MRI of arachnoid granulations within the dural sinuses using a FLAIR pulsesequence

The purpose of the study was to assess the signal intensities of arachnoid granulations within the dural sinuses using the FLAIR sequence for differen tiation of space-occupying lesions in and adjacent to the dural sinuses. We retrospectively reviewed MR images of the brain of 1118 consecutive subjec ts, ranging in age from 0 to 93 years (mean 57.2 years). Nodules within the dural sinuses with signal intensities similar to that of cerebrospinal flu id (CSF) on both T-1 and T-2 weighted images were defined as arachnoid gran ulations. The location, signal intensity on T-1 weighted spin echo (SE), T- 2 weighted fast SE and FLAIR images, the impression on the inner table of t he skull, and the size of the lesion were assessed. 112 subjects (10.0%), a ge range 4-89 years old (mean 58.9 years), were found to have 134 arachnoid granulations. The commonest location was the transverse sinus, with 115 gr anulations (85.8%). The prevalence of the granulations showed a peak in the sixth decade of age. All granulations were isointense relative to CSF on T -2 weighted images and almost all lesions were isointense relative to CSF o n T-1 weighted images. On FLAIR images, 90.3% of the granulations were isoi ntense relative to CSF and the other 9.7% granulations were slightly hyperi ntense compared with the CSF. 21 (15.7%) subjects showed impressions on the inner table; one case involved the outer table. In conclusion, arachnoid g ranulations were isointense or slightly hyperintense relative to CSF on FLA IR. FLAIR images are helpful in differentiating arachnoid granulations from other dural sinus lesions or skull lesions which have an intensity similar to that of CSF on T-1 weighted and T-2 weighted images.