Endolymphatic Sac Surgery

In preparation for exposure of the endolymphatic sac, an intact canal wall mastoidectomy is performed. In contrast to many drawings which appear in otologic texts, the sac does not reside on the posterior fossa dura superficially in the mastoid. Instead it is positioned rather medially and sits inferior to the labyrinth. Surgical exposure of the sac is carried out through a roughly rectangular window (dashed line) which, when pneumatized, is known as the retrofacial air cell tract. This is bounded anteriorly by the mastoid segment of the facial nerve, posteriorly by the posterior fossa dura, superiorly by the posterior semicircular canal, and inferiorly by the jugular bulb. ES, endolymphatic sac; JB, jugular bulb; PFD, posterior fossa dura; 7, facial nerve; PSCC, posterior semicircular canal; LSCC, lateral semicircular canal; SSCC, superior semicircular canal.
A patch of posterior fossa dura is bared beneath the inferior margin of the posterior semicircular canal. It is usually not necessary to skeletonize this canal in order to gain adequate exposure. When an extensive retrofacial cell tract exists, the pneumatized cells can be safely and rapidly removed en route to the sac. The lower margin of the otic capsule can usually be appreciated by its denser nature, its more yellow color, and its fine pattern of superficial blood vessels.
The goal of sac decompression is not merely to identify its edge, but rather to remove bone completely from its lateral surface along with 1 to 2 mm of surrounding dura. Care must be taken to avoid injury to the endolymphatic aqueduct where it penetrates the otic capsule superiorly. While the entire sac is accessible in the great majority of cases, in a few percent it may lie either predominantly or even completely deep to the posterior semicircular canal. A small vessel typically traverses the apex of the sac. It is often injured during bone removal and must be controlled with either bipolar cautery or an absorbable gelatin sponge pledget.
When the sigmoid sinus is anteriorly placed, it can obstruct visualization of the retrofacial cell tract (dashed lines). In extreme cases, the sinus may even contact the posterior aspect of the ear canal. To accommodate for the anatomical variation of an anteriorly placed sigmoid sinus, bone is removed from the vessel’s surface with a diamond burr and it is gently retracted. This maneuver provides ample access to the region of the endolymphatic sac.

 

Dr. Jackler and Ms. Gralapp retain copyright for all of their original illustrations which appear in this online atlas.  We encourage use of our illustrations for educational purposes, but copyright permission should be sought before publication or commercial use. To request permission for publication or commercial use please contact Christine Gralapp (eyeart@chrisgralapp.com, https://www.chrisgralapp.com).