26 Endolymphatic Sac Surgery
Holger Sudhoff, Henning Hildmann
The aim of endolymphatic sac surgery is to expose and drain the endolym- phatic sac using a transmastoidal approach as a treatment for Meniere’s dis- ease. This disease is characterized by episodic vertigo attacks with nausea or vomiting, sudden or fluctuating sensorineural hearing loss of different degrees and tinnitus of varying intensity. A frequent symptom is the sensation of pressure or fullness in the affected ear. The pathophysiology is commonly explained by a distension of the membranous labyrinth by the endolymph, also called endolymphatic hydrops. Bilateral Meniere’s disease is rare, often occurring within a period of 5 – 30 years in the primarily unaffected ear. Pre- operative evaluation should include electronystagmography, or balance test (ENG), electrocochleography (ECOG), brainstem evoked response audiome- try (BERA) and magnetic resonance imaging (MRI) with gadolinium to exclude an acoustic neuroma or other brain tumours as a possible source of symptoms. In spite of today’s technical knowledge, the diagnosis of Meniere’s disease still relies mainly on the clinical symptoms: fluctuating hearing loss, tinnitus, attacks of vertigo and sense of fullness in the ear. In the beginning it is often monosymptomatic, with fullness or tinnitus in the affected ear. It may also present as a sudden hearing loss. Vertigo can present very dramatically and distressingly with insatiable emesis and may be misdiagnosed as cardiac infarction, apoplexia, intoxication or severe gastrointestinal infection. The lack of aetiological knowledge about Meniere’s disease and its difficult differ- ential diagnosis explains the whole variety of medical and surgical treatment options. Its unresponsiveness to medical treatment is the indication for sur- gery. In cases with useful hearing, saccotomy is preferred before neurectomy is considered. We perform the exposure and drainage of the endolymphatic sac using a sac sialastic stent. In theory, the endolymphatic sac operation should decompress the excessive fluid within the inner ear and improve resorption of endolymph. Vertigo subsides or disappears after surgery in about 66 %, tinni- tus in 50 %, improvement of hearing in 28 % and fullness in 80 % of Meniere’s cases within 3 years of surgery. Vertigo symptoms may reappear in some indi- viduals.
Chapter26 137
Surgical Procedure
Using a retroauricular approach the mastoid is opened and the following land- marks are identified: the bony shell of the sigmoid sinus and the middle and pos- terior cranial fossa, the lateral and the posterior semicircular canals and the short process of the incus (Fig. 26.1). More experienced surgeons may use a less extended exposure. In any case, the sinus, the posterior fossa below the sinus and the lateral and posterior semicircular canals need to be clearly seen. The antrum is blocked after its exposure with Curaspon pieces to prevent bone dust entering the epitympanic and middle ear spaces. Bone dust may lead to a bony closure of the eustachian tube or the windows or to a fixation of the ossicular chain.
Anatomical Position of the Endolymphatic Sac
The dashed lines illustrate the direction of the lateral and the posterior semi- circular canals. The arch of the lateral canal is about 3 mm more lateral than that of the posterior canal. The blue line of the posterior canal should be seen.
The bone posterior to the posterior semicircular canal overlying the posterior fossa dura is removed. The distance between the posterior semicircular canal and the posterior fossa is very variable. In a well-pneumatized mastoid the endolymphatic duct leading from the sac to the vestibule can be identified. The endolymphatic sac is found below the line drawn from the lateral semicircular canal crossing the posterior canal. Avoid damage to the dura. The endolym- phatic sac is situated in a shallow groove of the posterior aspect of the tempo- ral bone as marked by the yellow lines (Fig. 26.2). It can often be identified by its change of structure of the dura of the posterior fossa. The endolymphatic duct, which is occasionally visible, has to remain intact (Fig. 26.3). The egg- shell-thin bone over the posterior fossa dura is removed with a curette. It is important to note that its superior portion of the posterior semicircular canal is closer to the posterior fossa dura than its inferior portion. The endolym- phatic sac is incised with a sickle knife and is identified after the detection of a lumen. Sometimes even experienced surgeons incise the dura accidentally, mistaking it for the clearance of the endolymphatic sac (Fig. 26.4). The position of the endolymphatic sac is often assumed as being too far superiorly. In cases of Meniere’s disease it is frequently small due to fibrosis. After identifying and opening the sac, possibly also identifying the entrance to the duct, a small tri- angular silicone sheath is inserted into the incision. The exposed area can be covered with soft tissue. Poor pneumatization and a prominent sigmoid sinus may complicate the procedure. If the sinus is very prominent, the covering bone may be thinned and fractured.
The posterior semicircular canal may be hard to find in a sclerotic mastoid.
The lateral canal can always be identified. It can be helpful to identify the blue line of the lateral canal before identifying the blue line of the posterior. The sinus can be protruding. Space can be gained by thinning the bone over the sinus and fracturing (eggshell) the bone and pushing it towards the vessel.
138 26 Endolymphatic Sac Surgery
Fig. 26.1
Fig. 26.3
Fig. 26.2
Fig. 26.4
26 Endolymphatic Sac Surgery 139
