Specific Imaging Findings

Meningioma is the prototype extra-axial dural-based mass. Its extra-axial location is ascertained by a large dural base, obtuse angles at dural margins, CSF clefts, buckling of the adjacent cortex, and vessels between the tumor and brain. The mass is isodense to slightly hyperdense, with possible calcifications and hyperostotic changes of the adjacent bone on CT. The T2 signal usually ranges from slightly hypointense to mildly hyperintense, T1 signal is isointense to the cortex, with dense and homogenous contrast enhancement on both MRI and CT. Calcifications may lead to heterogeneous MRI appearance, while true cystic and necrotic changes are rare. These tumors frequently show adjacent dural thickening, the so-called “dural tail”, a nonspecific sign. Perfusion MR imaging shows high rCBV and incomplete T2* signal drop recovery to baseline, typical for non-glial neoplasms. A characteristic but not very frequent alanine peak at 1.3–1.5 ppm is found on MRS. CTV and MRV are helpful in assessing dural sinus invasion and patency. These neoplasms may also have a flat appearance along the thickened dura (“en-plaque” meningioma), or grow exclusively within the diploic space with very high CT density and low MRI signal (intra-osseous meningioma). Vasogenic edema in the adjacent compressed brain, and peritumoral collections of trapped CSF may be present. Tumors can also extend extracranially through the skull base foramina. T2 hyperintensity suggests a more rapid tumor growth.