Case report: diminished density surrounding a meningioma, verified to be an overlying cystic astrocytoma.

Meningiomas examined by computed tomography (CT) often show an area of decreased density surrounding the tumor. Various explanations include edema of the adjacent brain, loculated or trapped subarachnoid fluid, widening of the subarachnoid space, tissue necrosis, and demyelination. The present report describes a case in which this zone of diminished density was a large cystic astrocytoma, overlying a subfrontal meningioma.