The Microsurgical Anatomy Of The Internal Auditory Canal And The Petrous Apex Area Via The Infralabyrinthine Approach

Objective:To study the configuration of the auditory canal(IAC) and the petrous apex area through the infralabyrinthine approach.To provide anatomic and imaging information for this approach.And to sutdy the superiority and safety of this approach and the modify infralabyrinthine approach.Methods:High-resolution CT scans temporal bones of 20 adult head specimens.The related data were measured.The following structures were observed:the extent and scope of gasification of mastoid,the situation of jugular bulb and sigmoid sinus.All data were retained and photographed.Expose the auditory canal,the petrous apex area and jugular foramen area.Microsurgical anatomy and measurement were performed under the microscope by the infralabyrinthine approach and the modify infralabyrinthine approach.Summarise the experiences in the course of simulated surgery.Results:1.CT scan:②the distanse from the vertical segment of facial nerve to the middle sigmoid sinus was(7.26±1.58)mm;②the distanse from the posteriors emicircular canal to the top of jugular bulb was(5.12±1.68)mm;③the distanse from the posterior semicircular canal to the inner door was(12.25±3.78 )mm;④the distanse from the inner door to the jugular foramen was(6.74±1.96 )mm;⑤the length of internal auditory canal was(10.86±1.98 ) mm;⑥the distanse from the top of jugular bulb to the jugular foramen was(6.12±2.08)mm.Anatomic measurement:the corresponding data was(6.84±2.02) mm,(4.56±2.35) mm, (13.28±2.36) mm,(5.12±1.27) mm,(9.78±1.17) mm,and(5.82±3.06) mm.The data of temporal bone structures from CT scan were highly coincident with the data from anatomic measurement. 2.①The shape and size of removed bone through the infralabyrinthine approach had larger individual variability.6 sides which the jugular bulb just cling to the posterior semicircular canal or even higher than the posterior semicircular canal should not be exposed IAC through the infralabyrinthine approach.However,found some of removed bone in some case that pressured the jugular bulb.Of course,this could only operate in the specimens②The internal auditory canal was exposed successfully in 34/40 sides of specimens via the infralabyrinthine approach,the possibility of exposing internal auditory canal was 85%.The perspective of surgical approach was 28.42°±2.64°(25.78°～31.06°).③The specimens that could be exposed the auditory canal through the infralabyrinthine approach are better gasification.④The distanse from the vertical segment of facial nerve to the middle sigmoid sinus was the horizontal diameter of removed bone through the infralabyrinthine approach,the average of the distanse was 6.84 mm;the distanse from the posteriors emicircular canal to the top of jugular bulb was the vertical diameter,the average of the distanse was 4.56mm,it was the decisive factor of this approach.⑤The possibility of exposing internal auditory canal through the modify infralabyrinthine approach becomes 90%. The area was larger than before.Conclusion:1.The data of temporal bone structures from CT scan were highly coincident with the data from anatomic measurement.Therefore,the detailed petrous bone CT scan is a reliable reference to direct the operation through the infralabyrinthine approach.2.The infralabyrinthine approach is a significant application of clinical surgery.The modify infralabyrinthine approach makes the area of removed bone larger,and the indicatio wider.3.In spite of the infralabyrinthine approach has much advantage,knowing the configuration of the temporal bone is favorable due to the complex structure of the temporal bone.