Endolymphatic sac surgical anatomy and transmastoid decompression of the sac for the management of Ménière's disease

BACKGROUND: Decompression of the endolymphatic sac for Ménière's disease gives unpredictable results. This may be because the sac is difficult to identify and decompress accurately without causing surgical trauma. METHODS: In order to test this idea, transmastoid decompression was simulated in 5 cadaver half heads and the anatomy of the endolymphatic sac was reviewed in a further 14 specimens. RESULTS: The endolymphatic sac was found and confirmed by histology in all five simulated decompressions. A newly described feature, a trapezoid thickening of dura, was a useful guide. The review showed that the sac was constant proximally, but variable distally. The posterior semicircular canal, posterior fossa dura and sigmoid sinus are at risk during dissection. CONCLUSION: The endolymphatic sac may be identified on inspection by an overlying patch of dura, thereby reducing exploratory dissection. It is best to decompress the sac as far proximally as possible, whilst protecting the posterior semicircular canal.