Normal Meningeal Enhancement

Enhancement of the normal meninges on T1-weighted spin-echo magnetic resonance images (MRIs) is generally in short segments or less than 50% of the total meningeal area. Patterns of meningeal enhancement that may represent an abnormality include increased length and percentage of meningeal enhancement and nodularity. However, on post-contrast spoiled three-dimensional (3D) gradient echo (GRE) T1-weighted MRIs, a much larger percentage of the meningeal area can enhance and there can also be longer segments of enhancement and larger continuous areas of enhancement. This is thought to be due to the greater spatial resolution of the 3D GRE sequences as well as decreased signal in the calvarial diploic space on these sequences.

Abnormal Meningeal Enhancement

Postcraniotomy patients can have meningeal enhancement, presumably related to postoperative inflammation, and this can be localized to the area of the craniotomy or be generalized. Meningeal enhancement involving the dura-arachnoid and the pia can occur in pathologic conditions such as neoplasm, including lymphomatous and metastatic involvement, as well as in inflammatory or infectious processes such as bacterial or viral meningitis, sarcoidosis, chemical meningitis, subarachnoid or subdural hemorrhage, or idiopathic inflammation. In neoplastic involvement, there may be primary dural disease that seeds the subdural space, spreading to the arachnoid or the spread may be in the opposite direction. Alternatively, the neoplasm may involve the subarachnoid space hematogenously or from spread along nerves. MRI is more sensitive than computed tomography (CT) because beam hardening limits the detection of dural enhancement, particularly near the calvarium (although CT sensitivity is improved for nodular enhancement and enhancement in spaces not adjacent to the calvarium), but MRI is no more specific, and coronal or axial images are better than sagittal images.