Meningiomas are dural based extra-axial tumors and represent the most common tumor of the meninges. Originating from the meningocytes or arachnoid cap cells of the meninges, they are located anywhere that meninges are found. Although they usually easily diagnosed, and are typically benign with a low rate of recurrence following surgery, there are a large number of histological variants with variable imaging features and, in some instances, more aggressive biological behaviour. Meningiomas typically have an iso-intense signal compared to grey matter on both T1 and T2 weighted imaging and enhance vividly on both MRI and CT.
Meningiomas are more common in women, with a ratio of 2:1 intracranially and 4:1 in the spine. Atypical and malignant meningiomas are slightly more common in males. Meningeomas in patients under the age of 40 are rare and should raise suspicion of neurofibromatosis type 2 (NF2) when found in young patients.
Meningiomas are typically easily diagnosed, appearing as extra-axial masses with a broad dural base. Imaging is usually homogeneous and well circumscribed, although variants do occur.
T1: T1 imaging usually shows an isointense signal compared to grey matter (60-90%) or
hypointense to grey matter (10-40%).
T1 C+ (Gd): Meningiomas usually enhance intense and homogeneous on contrast imaging.
T2: Usually isointense to grey matter (~50%), or hyperintense to grey matter (35-40%).
DWI/ADC: atypical and malignant subtypes may show greater than expected restricted diffusion.