The endolymphatic sac (ELS) can be found in a thickened portion of the posterior fossa dura medial to the sigmoid sinus and inferior to the posterior canal. A classic landmark that consistently defines the upper boundary of the ELS is known as “Donaldson’s line”. This line is drawn through the lateral semicircular canal (SCC), which bisects the posterior SCC; the ELS is usually at and below this line.

After completing a cortical mastoidectomy with identification of the lateral SCC, the posterior SCC should be delineated by removing the surrounding perilabyrinthine air cells. The approximate location of the vertical segment of the fallopian canal can be identified by the relative anatomy of the SCCs and the posterior canal wall, which is gradually thinned out. The fallopian canal is further delineated from behind while skeletonizing the sigmoid sinus and removing the retrofacial air cells

Stay updated, free articles. Join our Telegram channel

Join