Brain Herniation into Arachnoid Granulations: Clinical and Neuroimaging Features.
Brain herniation into presumed arachnoid granulations (BHAG) is an increasingly recognized entity. Though it has previously been described as isointense to brain matter on magnetic resonance imaging (MRI), we have encountered 21 cases in our clinical practice, many of which have signal abnormality in the herniated or adjacent parenchyma. We performed a systematic analysis on these cases to further understand the clinical significance.



This is a retrospective analysis of cases collected from our clinical MRI practice. Each case was evaluated for location, size, lobe of origin, associated signal abnormality, symptoms, and the presence or absence of intracranial hypertension.



Twenty-one cases of BHAG identified in 16 patients. Seven cases (7/21, 33%) demonstrated signal abnormality in the herniated or underlying parenchyma. On serial imaging, the size of herniation either fluctuated (2/10, 20%) or stayed the same (8/10, 80%). The associated signal abnormalities increased (1/5, 20%), decreased (1/5, 20%), or remained stable (3/5, 60%). Four patients (4/16, 25%) had signs/symptoms that could be associated with the BHAG. Ten patients (10/16, 63%) had either imaging findings or clinical signs that could be associated with intracranial hypertension.



In contrast to previously reported cases, our study demonstrates that BHAG can be associated with MRI signal abnormalities of the herniated and adjacent brain. Symptoms are typically absent, though may be present in a small subset of patients, regardless of the presence of signal change or encephalomalacia of the involved brain. Indirect evidence of intracranial hypertension is present in a majority of patients but completely lacking in others.
Department of Radiology, Mayo Clinic-Rochester, Rochester, MN. liebo.greta@mayo.edu.
Greta B
GB
Liebo
Department of Radiology, Mayo Clinic-Rochester, Rochester, MN.
John Jack I
JJ
Lane
Department of Neurologic Surgery and Otolaryngology, Mayo Clinic-Rochester, Rochester, MN.
Jamie J
JJ
Van Gompel
Department of Radiology, Mayo Clinic-Rochester, Rochester, MN.
Laurence J
LJ
Eckel
Department of Radiology, Mayo Clinic-Rochester, Rochester, MN.
Kara M
KM
Schwartz
Department of Radiology, Mayo Clinic-Rochester, Rochester, MN.
Vance T
VT
Lehman
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001099:Arachnoid / Q000000981:diagnostic imaging* / Q000473:pathology; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology; D001927:Brain Diseases / Q000000981:diagnostic imaging* / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006547:Hernia / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging; D012189:Retrospective Studies; D055815:Young Adult
Brain herniation; arachnoid granulation; encephalocele