Vanishing contrast enhancement in malignant glioma after corticosteroid treatment.

Malignant gliomas of the brain typically exhibit on CT or MRI a strong peripheral contrast enhancement area with a variable central zone of necrosis. These tumours are not known to change their radiological appearance and contrast enhancement pattern under systemic steroid treatment--a feature usually associated with primary CNS lymphoma. We report two cases of adult patients with glioblastoma multiforme and atypical hemispherical contrast enhancement initially demonstrated on MRI or CT, which disappeared after dexamethasone administration. At the same time, however, another tumour focus became visible, in both cases localised in the corpus callosum. Histological diagnosis was confirmed by stereotactic biopsy in both cases. This unusual changing pattern of contrast enhancement seems to be associated with multifocal malignant glioma with partial blood-brain barrier disruption modified by dexamethasone, and may present diagnostic difficulties in respect to neuroimaging and selection of target areas for tumour biopsy.