Astroblastoma

HyperdenseThere is a small heterogenous predominantly hyperdense mass in the right parietal lobe, with precessional hypodensity suggesting oedema. No calcifications were noted on non contrast CTbone window images (not shown).

MRI confirms a cortically-based right parietal massMass lesion predominantly T1 isointense to white matter, with focal hypointense areas. Adjacent white matter T1 hypointensity.

On T2 there are areas of marked hypointensity and small areas of hyperintensity, with marked vasogenic oedema. The lesion appears cortically based, and is heterogeneous on FLAIR, with foci of marked hypointensity.

The combination of a hyperdense lesion on CT and an avidly enhancing lesion on MRI is often seen in lymphoma, however, typically there is fairly marked diffusion restriction within the lesion, not seen here. The moderate edge restriction was not thought typical of lymphoma. The imaging appearance in conjunction with the prominent vasogenic oedema raised the possibility of a metastasis. Given the age of the patient metastatic melanoma was suggested in the differential. 

At histology, the morphology and immunophenotype were felt to be consistent with an astroblastoma. The histological features were considered low grade (no WHO grading currently exists for these lesions) with a favourable prognosis. Follow up 18 months post surgery shows no residual lesion. 

Astroblastoma is an uncommon glial neoplasm (0.45-2.8% brain gliomas) which is almost always supratentorial, occurring most commonly in young adults. The figure of 85% of lesions showing calcification on CT quoted in the literature is is based on a series of 7 patients. No overt calcification was seen on CT in this case, although the lesion was hyperdense. The lesion, in this case, was predominantly isointense, with heterogenous features in keeping with the reported solid and cystic components in this pathology.