Brain herniation into arachnoid granulations: an underrecognized posterior fossa finding.

PURPOSE: To evaluate the prevalence, imaging characteristics, and associated findings of brain herniation into arachnoid granulations (BHAG) using the 3D driven equilibrium (DRIVE) sequence on a 3T MRI system. MATERIALS AND

METHODS

This retrospective study included 695 patients who underwent temporal MRI between January and May 2024. Imaging findings were reviewed by two experienced radiologists. BHAG prevalence, locations, associated parenchymal damage (gliosis/encephalomalacia), and detectability with conventional MRI sequences were assessed. Demographic data and clinical information were also recorded.

RESULTS

BHAG was identified in 7.3% of cases (51/695) in the posterior fossa. Patients with BHAG were older than those without (p=0.003), with no gender preference (p=0.259). Cerebellar herniations were most frequent (47.1%), followed by temporal (45.1%) and occipital lobe herniations (17.6%). Parenchymal damage was observed in 25.5% of patients with BHAG. BHAG was undetectable with conventional MRI sequences in 40% of cases.

CONCLUSION

BHAG is a common incidental finding in brain MRI and presumably not associated with any symptoms. 3D-DRIVE sequence has a higher sensitivity, particularly with the high-field imaging systems, in the detection of BHAG.