Sigmoid sinus affecting retrolabyrinthine approach petroclival surgery aided by endoscopy

Objective: To study how the anatomy variation of sigmoid sinus affect the petroclival surgery aided by endoscopy. Methods: Radical mastoidectomy in 20 adult cadaveric specimens(40 sides) was carried out, exposing endolymphatic sac,sigmoid sinus and common crus. The distance from sigmoid sinus to temporal bone surface, to back wall of external acoustic meatus,to endolymphatic sac,to common crus and to endolymphatic duct,and the width and height of sigmoid sinus were all measured. Results: The distance from temporal bone surface to sigmoid sinus was (5.27±1.60) mm,4 of them were more than 7 mm (10%).The width of sigmoid sinus was (11.97±2.10) mm,3 of them were more than 15 mm (7.5%).The height of sigmoid sinus was (24.78±4.21) mm.The distance between sigmoid sinus and back wall of external acoustic meatus was (13.59±3.03) mm,5 of them were less than 10 mm(12.5%). Distance between sigmoid sinus and endolymphatic sac was (3.73±1.66) mm,from sigmoid sinus to common crus was (13.89±2.34) mm,to endolymphatic duct was (10.62± 2.09) mm. Conclusion:It is very difficult to carry the operation when there is an anterior sigmoid sinus, or inner sigmoid sinus or wider sigmoid sinus,in this case endoscopic surgery by retrolabyrinthine approach is not recommended.