Endolymphatic Shunt Placement Technique

Updated: Mar 16, 2015
  • Author: Matthew Ng, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
  • Print
Technique

Approach Considerations

Complete mastoidectomy is performed with the additional steps to skeletonize the sigmoid sinus from sinodural angle inferiorly toward the jugular bulb. The posterior fossa dura anterior to the sigmoid sinus is also skeletonized. The anterior limit of dissection is the posterior semicircular canal and mastoid segment of the facial nerve. There is no need to blue-line the posterior semicircular canal.

Right mastoid cavity landmarks. Note infralabyrint Right mastoid cavity landmarks. Note infralabyrinthine position of the endolymphatic sac. 1. Sigmoid sinus. 2. Tegmen mastoideum. 3. Endolymphatic sac

The mastoidectomy performed during endolymphatic sac surgery is usually unhindered by any chronic obstructive or inflammatory disease in the mastoid. Therefore, identification of the relevant mastoid anatomy should be straightforward.

One of the key anatomical landmarks used in endolymphatic sac surgery is Donaldson line. This is an imaginary line drawn posteriorly from the course of the horizontal semicircular canal. The line should course perpendicular to that of the posterior semicircular canal. The endolymphatic sac is located inferior to this line.

Donaldson line used to approximate location of end Donaldson line used to approximate location of endolymphatic sac.
Next:

Endolymphatic Shunt Placement

With the patient’s head turned opposite the side of the affected ear, the entire auricle and postauricular area is prepared and draped. Local anesthetic with vasoconstrictor (eg, 1% lidocaine with 1:100,000 epinephrine) is injected in the area of the planned postauricular incision. The incision is carried back behind the auriculocephalic crease the same distance as that for routine mastoidectomy for chronic ear disease, approximately 1 cm.

The plane lateral to the temporalis fascia is entered.

A periosteal T-shaped incision is created along the linea temporalis. A perpendicular incision from the linea temporalis incision is extended inferiorly toward the mastoid tip.

The musculoperiosteal flap is elevated forward until the posterior bony external auditory canal is reached. The remainder of the musculoperiosteum is elevated posteriorly and superiorly to expose the lateral mastoid cortex in preparation for mastoidectomy.

Mastoidectomy is commenced with the otologic high-speed drill using cutting burs for aggressive bone removal and using diamond burs as the approach nears critical structures. The tegmen mastoideum, sigmoid sinus, and sinodural angle are skeletonized, and the posterior bony ear canal wall is thinned. The mastoid tip air cells are opened to the level of the digastric ridge, which should approximate the level of the descending segment of the facial nerve as it courses toward the stylomastoid foramen.

Bone removal anterosuperiorly proceeds toward the mastoid antrum as Koerner septum is identified and opened. The prominence of the horizontal semicircular canal is identified. The zygomatic root toward the epitympanum (posterior epitympanotomy) is opened to identify the body and short process of the incus that will provide additional landmarks for orientation within the mastoid.

Bone removal over the sigmoid sinus can now continue inferiorly toward the jugular bulb. The mastoid segment of the facial nerve is skeletonized. This will assist in locating the retrofacial air cells and protecting the facial nerve from injury.

Using the prominence of the horizontal semicircular canal, Donaldson line is identified to approximate the position of the endolymphatic sac. The endolymphatic sac should be located inferior to this line.

The endolymphatic sac usually presents as a dural duplication or dural thickening during exposure of the posterior fossa dural plate between the sigmoid sinus posteriorly and the posterior semicircular canal anteriorly. Removal of the retrofacial air cells, when present, will help gain more exposure to locate the endolymphatic sac. The endolymphatic sac is typically located deep and inferior to the posterior semicircular canal (infralabyrinthine). When the endolymphatic sac is located, it can be followed forward toward the endolymphatic duct that courses just medial of the posterior semicircular canal.

Once the endolymphatic sac is identified, the sac may be incised with a sharp sickle knife, and the lumen, characterized by its glistening and shiny appearance, is entered with an annulus elevator or blunt probe.

The right endolymphatic sac is opened. Shunt may b The right endolymphatic sac is opened. Shunt may be placed inside the lumen of the sac.

A silicon sheet (thickness 0.010 in or 0.05 mm) is cut and positioned inside the lumen. A commercially available shunt may also be used . There is usually no need to secure this silicone fashioned shunt.

The musculoperiosteal flaps are then re-approximated and sutured together. The postauricular tissues are closed in layered fashion.

A mastoid pressure dressing is placed.

Previous