Rim enhancement of meningiomas on fast FLAIR imaging.

We investigated the enhancement patterns of meningiomas on fast fluid-attenuated inversion-recovery (FLAIR) images and related them to the size and histology of the tumour and the associated oedema. We studied 30 meningiomas with T2-weighted fast spin-echo (SE) images plus T1-weighted SE images with magnetisation-transfer saturation and fast FLAIR before and after contrast enhancement at 0.5 tesla. There were 21 meningiomas (70%) which showed peripheral (rim) enhancement on fast FLAIR, while only one, which showed heavy central calcification, enhanced peripherally on the SE images. Of the meningiomas with capsular enhancement on fast FLAIR 20 (95%) were more than 2 cm in diameter. The nine 9 smaller meningiomas enhanced homogeneously. This difference was statistically significant pattern ( P<0.01). All meningiomas which had associated oedema showed the capsular pattern although their number (6; 20%) was to small to analyse statistically. Only 11 (36%) tumours were examined histologically; peripheral enhancement was observed in all types of meningioma. This pattern may help to differentiate meningiomas from other extra-axial masses.