Anatomical Correlates and Surgical Considerations for Localized Therapeutic Hypothermia Application in Cochlear Implantation Surgery

Abstract

Hypothesis:Application of localized, mild therapeutic hypothermia during cochlear implantation (CI) surgery is feasible for residual hearing preservation.Background:CI surgery often results in a loss of residual hearing. In preclinical studies, local application of controlled, mild therapeutic hypothermia has shown promising results as a hearing preservation strategy. This study investigated a suitable surgical approach to deliver local hypothermia in patients utilizing anatomical and radiologic measurements and experimental measurements from cadaveric human temporal bones.Methods:Ten human cadaveric temporal bones were scanned with micro-computed tomography and anatomical features and measurements predicting round window (RW) visibility were characterized. For each bone, the standard facial recess and myringotomy approaches for delivery of hypothermia were developed. The St. Thomas Hospital (STH) classification was used to record degree of RW visibility with and without placement of custom hypothermia probe. Therapeutic hypothermia was delivered through both approaches and temperatures recorded at the RW, RW niche, over the lateral semicircular canal and the supero-lateral mastoid edge.Results:The average facial recess area was 13.87 ± 5.52 mm2. The introduction of the cooling probe through either approach did not impede visualization of the RW or cochleostomy as determined by STH grading. The average temperatures at RW using the FR approach reduced by 4.57 ± 1.68 °C for RW, while using the myringotomy approach reduced by 4.11 ± 0.98 °C for RW.Conclusion:Local application of therapeutic hypothermia is clinically feasible both through the facial recess and myringotomy approaches without limiting optimal surgical visualization.

Measurement of the Intracochlear Hypothermia Distribution Utilizing Tympanic Cavity Hypothermic Rinsing Technique in a Cochlea Hypothermia Model

“…This cooling approach was further evaluated in human temporal bones ( 10 ). A cooling effect of 4.5°C was recorded at the round window with different surgical approaches.…”

“…The otoprotective effect of localized therapeutic hypothermia on the cochlea is related to hair cell protection and nerve cell preservation as shown by histological findings ( 4 , 5 ). The usability of the custom-made device used in the murine experiments has been tested on human temporal bones achieving hypothermia at the round window and cochlear apex ( 10 , 11 ). Additionally, a finite element model based on real-time measurements in human temporal bones was calculated ( 11 ).…”

“…In ten temporal bone specimens, the custom-made cooling device was tested comparing myringotomy vs. a mastoidectomy approach ( 10 ). The cooling effect was documented with four microthermistors at round window, apex, lateral semicircular canals, as well as the mastoid bone.…”

“…The cooling effect was documented with four microthermistors at round window, apex, lateral semicircular canals, as well as the mastoid bone. This experimental setup documented temperature distribution on two probes throughout the cochleae ( 10 ).…”

“…In the current study, 12 temperature probes were positioned in the human temporal bone allowing a more detailed documentation of temperature changes. Furthermore, the use of standard surgical irrigation fluid as cooling media in the middle ear without custom-made device ( 4 , 10 ) is explored.…”