Brain herniations into the dural venous sinuses or calvarium: MRI of a recently recognized entity.

Brain herniations into dural venous sinuses (DVS) are rare findings recently described and their etiology and clinical significance are controversial. We describe five patients with brain herniations into the DVS or calvarium identified on MRI, and discuss their imaging findings, possible causes, and relationship to the patient's symptoms. All patients were examined with MRI including high resolution pre- and post-contrast T1- and T2-weighted sequences. With respect to brain herniations we documented their locations, signal intensities in different sequences, and size. We then reviewed clinical records in an attempt to establish if any symptoms were related to the presence of these herniations. Three males and two females were examined (age range, 11-68 years). Three patients had unilateral temporal lobe herniations into transverse sinuses, one had a cerebellar herniation into the skull, and one had bilateral temporal lobe herniations into the transverse sinuses as well as a cerebellar herniation into the sigmoid sinus. In all, the herniated brain and surrounding cerebrospinal fluid (CSF) had normal signal intensity on all MRI sequences. When correlated with clinical symptoms, brain herniations were thought to be incidental and asymptomatic in three patients and two patients had histories of headaches. Brain herniations with surrounding CSF into the DVS/skull should be considered potential sources of filling defects in the DVS. We believe that they are probably incidental findings that may be more common than previously recognized and should be not confused with the more common arachnoid granulations, clots, or tumors. Two patients had headaches, but their relation to the presence of herniated brain was uncertain.