Endolymphatic Sac Decompression

0. Introduction and Preparation

1. Anesthesia
• The surgery is performed under general anesthesia.
• The endotracheal tube should be secured to the patient’s mandible on the side opposite of the planned surgery.
• Perioperative antibiotics should be administered within one hour of the incision.
• Because facial nerve monitoring is used, the patient should not be paralyzed during the procedure.
2. Patient Positioning
• The patient will be rotated 180 degrees with the head opposite of anesthesia.
• The patient is laid supine on the operating table, and straps are placed after tucking the arms so that the table can be rotated with the patient secured. A shoulder roll is not required. The patient’s head should be rotated to the opposite side so that the mastoid is parallel to the floor.
3. Facial Nerve Monitoring
• Ground and stimulation electrodes are placed in the subcutaneous tissue overlying the sternum.
• The orbicularis oculi and the orbicularis oris muscles are monitored by placing ipsilateral electrodes into these muscles.
4. Prepping the Patient
• The patient’s skin behind the ear is cleaned with an alcohol solution after any hair overlying the postauricular area is shaved.
• Mastisol is applied in four quadrants surrounding the ear, and adhesive drapes are applied to block out the ear and mastoid.
• A cotton ball is placed in the external auditory canal, and the area is prepped with Betadine solution.
• Four sterile towels are used to block out the area, and a split drape is placed. A single Ioban drape is placed over the field.

1. Postauricular Incision

1. Local Anesthetic Injection
• A C-shaped postauricular incision should be drawn with a marking pen approximately 1 cm posterior to the sulcus. Several perpendicular lines may be drawn with the marker to help reapproximate the skin during closure.
• The skin and subcutaneous tissue should be infiltrated with local anesthetic consisting of 1% lidocaine with epinephrine in a concentration of 1:100,000.
• Approximately 5–10 minutes should pass to allow for the vasoconstrictive properties of the epinephrine to take effect.
2. Incision
• The incision should be carried through the skin and the subcutaneous tissue to a plane just superficial to the temporalis fascia. This should be performed inferiorly towards the mastoid tip and superiorly above the temporal line.
• With the muscle exposed, the subcutaneous tissue can be retracted with a self-retaining retractor.
3. Subperiosteal Flap
• The mastoid muscle-periosteal layer should then be incised in a “7-fashion” through the muscle and directly onto the bone using monopolar cauterization. Care should be taken inferiorly to palpate for the mastoid tip to ensure that the instrument is not plunged more deeply.
• An anterior based muscle-periosteal flap can then be elevated using a Lempert elevator to expose the posterior bony ear canal and the mastoid cortex.
• The linea temporalis should be exposed superiorly to help approximate the level of the tegmen mastoideum.

2. Mastoidectomy

• The sterile operating microscope should be brought into the field in order to facilitate microdissection.
• With a 5-mm cutting burr on the drill, an intact canal wall mastoidectomy should be performed down to the level of the antrum and the horizontal semicircular canal. The dissection should begin superiorly near the temporal line to help demarcate the superior limit of the dissection.
• The cortical mastoidectomy should be carried inferiorly directly behind the bony ear canal. The cortical bone is removed and widely saucerized with the deepest level of the dissection in the anterosuperior quadrant below McEwan’s triangle.
• When the antrum is reached, the cutting burr should be exchanged for a diamond burr to facilitate more cautious dissection. With this in place, the horizontal semicircular canal, sigmoid sinus, and tegmen mastoideum can be dissected.
• After thinning the posterior external auditory canal, the facial nerve can be identified just distal to the second genu as it turns into the vertical mastoid segment. A thin layer of bone should be left along the course of the facial nerve.
• The bone overlying the sigmoid sinus and posterior fossa dural plate are thinned by removing the retrofacial air cells.

3. Endolymphatic Sac: Identification & Decompression

• When looking for the endolymphatic sac (ELS), consider Donaldson’s line, an imaginary line that can be drawn along the horizontal semicircular canal that bisects the posterior semicircular canal. In the area where this line meets the sigmoid sinus, the ELS can be estimated just anterior and inferior to this junction.
• As the bone in this area is removed, note a thickened area of the posterior fossa dura that denotes the sac. When the bone is compressed, gently pressing on the sac may reveal the duct running anterolaterally as it tents the dura in the direction of the posterior canal.
• With the ELS completely exposed, the sac should be opened using a sickle knife along the posterolateral aspect.

4. Silastic Stent

1. Shaping the Stent
• A T-shaped stent is fashioned from a Silastic sheet.
2. Placement of Stent
• The upper part of the “T” is folded onto itself and placed within the sac, so that in trying to unfurl itself, it stents the lateral layer of the sac open.
• A piece of Gelfoam is placed over the surgical site.

5. Closure

• The periosteal layer is closed in interrupted fashion with a 3-0 Biosyn suture. The corner of the “7-incision” is brought together first, followed by the other areas. This does not need to be a watertight closure, but this layer should be well-approximated.
• Using the same 3-0 Biosyn suture, the subcutaneous layer is also closed. This is performed with deep interrupted suture to bury the knot, while reapproximating the skin edge.
• A thin layer of Steri-Strips should be placed along the length of the incision.
• A House-mastoid dressing should be fashioned from 4x4 gauze. This dressing is placed over the ear and mastoid being operated on, and secured around the head using two inch Kling roll gauze. Care should be taken to ensure that this dressing goes below the occiput to help prevent it from sliding off of the vertex. This dressing is left in place for 24 hours and removed at home.
• Patients are discharged on the day of surgery.
1. Postoperative Restrictions
• The patient is sent home on a week of antibiotics (Keflex). They are also given anti-nausea medication as well as pain medication (Norco).
• They are advised to perform no heavy lifting (greater than 8–10 pounds) for 2–3 weeks after surgery.
• They are seen 3 weeks after surgery to assess the wound, and an audiogram is obtained at three months to reassess hearing outcomes.