glioma, cortically-based tumour (such as a DNET or ganglioglioma), or focal cortical dysplasia.
Case Discussion
An EEG showed multifocal right/midline frontal epileptiform discharges with occasional focal activity, which corresponds to the site of the lesion. The patient went on to have a resection. Intra-operatively, the lesion was noted to be soft and rubbery.
Histology
The sections of brain show an infiltrative tumour with a predominant component of interlacing bundles of spindle cells with elongated, pointed nuclei. There are some admixed larger cells with abundant eosinophilic cytoplasm. Mitoses are rare (up to 1 per 10 HPF) and there is no significant nuclear atypia. No necrosis is present. The tumour diffusely infiltrates cortex and reaches the cortical surface with a subpial palisading appearance. Oedematous areas are seen in the tumour, which do not stain with Alcian blue. Perivascular pseudorosette-like structures are seen.
Immunohistochemistry
Immunohistochemistry shows strong expression of GFAP, S-100 protein and vimentin antigens throughout the tumour. There is a dot-like cytoplasmic stain with EMA sometimes showing microlumina within the cells. There is no expression of pan keratin (Cam 5.2) antigens in the tumour cells. There are some ganglion-like cells which express synaptophysin, IDH-1, chromogranin A, S-100 protein, and NeuN antigens similar to cortical neurones consistent with entrapped neurones. The large cells with eosinophilic cytoplasm strongly express GFAP antigen. Ki67 varies from less than 1% to up to 5%. Mismatch repair immunoperoxidase stains (MLH1, PMS2, MSH2, and MSH6) are preserved.
Final diagnosis
Angiocentric glioma (WHO grade 1).
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