Pathology as it relates to ear surgery. IV. Surgery of Menière's disease.

Conservative shunting procedures, i.e. ESS, ultrasonic irradiation and cryosurgery, are based on the assumption that there is increased volume and/or pressure of endolymph in Menière's disease. Since there is no reliable clinical test to detect endolymphatic hydrops, shunting procedures on cases without hydrops are doomed to failure. Surgery on the endolymphatic sac was not associated with fibrosis or obliteration of its lumen. Silastic shunt tubes were well tolerated by the body, and the shunt between the sac and the subarachnoid space seemed to remain open. The results of experimental surgery on the endolymphatic sac and its applicability to humans should be revised. Temporary improvement of Menière's symptom-complex may be expected from any surgical procedure on the membranous labyrinth, even in cases without endolymphatic hydrops. Post-operative serous labyrinthitis with associated biochemical changes is the cause of this improvement. The success of shunting procedures cannot be judged histologically by the position of Reissner's membrane. This membrane acts like varicose veins: once dilated, always dilated. Ultrasonic irradiation and cryosurgery of the labyrinth result in limited degenerative changes close to the site of probe application. Degenerated intact membranous walls may act as an internal otic-perotic shunt and may result in symptomatic improvement in Menière's disease. The idea of selective vestibular neurectomy and internal shunting procedures, i.e. without drainage of endolymph to the outside (mastoid) or to the inside (CSF), should be developed further. Recurrence of symptoms following shunting procedures may be due to failure of the shunt, or to the presence of endolymphatic hydrops in the non-operated ear. MF vestibular neurectomy results in complete denervation of the vestibular end-organs, without effect on the cochlea or facial nerve. Excision of Scarpa's ganglion causes retrograde degeneration in the proximal stump of the vestibular nerve, most probably to the level of the brain-stem. Recurrence of dizziness following TC labyrinthectomy is most commonly due to inadequate removal of the vestibular end-organs. The high regenerative capacity of the vestibular nerve is evidenced by the formation of traumatic neuromas in the vestibule following TC labyrinthectomy. Whether these neuromas produce symptoms is unknown. Persistent cochlear hydrops occurs following TC labyrinthectomy and TL vestibular neurectomy owing to obstruction in the hook region of the cochlea and in the ductus reuniens. This may result in persistent tinnitus and feeling of pressure in the ear.