Central nervous system disorders

VII./3.3.: Magnetic resonance imaging – MR

Advantage of MRI examination is that not only morphologic information is provided but also behavioural data can be obtained: DWI and perfusion, which reflects vascularisation (it can be demonstraed by CT as well).

Extraaxial meningeoma is detectable usually as a round lesion due to its expansive growth related mass effect, because its signal intensity does not differ significantly from the cerebral parenchyma neither on T1 weighted images (meningeoma can expand into the sinus as well, affectation of dural sinus must be detected because it influences the surgical plan significantly!).

Meningeomas have a slightly increased signal intensity compared to cerebral parenchyma on T2 weighted images, it is homogeneous, thin capsule can be also present. If the signal is isointense on T2 weighted image and there is no perifocal edema, these signs indicate that the composition of meningeoma is rather fibrous, „hard” (fibroblastic meningeoma). High signal refers to increased water content, „softer” consistence (angioblastic or meningothelial meningeoma).

Following contrast agent administration: Gadolinium is enhanced well. Apparently, vessels of meningeomas – being extraaxial – have nothing to do with blood-brain barrier. Arterial blood supply is provided by the dural branches of external carotid artery. As soon as meningeomas grow, they „steal” the blood from the pial and cortical branches increasingly, which refers to an increased agressivity and a liability to recur.

Dural tail is characteristic (i.e. tapered enhancement of the dura in the environment of the tumor, which can stem from reactive vascularisation, venous drainage – along the dura, but tumor propagation can be also suspected).

In the meningeomas frequently observable calcification can be demonstrated with MR only on the gradient echo images conspicuously (well visible on unenhanced CT).

Diffusion weighted imaging (DWI) is helpful in the assessment of the anticipatory behaviour of meningeomas. If motion of water molecules is restricted inside a voxel, high signal can be detected in this area (low signal on ADC mapping). It might refer to hypercellularity, which is characteristic of more agressive, atypical and recurrent meningeomas. Accordingly, DWI is able to / correlates with the (limited) histological assessment of meningeomas.