Radiologic and histologic features of the T2 hyperintensity rim of meningiomas on magnetic resonance images

A hyperintensity rim is often seen at the brain–tumor interface of meningiomas upon T2-weighted (T2WI) magnetic resonance imaging (MRI), and it is referred to as the cerebrospinal fluid (CSF) space; however, the true nature of the rim remains unclear. We surveyed the MRI findings and the histopathologic characteristics of such rims. Our study population consisted of 53 consecutive patients who underwent meningioma removal at our hospital. The intensity of the rim on MRI scans obtained with different imaging sequences was assessed in all patients. We used 22 tumors for histopathologic investigation: tissue samples were acquired from both the tumor surface and from a deep intratumoral site. Of the 53 meningiomas, 37 (69.8%) manifested a hyperintensity rim on T2WI (T2-rim). The other 16 showed neither a hyperintense nor a hypointense rim on their T2WI. An enhancement effect corresponding to the rim was observed in 28 of the 37 (75.7%) T2-rim positive tumors. While 9 among the 37 tumors with a T2-rim (24.3%) did not show rim enhancement, they showed low intensity on fluid-attenuated inversion recovery (FLAIR) images. The microvascular density in the tumor capsule was significantly greater in the 12 T2-rim and rim enhancement positive tumors than in 10 tumors that were T2-rim negative or T2-rim positive, but rim enhancement-negative (p < 0.001, Mann–Whitney U test). We found that 75.7% of T2 hyperintense rims that were detected at the brain–meningioma interface reflected a microvascular-rich capsule layer, rather than the CSF space.