Triple semicircular canal occlusion in guinea pigs with endolymphatic hydrops.

HYPOTHESIS Triple semicircular canal occlusion will eliminate rotatory stimulation to the vestibular peripheral system (as it blocks endolymphatic fluid movement) and therefore release rotatory vertigo attack. This surgery is safe in ears with endolymphatic hydrops. BACKGROUND Semicircular canal occlusion has been used as an alternative treatment of intractable benign paroxysmal positional vertigo with varied success. Triple semicircular canal occlusion in animal models blocks the responses of the semicircular canals to rotation and spares cochleae and the otolithic apparatus. This result suggests that triple semicircular canal occlusion is a prospective method in vertigo management for patients with Ménière's disease. However, the effectiveness and safety of triple semicircular canal occlusion has not been fully evaluated in ears with endolymphatic hydrops. METHODS Endolymphatic hydrops was established in 20 guinea pigs by endolymphatic sac obliteration. Triple semicircular canal occlusion was performed in 12 of them 120 days after endolymphatic hydrops surgery, whereas 8 others were killed for morphologic observation to confirm endolymphatic hydrops. Auditory and vestibular functions were monitored from the time before endolymphatic hydrops until 1 month after triple semicircular canal occlusion. Endolymphatic hydrops and canal occlusion were confirmed by morphologic observation. RESULTS Successful establishment of endolymphatic hydrops was indicated by mild elevation of the auditory brainstem response threshold and tentative asymmetry in nystagmus. Endolymphatic hydrops was confirmed by cochlear morphology in all eight animals that were killed 120 days after endolymphatic hydrops surgery. After triple semicircular canal occlusion, all 12 animals showed spontaneous nystagmus with a slow component toward the side that had been operated on, head tilt, rotated walking, and tentative asymmetry in rotatory nystagmus. The static symptoms disappeared within 1 month after triple semicircular canal occlusion. Caloric nystagmus was only slightly reduced after endolymphatic hydrops as compared with the contralateral ears but could not be elicited at all after triple semicircular canal occlusion. No significant elevation in auditory brainstem response threshold was found after triple semicircular canal occlusion. The canal occlusion and endolymphatic hydrops were confirmed in all surgical ears. CONCLUSION Triple semicircular canal occlusion is effective for eliminating the response of semicircular canals to rotation and caloric stimulation and is safe in ears with endolymphatic hydrops. Also, the static compensation to the disequilibrium is quick and complete. These results suggest that triple semicircular canal occlusion should be an option for controlling rotatory vertigo in Ménière's disease.