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

Systematic review of animal models of middle ear surgery

Animal models of middle ear surgery help us to explore disease processes and intervention outcomes in a manner not possible in patients. This review begins with an overview of animal models of middle ear surgery which outlines the advantages and limitations of such models. Procedures of interest include myringoplasty/tympanoplasty, mastoidectomy, ossiculoplasty, stapedectomy, and active middle ear implants. The most important issue is how well the model reflects the human response to surgery. Primates are most similar to humans with respect to anatomy; however, such studies are uncommon now due to expense and ethical issues. Conversely, small animals are easily obtained and housed, but experimental findings may not accurately represent what happens in humans. We then present a systematic review of animal models of middle ear surgery. Particular attention is paid to any distinctive anatomical features of the middle ear, the method of accessing the middle ear and the chosen outcomes. These outcomes are classified as either physiological in live animals, (e.g., behavioural or electrophysiological responses), or anatomical in cadaveric animals, (e.g., light or electron microscopy). Evoked physiological measures are limited by the disruption of the evoking air-conducted sound across the manipulated middle ear. The eleven identified species suitable as animal models are mouse, rat, gerbil, chinchilla, guinea pig, rabbit, cat, dog, sheep, pig and primate. Advantages and disadvantages of each species as a middle ear surgical model are outlined, and a suggested framework to aid in choosing a particular model is presented.

Laser irradiation of the guinea pig basilar membrane

BACKGROUND AND OBJECTIVES

The cochlea is the part of the inner ear that transduces sound waves into neural signals. The basilar membrane, a connective tissue sheet within the cochlea, is tonotopically tuned based on the spatial variation of its mass, stiffness, and damping. These biophysical properties are mainly defined by its constituent collagen fibers. We sought to assess the effect of laser irradiation on collagen within the basilar membrane using histological analysis.

STUDY DESIGN/MATERIALS AND METHODS

Four excised guinea pig cochleae were stained with trypan blue. From these, two were irradiated with a 600 nm pulsed dye laser and two were used as controls. Collagen organization was visualized using polarization microscopy.

RESULTS

Laser irradiation reduced the birefringence within the basilar membrane as well as within other stained collagen-containing structures. Larger reductions in birefringence were measured when more laser pulses were given. The effects were similar across all turns of each cochlea.

CONCLUSIONS

Laser irradiation causes immediate alterations in collagen organization within the cochlea that can be visualized with polarization microscopy. These alterations may affect cochlear tuning. Ongoing research is aimed at analyzing the effect of laser irradiation on cochlear function. It is conceivable that this technique may have therapeutic benefits for patients with high-frequency sensorineural hearing loss.

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.