Objective: To elucidate the role of facial recess bony plate in the thermal transmission route from external auditory canal to lateral semicircular canal during caloric stimulation test, we performed the test on patients before and after removal of the plate, i.e. posterior tympanotomy. In the present study, we adopted facial nerve decompression (FND) as posterior tympanotomy without surgery-induced inner ear damages and cochlear implantation (CI) as posterior tympanotomy with surgery-induced inner ear damages.
Methods: Between 1999 and 2003, we performed FND on 19 patients with unilateral facial nerve paresis due to Bell's palsy (n=7), Ramsay-Hunt syndrome (n=7) or facial nerve trauma (n=5) at Osaka Rosai Hospital. We also performed CI on 34 patients with bilateral deafness at Osaka University Hospital. To examine effects of FND or CI on caloric responses in vestibular periphery, caloric stimulation (30 degrees C cold water and 44 degrees C hot water) with ENG was performed twice, just before and 6 months after surgery in each subject. The caloric-induced nystagmus was recorded by using ENG under dark and open-eyes situation to calculate the maximum slow phase eye velocity.
Results: In cases of FND (n=19), there were significant decreases between pre- and post-operative 30 degrees C responses (t-test: p=0.049<0.05). There were no significant differences between pre- and post-operative 44 degrees C responses (t-test: p=0.467>0.05). In cases of CI (n=34), there were significant changes between pre and post-operative responses in both temperatures (t-test: p<0.0001 in 30 degrees C; p=0.011<0.05 in 44 degrees C).
Conclusion: The insertion of electrodes during CI did some damages to vestibular peripheral function and reduced both hot and cold caloric responses according to the results of CI. However, the procedure during posterior tympanotomy could also decrease caloric responses especially in cold stimulation according to the results of FND. Therefore, we should consider the effect of structural change in temporal bone on the thermal transmission in case of evaluation of vestibular peripheral function by using caloric stimulation test.