Histopathology of spontaneous brain herniations into the middle ear.

Two patients with spontaneous brain herniation into the middle ear have been operated on with a combined otoneurological approach. In case No. 1, two 2 x 3 mm arachnoid tissue herniations were found in the tegmen antri of the left ear. Six years later, a 8 x 9 mm mass consisting of prolapsed brain was removed from the right ear. The histological examination showed normal but disorganized nervous tissue. The surface consisted of middle ear mucosa or modified glial cells. More deeply numerous well preserved neurons and synapses were observed. In case No. 2, a 2 x 1 cm herniation was found in contact with the ossicles and the bony walls of the middle ear. The herniation consisted of partly degenerated nervous tissue which could explain the episode of temporal lobe seizure the patient experienced 8 years before surgery. In the world literature during the last 40 years, 29 cases of spontaneous or idiopathic brain herniation into the middle ear and mastoid have been reported. In 10, the herniations were multiple, as in our case No. 1. Case No. 1 is interesting also because the spontaneous brain herniation was bilateral.