Selective vestibular ablation in monkeys by laser irradiation

Abstract

Following bilateral simple mastoidectomy, eight adult squirrel monkeys were subjected to argon laser irradiation (output wavelength of 488 nanometers) of the horizontal or posterior semicircular canals. Penetration of the bony canal wall and damage to the membranous labyrinth was achieved if multiple or superimposed burns were made (one watt bursts with durations from 0.2 to 1 second). The major morphologic effect of the penetrating lesions was a mild to prolific growth of fibrous tissue restricted to the immediate site of irradiation. Endolymphatic ducts were blocked by collapse of one membranous wall against the other, by filling in of the lumen with fibrous growth of the duct walls or by constriction caused by overgrowth of surrounding fibrous tissue filling the perilymphatic space. Blocking of the duct, however, can not account fully for functional vestibular changes following irradiation, because some dysfunction occurred in the absence of any discernible structural abnormality. On the other hand, some function remained when ducts were completely occluded. Except for the control ear animal, all others exhibited slight to moderate ataxia and loss of acrobatic ability for several days after irradiation. No spontaneous nystagmus was detected in any monkey. All animals of our series, even those with no apparent morphological changes, were characterized by at least temporary reduction of caloric‐induced nystagmus, but only two showed complete absence of responses. All monkeys showed a change in the direction of caloric responses from horizontal to rotary or mixed, and vigor of the responses lessened considerably. Monkeys having penetrating lesions of the posterior canal exhibited subnormal postrotatory nystagmus when rotated in a forward direction with vertical canalsplaced in the horizontal plane. Two of the monkeys were trained to track their pure tone detection thresholds by means of an automated, single‐lever conditioned‐avoidance procedure. Bone conduction hearing was normal after irradiation except for a 16 db threshold shift at 2,000 Hz in one animal. On the basis of our experience with squirrel monkeys, there would appear to be no hazardous or life‐threatening side effects of laser surgery of otic structures when done in this manner. Serious consideration should be given by otologists to the experimental application of lasers for human microsurgical purposes.

Selective Vestibular Ablation by KTP Laser in Endolymphatic Hydrops

“…The goal of this study was to examine the feasibility of preserving hearing in hydropic ears with TSCA using the KTP laser. Similar to previous observations of nonhydropic ears, 22,23 we found that the KTP laser effectively occluded the treated semicircular canal. In contrast to the observations from conventional or CO 2 laser‐mediated selective ablation in hydropic ears, KTP‐TSCA was not complicated by any significant, lasting HL.…”

Laser‐Assisted Endoscopic Stapedectomy: A Prospective Study

“…The argon ion laser was studied for potential intralabyrinthine injury by Stahle et al, 72 who performed guinea pig studies with the argon laser and found it was possible to destroy the intralabyrinthine neuroepithelium without damage to overlying otic capsule. Wilpizeski et al 73 in 1972 fenestrated the horizontal and posterior semicircular canals in eight monkeys with the argon ion laser. There was intralabyrinthine local fibrous reaction at the irradiation site, but it was surprising that there was only a limited decrease in the animals' vestibular function and no significant reduction in hearing.…”

Hearing Preservation With Labyrinthine Ablation in Otitis Media

“…Over the past decade a great deal of work has been done on hearing preservation with selective occlusion or ablation of the semicircular canals. 1–25 Posterior semicircular canal occlusion has gained widespread popularity in the treatment of intractable benign paroxysmal vertigo because of its high rate of success and very low rate of hearing loss. 5–16,18 Selective ablation of the semicircular canals has also been used to improve access to the petrous apex and clivus tumors, also with low rates of hearing loss.…”