A Missed Differential in an Extra-Axial Lesion with Calvarial Involvement

Extra-axial central nervous system lesions can occasionally involve the overlying calvarium. The involvement may be due to longstanding pressure effects or secondary to the aggressive behaviour of the lesion. The spectrum of such dural-based lesions varies from infectious/inflammatory to neoplastic etiology. We present a dural-based lesion with the erosion of the overlying calvarium in a young lady. In view of the short history with heterogenous enhancement on magnetic resonance imaging and bony erosion, hemangiopericytoma or malignant meningioma was suspected. The histopathology, however, proved it to be an anaplastic (grade III) ependymoma. Extra-axial ependymomas though uncommon have been reported. However, these extra-axial ependymomas presenting with calvarial erosion are unknown. The bony erosion, as in the present case, may suggest an aggressive tumour behaviour. The reported extra-axial supratentorial ependymomas along with their salient radiological/operative features are shortly reviewed. Also, the differentials of extra-axial lesions with calvarial involvement are touched upon.