Meningiomas

4 Meningiomas

After glioblastomas, meningiomas are the second most common primary brain tumor, and the most common extraaxial tumor. They occur most commonly in females with risk factors including ionizing radiation, head trauma, and likely high exposure to estrogen and progesterone. Meningiomas are most commonly located over the cerebral convexity adjoining the mid or anterior one third of the superior sagittal sinus, but may occur, in decreasing order of frequency: along the lateral convexity, the sphenoid ridge, olfactory groove, suprasellar parasellar region, and in the posterior fossa.

Meningiomas may be relatively difficult to visualize on nonenhanced MRI as they tend to be relatively isointense to brain on T1WI, T2WI, and FLAIR (Fig. 4.1A). The presence of surrounding edema, demonstrating increased SI on T2WI and decreased SI on T1WI, may aid in lesion recognition on unenhanced scans. Approximately half of meningiomas, however, do not demonstrate significant associated edema (Fig. 4.1A). Thus, contrast administration (as in Fig. 4.1B) greatly aids in the detection of these lesions. Due to their lack of a BBB, meningiomas demonstrate prominent (and typically homogeneous) enhancement—a finding useful for lesion identification, characterization, and distinguishing surrounding edema (Fig. 4.1C, asterisk) from the tumor itself (Fig. 4.1D). The dura adjacent to a meningioma often enhances as well (Fig. 4.1D