Study On The Characteristic Of Internal Auditory Canal And Its Drilling In Patients With Acoustic Neuroma

OBJECTIVE:To analyze the relationship between the changes in the internal auditory canal(IAC)caused by acoustic neuroma and preoperative clinical symptoms,and to describe a method of safe drilling of the posterior wall of the internal auditory canal(IAC),so as to expose the fundus of internal auditory canal.METHODS: 63 patients with acoustic neuroma were enrolled into This retrospective study between January 2014 and July 2018.Preoperative bone-window CT was used to classify the change in the IAC into five categories:normal,symmetrical widening,funnel-shaped widening,oval-shaped widening,extensive destruction.MRI of the 63 patients were retrospectively studied to analyze tumor characteristics(such as tumor volume,cyst formation),preoperative clinical presentation(such as Facial nerve dysfunction,Hearing loss,Disequilibrium,Tinnitus,trigeminal nerve dysfunction.).The relationships between the IAM change and these parameters were evaluated.preoperative high-resolution CT scan was used to delineate a Safe Zone for drilling the Posterior Wall of Internal Acoustic Meatus in Surgery of acoustic neuroma via the Retrosigmoid Suboccipital Approach and make the required measurements for the drilling procedure.Statistical analysis was performed using 20.0 SPSS.The data were statistically analyzed using the chi-square test for independence,Kruskal-Wallis test,Mann-Whitney U test,paired-samples T test and one-factor analysis of variance(ANOVA).Statistical significance was set at P<0.05.RESULTS: The mean grade of facial nerve function(facial nerve function was evaluated by House-Brackmenn Classification System)in preoperatve patients with extensive destruction(1.78±0.434)were higher than in patients with categories of IAC respectly,and the difference was significant(P=0.013<0.05).The incidence of the deafness in Patients with extensive destruction of is 80%,and higher than patients with other categories of IAC.The incidence of the deafness was significantly different between the five groups(P=0.012<0.05).But there was no significant difference between the change in the IAC and other clinical presentations.the distance of X was 33.59±0.85 mm,DA was 7.9±0.21 mm,DB was 8.8±0.31 mm,AB was10.2±0.186 mm,the degree of ?ABD was 51.1±1.3o,and the area of ?ABD was35.3±1.9mm2.the distance Y of affected side was3.54±0.438 mm,the distance Y of unaffected side was 5.07±0.349 mm,and the distance Y was significantly different between the affected side and unaffected side.(P=0.007<0.05)CONCLUSIONS: the severity of internal auditory canal destruction In patients with acoustic neuroma is correlated with the degree of preoperative facial nerve function and deafness.The more severe the damage of acoustic neuroma to the bone around the inner auditory canal,the more severe the preoperative facial paralysis and hearing loss?Preoperative high-resolution CT scan can help to delineate a Safe Zone for Drilling the Posterior Wall of Internal Acoustic canal,so as to protect Labyrinth structures and jugular bulb.And It is advise that the size of bone flap should not be too small,So that we have enough space for the operation to protect Semicircular canal and vestibular aqueduct.