The Effect of Trauma in Causing Cochlear Losses After Stapedectomy

The Effect of CO(2) and KTP laser on the cat saccule and utricle

OBJECTIVES/HYPOTHESIS

To assess the potential carbon dioxide (CO(2)) and potassium-titanyl-phosphate (KTP) laser-related trauma to the saccule and utricle in a cat model.

STUDY DESIGN

Basic science experiment utilizing cat model.

METHODS

Twelve adult male cats were divided into two groups-CO(2) and KTP-to assess the potential saccule and/or utricle trauma with direct discharge of laser energy into the vestibule after the stapes was removed. Both groups were subdivided to assess the effects with acute sacrifice and three-month survival. Bone conduction auditory brain-stem response thresholds were used to monitor auditory function. Clinical observation was used to monitor vestibular function. The temporal bones were harvested, processed, and stained with hematoxylin and eosin (H&E) in all animals with the uninvolved side serving as the control.

RESULTS

None of the animals demonstrated changes in bone conduction auditory brain-stem responses. None of the animals in the survival group demonstrated clinical vestibular dysfunction. Saccular and utricular wall rupture was observed in all animals sacrificed acutely. None of the saccular and utricular wall ruptures were of a size and location that could be attributed to laser trauma, and none of the saccular and utricular wall ruptures were associated with neuroepithelial trauma.

CONCLUSIONS

There is no evidence of a difference between the CO(2) and KTP laser in potential laser-related trauma. Using bone-conducting auditory brain-stem response threshold and clinical monitoring of vestibular function, there was no evidence of clinical auditory or vestibular dysfunction. The histologic evidence of saccular and utricular wall rupture is more consistent with stapes extraction trauma than laser-related trauma.

Laser-assisted endoscopic stapedectomy: a prospective study

OBJECTIVE

To improve the techniques required to perform a stapedotomy without prosthesis (stapedioplasty).

STUDY DESIGN

New infrared lasers were evaluated for potential use in otological surgery in guinea pigs. A prospective human trial of 34 primary stapes operations using the Argon ion laser was performed, with 11 stapedioplasties and 23 conventional stapedotomies as controls.

METHODS

Laser-tissue interactions were evaluated for temporal bone and live guinea pig tissues, measuring crater histology and labyrinthine temperature elevations. Patients undergoing stapedioplasty had Argon ion laser cuts with endoscopic assistance made in the anterior crus and footplate to mobilize the posterior segment of the stapes while the anterior portion remained fixed.

RESULTS

Diode laser (808-nm) vaporization craters and temperature elevations in the vestibule were suitable for clinical use. Overall, stapedioplasty patients' hearing was improved with air-bone gap closure to a mean of 8.3 dB (SD +/- 9.8 dB).

CONCLUSIONS

Patients with anterior footplate otosclerosis are candidates for stapedioplasty preserving the annular ring and stapes tendon and eliminating prosthesis complications. High-resolution small endoscopes, coupled with Argon ion or diode lasers promise to improve stapes visualization, enhancing the ability to perform minimally invasive surgery on the stapes footplate.

Interactive inner-ear/middle-ear disease, including perilymphatic fistula

Pathologic interactions between the middle ear and inner ear occur with 1) congenital anomalies, 2) trauma, 3) infection/inflammation, 4) tumors, 5) granulomas, 6) ototoxic eardrops, 7) cochlear implants, 8) otosclerosis, 9) Meniere's disease (decompensated) and Meniere's disease (with perilymphatic fistula), and 10) perilymphatic hypertension. Clinical and pathological characteristics are briefly categorized in this survey. Comments are made concerning the clinical utility of exploratory tympanotomy in diagnosis and treatment of pathologic conditions in the middle ear and pathologic conditions that are interactive between middle ear and inner ear.

