Fig. 10.1 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.

Fig. 10.2 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.

Fig. 10.3 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.

Fig. 10.4 Once the sac has been exposed, several options are available. In the simplest, the sac can be left alone in its “decompressed” state. Some surgeons inject a long-acting corticosteroid into the sac wall and between the leaves of the surrounding dura. Others open the lumen of the sac and create a shunt into either the mastoid or subarachnoid space, the latter being seldom practiced. Placement of a tube through the back wall of the sac into cerebrospinal fluid has been largely abandoned in recent years. In mastoid shunting, the lateral wall of the sac is opened with a sharp knife. While many surgeons use a Beaver blade for this maneuver, a disposable myringotomy knife or even a fine hook works well and is more economical. The endolymphatic sac does not possess a single large lumen, but is rather a network of channels partitioned by a fine reticular meshwork. These can be broken up by sweeping the lumen with a 3-mm blunt hook. A mastoid shunt can be created by inserting a thin (0.05-mm) sheet of silicon rubber as depicted in the illustration. Some surgeons advocate that the Silastic sheeting be rolled into a tube to help separate the leaves of the sac, although this can be somewhat tricky to insert. A few surgeons even insert a modified glaucoma valve, although there is little to commend about this strategy. It should be pointed out that there is much controversy concerning the efficacy of endolymphatic sac surgery, with many otologic surgeons turning away from it in recent years. While its role in the management of Meniere’s disease remains the subject of much debate, it is quite clear that results do not depend on how the sac is handled (decompression, shunting, etc.).

Fig. 10.5 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.

Fig. 10.6 Labyrinthectomy may be effective in alleviating medically refractory vestibular symptoms in an ear with no useful hearing. The goal is not to merely open the labyrinth, but to remove all five inner ear neuroepithelial elements (three semicircular canal ampullae and two otolithic organs: utricle and saccule). The procedure commences with drilling troughs parallel to the middle and posterior fossa dural plates with a cutting burr. This enables drilling toward the facial nerve with greater stability by using the side of the burr to cut through the hard otic capsule bone rather than the tip which is less controllable.