The Microsurgical Anatomy Of The Infralabyrinthine Area In Lateral Skull Base Surgery

Objective : To study the configuration of the infralabyrinthine area in lateral skull base surgery. Expose the internal auditory canal via infralabyrinthine approach, and expose jugular foramen area via type A infratemporal fossa approach. To provide the anatomic information to the infralabyrinthine area for lateral skull base surgery and evidence for infralabyrinthine approach and type A infratemporal fossa approach.Methods: 20 adult cadaveric heads (40 sides) fixed with 10% formaldehyde were used in the study. Microsurgical anatomy and measurement were performed under the microscope by the mimicking infralabyrinthine approach and type A infratemporal fossa approach.Measure the important parameters of the infralabyrinthine area. Measurements were repeated three times and averaged. Acquired data were analysesed by SPSS11.0 software.Results :①The configuration of the infralabyrinthine area was variable. 26 sides were almost like a rectangle, The area was 29.98 mm~2±3.07mm~2, 11 sides were almost like a triangle due to the high jugular bulb or an anterior sigmoid sinus. The area was 18.25 mm~2±2.13mm~2.There were 3 sides which the jugular bulb just cling to the posterior semicircular canal,in these 3 cases, the infralabyrinthine area were almost disappear.②The internal auditory canal was exposed successfully in 34/40 sides of specimens via the infralabyrinthine approach. the high jugular bulb or an anterior sigmoid sinus were the primary reasons. The shortest distance from the top of jugular bulb to the posterior semicircular canal was 4.61 mm±2.56mm.③The important configuration of the infralabyrinthine area was exposed successfully in all of specimens via the type A infratemporal fossa approach.But the exposion of the posterior compartment and the posterior edge of the jugular foramen was not satisfying .It is very difficult to carry the operation when there is an anterior sigmoid sinus or high jugular bulb, in this case, surgery by type A infratemporal fossa approach is not recommended.Conclusion: Knowing the configuration of the infralabyrinthine area is favorablein lateral skull base operation and correct diagnosis.