Anatomic Study of Endolymphatic Sac On Posterior Fossa dura for Meniere’s disease and for transpetrosal skull base approach

Purpose: Compromising the endolymphatic sac in the skull base approaches impose a high risk of progressive hearing loss. The authors topographically measured the relationship between endolymphatic sac (ES) and the surrounding anatomic structures in an effort finding the safety distance while incising the presigmoidal dura. Material and methods: Three imported formalin-fixed latex-injected cadaveric heads were exercised and four mastoidectomies were performed prior to the posterior retrolabyrinthine presigmoid transpetrosal approach. The endolymphatic sac was identified as a dura-splitted pouch medical to the posterior semicircular canal (PSC). The distance between the ES and jugular bulb, anterior margin of sigmoid sinus, and superior petrosal sinus (SPS) were measured. Results: The distance between the ES and jugular bulb was expressed as ES-JB, in this study, 9.59 ± 2.70 mm (Mean ± SD); ES-SPS, 9.00 ± 1.34 mm; and ESSig, 6.61 ± 1.25 mm. The minimum of ES-Sig. is 5.08 mm. All the upper margins of ES, in this study, are below the imaginary line of horizontal semicircular canal by 3.67-5.02 mm. Conclusion: The exposure of PSC facilitates the visualization the contour of ES. In order not to injure the ES, the authors advise that the planning of incising the *Corresponding author: Cheng-Mao Cheng, M.D. Department of Neurological Surgery, Tri-Service General Hospital, National Defense Medical Center. Address: No. 325, Sec. 2, Cheng-Kung Rd., Taipei 114, Taiwan, Republic of China. Tel: +886-2-87927177; Fax: +886-2-87927178; Email: [email protected] 中西結合神經醫學雜誌 THE JOURNAL OF CHINESE-WESTERN NEUROLOGY MEDICINE 136 presigmoid dura be kept in the safety zone of 5 mm anterior to the sigmoid sinus. Keyword: Meniere’s disease, Skull base surgery