Abstract:

Objectives　To reveal the occurrence rate of extrusion abnormality at pyramid segment of facial nerve by observation on vivisection and high-resolution CT scanning of temporal bone, and provide anatomic data for safer development of otologic surgery.　Methods　Extrusion abnormality at pyramid segment of facial nerve among 302 adult Han cases with peripheral facial palsy, who received unilateral facial nerve decompression surgery in our department from April, 2005 to April, 2011, was observed and analyzed under operating microscope. The value of CT in the discovery of the abnormality was evaluated by the comparison of preoperative high-resolution CT data.　Results　Extrusion abnormality at pyramid segment of facial nerve was found to be presented among 14 cases during the surgery, accounting for 4.6% among all cases. Only one case with such abnormality was discovered by preoperative axial CT scanning of temporal bone, while 100% of the abnormality could be found by coronal reconstruction preoperatively.　Conclusions　Extrusion abnormality at pyramid segment of facial nerve is available among 4.6% Han adults. High-resolution CT scanning of temporal bone should be performed routinely prior to mastoid surgeries, and it's necessary to perform coronal reconstruction to find such abnormality. During mastoidectomy, the traditional skill with horizontal semicircular canal plane as the deep plane for safe dissection is not reliable for Han population, with the risk of iatrogenic facial nerve injury. 

Key words: Facial canal, Pyramid segment, Decompression surgery, Anatomic variation