Clinical Overview:  Meningioma is the most common extraaxial brain tumor. They represent 20% of all primary brain tumors. They are most common in adults and are usually asymptomatic. They can arise in a radiation field many years after irradiation.

As in this case, 5% are atypical and 1% are malignant, having a much worse prognosis.

 
CT:  They are sharply circumscribed and lobulated mass that abuts the dura. The are extraaxial thus forming an obtuse angle to the dura. This is a key observation in making the diagnosis because they are the most common extraaxial brain mass. Furethermore, the obtuse angle to the dura can be associated with a "dural tail" sign which is highly suggestive of a meningioma differentiating it from other extraaxial mass like a schwannoma (figure 1). On unenhanced CT, most of the time they are denser than brain. 20% have calcifications. It enhances very brightly and occasionally have a non-enhancing necrotic center. The amount of surrounding edema varies. There is hyperostotic or osteolytic bony reaction in 20% of the cases. CT can be 95% sensitive with contrast and 85% without contrast.

MRI:  Finding are characteristic of extraaxial masses: 1. CSF/vascular cleft betweeen the mass and brain (figure 1) 2. displacement of gray-white matter interface around mass.

T1 - iso or slightly hypointense relative to cortex

Angio:  Angiography demontrastes tumor blush that comes early and stays late which is has been called the "mother-in-law sign." Angiography is useful for preoperative embolization to decrease tumor vascularity. Also some cavernous hemangioma and capillary hemangiomas can look identical to a meningioma