The diagnostic procedure of choice for meningioma is a gadolinium-enhanced MRI. On T1-weighted images prior to gadolinium, 65% of tumors were isointense, and 35% hypointense when compared to gray matter of the brain (Elster et al 1989). On T2-weighted images, 47% were isointense with gray matter, 35% hyperintense, and 18% hypointense. In 1 series, fibroblastic and transitional meningiomas were found more often to be hypointense, whereas meningothelial and angioblastic meningiomas were hyperintense relative to brain gray matter (Elster et al 1989). On T1-weighted images with gadolinium, these tumors typically enhance diffusely and homogeneously. The dural tail of a meningioma can be visualized to guide the surgeon in extent of resection. MRI can image vascular and neural distortion and invasion of blood vessels, particularly in the optic nerve, tuberculum sellae, and medial sphenoid ridge, and guide the neurosurgeon. Postoperatively, MRI is useful in looking for residual tumor, as such a finding would require either further monitoring or additional treatment (Newman 1994). Preliminary reports of diffusion imaging found atypical and malignant meningiomas to have lower average diffusion coefficients and to be hyperintensive on diffusion weighted images, as compared to benign meningiomas (Filippi et al 2001). Apparent diffusion coefficients correlated with tumor cellularity and were highest in benign meningiomas (Kono et al 2001).
MR perfusion is being investigated with regards to its utility in differentiated extra-axial tumors. According to a small case series, a dural-based tumor with low perfusion should suggest an alternative diagnosis to a meningioma, such as a dural metastasis (Zimny and Sasiadek 2010). Additionally, intraventricular tumors with low perfusion parameters should also suggest against the diagnosis of meningioma.
CT detects all but the smallest meningiomas and is particularly useful to document the extent of bony involvement. The tumor is hypodense to slightly hyperdense compared to brain gray matter precontrast. Calcification is present in 29% of benign meningiomas and is rarely present in malignant meningiomas (Rohringer et al 1989). Calcification can vary from punctate areas to dense calcification of the whole tumor. Homogeneous contrast enhancement occurs in 72% of benign and 36% of malignant meningiomas. Benign and malignant meningiomas can both have peritumoral edema, but it is more common and usually greater in extent in malignant meningiomas (Rohringer et al 1989).
Magnetic resonance angiography has largely replaced arterial angiography and has the ability to detect the patency of venous sinuses. In large tumors that may be candidates for preoperative embolization, arterial angiography is necessary to delineate the tumor blood supply. Tumor embolization may reduce vascularity and operative bleeding.
MRS short echo time (1)H spectra using a 1.5 T magnet has found increased reduced glutathione content compared to normal white matter and low-grade gliomas, consistent with published histofluorescence studies of tumor biopsies (Opstad et al 2003). In atypical meningiomas evaluated with MRS, 62% had an elevated lactate peak (Buhl et al 2007).