Treatment of vertigo using laser labyrinthectomy

Occlusion of the semicircular canal using argon laser

The effects of argon laser on the bony semicircular canals were studied in the guinea pig. After intraperitoneal administration of Nembutal, the bulla was opened in order to approach the lateral and posterior canals. The anterior canal was approached through the posterior fossa. The argon laser was applied through a probe which was connected to a device from HGM Medical Laser Systems. One of the three semicircular canals was irradiated one to several times by argon laser (1.0-1.5 W x 0.5 sec). Histopathologic examination of the temporal bones revealed that the semicircular duct shrank immediately after irradiation. The laser produced a charred area in the bony canal wall. The semicircular canals gradually became fibrotic and ossified and completely occluded within several weeks. Heat produced in the bony canal may be responsible for the morphologic changes. On delayed observation, the cochlea of the canal-irradiated animals showed no morphologic changes. Auditory brain stem responses were normal. Caloric stimulation using 5 ml/5 sec of ice water revealed no response in the lateral canal-irradiated animals.

Surgical anatomy of the singular nerve

Rare cases of chronic persistent positional vertigo do not respond to physiotherapy. For the treatment of these cases Gacek suggested singular nerve neurectomy as a new surgical procedure. The aim of the present study was to investigate the surgical anatomy of the singular nerve in order to evaluate the exact topography. In 25 cadaver temporal bones the posterior ampullary ("singular") nerve was prepared. The topographical correlation between singular nerve, posterior semicircular canal, and the round window membrane was evaluated. The average length of the nerve was 4.2 mm, its diameter 0.6 mm. The shortest distance between singular nerve and round window membrane was 0.7 mm in average, the nerve could be detected at a depth of 1.3 mm. The transtympanal access was impossible in 7 of 25 cases either because of its close relation to the round window or its direct course towards the ampulla. In only 5 of 25 cases was the nerve located sufficiently inferior in the round window niche for neurectomy. Thus, transtympanal singular nerve neurectomy can be performed only in selected cases. The presented data are helpful for preoperative and intraoperative decisions.

Laser labyrinthectomy

Concepts and methods of laser labyrinthectomy have been proposed based on experimental studies in which the macula utriculi was irradiated with an argon laser beam through the oval window. In our previous reports, a single application of the beam (1.5 W, 0.5 s) eradicated the guinea pig macula within 5 weeks. The contour of the membranous labyrinth was normal and intact. The human macula utriculi was approached after stapedectomy and irradiated with an argon laser in a patient who developed persistent positional vertigo after closure of a perilymph fistula. Laser singular neurectomy was also done. Hearing remained unchanged, and the patient's vertigo disappeared. The human macula sacculi, however, cannot be irradiated, because of the presence of pigment in the saccular wall. In guinea pigs, the semicircular canals were irradiated from the outside. The lateral and posterior canals were approached through the middle ear, whereas the anterior canal was approached through the posterior fossa. Argon laser irradiation (1-1.5 W, 0.5 s) to the bony canal produced a charred area with or without perforation. The semicircular duct showed shrinkage and tearing of the trabecular meshwork immediately after irradiation. Several weeks later, the canal had been obliterated by ossification. Although laser labyrinthectomy can destroy the function of individual otolithic organs and eliminate dynamic impulses of the semicircular canals, hearing can be preserved.

Perilymph fistula: concept, diagnosis and management

Perilymph fistula is caused by changes of cerebrospinal fluid pressure and/or middle ear pressure. For diagnosis, history taking is extremely important in regard to whether the occurrence of symptoms is related to physical exertion, such as straining, nose blowing, sneezing etc. A variety of symptoms are due to pathologic changes of the membranous labyrinth. Exploratory tympanotomy is needed to verify the occurrence of leakage. However, perilymph fistula cannot be excluded, even if leakage is not observed. Management consists of absolute rest and closure of the fistula. If dizziness or vertigo is intractable and long-lasting, destruction of vestibular function should be considered.