Survey of interactions between middle ear and inner ear

Diseases with interaction between the middle ear and inner ear include 1) congenital anomalies, 2) trauma, 3) infection/inflammation, 4) tumors, 5) granulomas, 6) ototoxic eardrops, 7) cochlear implants, 8) otosclerosis, 9) Meniere's disease-decompensated, and Meniere's disease with perilymphatic fistula, and 10) perilymphatic hypertension. Clinical and pathological characteristics are briefly categorized in this survey. The clinical utility of exploratory tympanotomy in diagnosis and treatment of middle ear pathology and middle ear/inner ear interactions is commented upon.

Influence of argon laser stapedotomy on cochlear potentials. III. Extracochlear recorded DC potential

During laser stapedotomy there is an extracochlear recordable DC deflection, which may hamper the recording of the Cochlear Microphonics (CM), or the Compound Action Potential (CAP). The investigation of the nature of this DC potential, its distribution as well as its recovery is the subject of the present paper. In contrast to the laser induced temperature alteration, this DC deflection spreads across the surface of the cochlea. Since the DC deflection only occurs during laser impact and not when perforating the cochlea with steel instruments, the most probable explanation is a heat destruction of the molecular structure of the bone.

Effect of argon laser stapedotomy on cochlear potentials. II. Alteration of the compound action potential (CAP)

The influence of the argon laser on inner-ear function during and after laser stapedotomy was investigated in guinea pigs, using the compound action potential (CAP) as parameter. With the onset of the argon laser impact, the CAP is depressed or even extinguished up to 10 s. The temporal course of subsequent CAP recovery is similar to that of endocochlear temperature recovery after laser stapedotomy, so that a direct influence of temperature increase and CAP decrease is probable. No permanent attenuation of CAP amplitude was found after a single laser perforation of the stapes footplate.

Influence of argon laser stapedotomy on cochlear potentials. I: Alteration of cochlear microphonics (CM)

In guinea pigs the cochlea microphonics (CM) were recorded during and after argon laser stapedotomy. Short termed drastic depression of CM was observed. This effect involved the entire frequency range of the cochlea. The recovery was mostly complete and often started already during laser irradiation or at the end of the laser exposure. A marked sensitivity loss of the cochlea only occurred with large stapedotomy holes followed by massive perilymph leakage. A momentary heat related instability of the entire stapes is suggested to cause the CM depression. In addition we observed a thermoacoustic effect on the CM. This laser evoked response seems to cause no harm to the cochlea.

Cochlear and vestibular lesions in capsular otosclerosis as seen in microdissection

In 24 temporal bones from patients with otosclerosis prepared by the method of microdissection and surface preparations, otosclerotic foci could be clearly seen during removal of the otic capsule. The state of activity of each focus was estimated on the basis of its consistency and vascularity. Small anterior foci constituted the most common form of involvement of the otic capsule. All were judged to be inactive, and none of them appeared to have caused obvious sensorineural degeneration. No cases of "pure cochlear otosclerosis" were seen. Sensorineural degeneration was associated with large anterior foci which reached the upper basal turn. One specimen displayed a circumscribed sensorineural degeneration in the upper basal turn, with an almost exact correspondence between the location and extent of the cochlear lesion and the site of invasion by the otosclerotic process in the bone and endosteum bordering on scala media and scala tympani. It is postulated that a toxic factor had diffused from the focus and acted directly on the organ of Corti. When multiple foci were present they were usually poorly defined. The otosclerotic process involved the round window, with new lamellar bone formation in the scala tympant of the lower half of the basal turn. The most extensive sensorineural degeneration in the entire material was seen in this group. One specimen also had severe cochlear hydrops. In three specimens large shunts were observed to connect the otosclerotic foci with the cochlear vasculature, which was severely dilated. Where otosclerosis involved the endosteum of the scala tympani, loss of vessels was observed. One specimum with extensive active capsular otosclerosis had severe sensorineural degeneration of the vestibular system. Vestibular pathology in fenestrated ears is also described. In a specimen from a patient with no caloric reaction, numerous hair cells were present in the macular organs.