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Fascia with Bone Pate Resurfacing Technique for Repair of Superior Semicircular Canal Dehiscence

Contributors: Jacob B. Hunter, Reid C. Thompson and David S. Haynes

Superior semicircular canal dehiscence (SCD) is a condition in which the bone overlying the superior semicircular canal is absent. The clinical presentation of SCD is highly variable and may include both auditory and vestibular manifestations. The more common symptoms include autophony, sound or pressure induced vertigo, hypersensitivity to sound, and low frequency conductive hearing loss. Repair can be accomplished via either transmastoid or middle fossa approaches, with numerous materials used to either plug or resurface the canal. Herein, we describe our resurfacing technique using a loose areolar tissue-bone pâté-loose areolar tissue sandwich through a middle fossa approach.

DOI#: http://dx.doi.org/10.17797/kcwvab3b7r

A lazy-S incision is centered above the posterior external auditory canal on the temporal line; inferiorly it curves 0.5 cm posterior to the auricular sulcus, while superior it curves posterior to the temporal hair tuft. Hair is shaved along the incision line, preserving the temporal hair line. The incision is made with a 15 blade, and dissection proceeds to the level of the loose areolar tissue overlying the true temporalis fascia. A large piece of the loose areolar tissue is harvested and allowed to dry. Self-retaining retractors are placed and the temporalis muscle is incised with electrocautery along the temporal line. The musculoperiosteal flap is elevated and the external auditory canal is clearly identified. The temporalis muscle is then incised vertically to expose the temporal squama. A small craniotomy, roughly 4 X 2 cm, is designed and centered on the posterior aspect of the external auditory canal. While drilling the craniotomy, bone p���¢t���© is harvested using a freer elevator and allowed to dry. The temporal lobe is then elevated extradurally, working in posterior to anterior fashion to minimize the risk of traction injury to the geniculate ganglion. A cotton pledget is placed at the end of the suction to minimize direct manipulation of the membranous superior semicircular canal prior to its definitive identification. Once the SCD is identified (see below for anatomy/landmarks), dura is elevated circumferentially around the dehiscence to at least the posterior petrous ridge. Repair is then undertaken via resurfacing the SCD. Initially, a piece of the previously harvested loose areolar tissue is placed over the SCD. Bone p���¢t���© is then placed on top of the loose areolar tissue, covering the entirety of the initial graft. A second piece of loose areolar tissue is then placed to sandwich the bone p���¢t���© between both grafts. The dura is then gently laid back into place. The bone flap is replaced, and the incision is closed in multi-layered fashion. A head wrap is placed.
Patients with symptomatic SCD not controlled with conservative measures are candidates for repair.
Bleeding disorders should be optimized prior to surgery and patients should hold all anticoagulant medications for at least 1 week prior to surgery.
The patient is positioned in the park bench position and the head is placed in a Mayfield skull clamp.
The diagnosis of SCD is made radiographically, therefore all patients should undergo fine cut temporal bone computed tomography (CT) imaging. In addition, a complete history, physical examination and routine audiometric testing should be performed. While balance function testing is not required, we recommend such testing particularly in patients with vestibular complaints. Vestibular evoked myogenic potentials (VEMPs) can aid in the diagnosis of SCD.
In the coronal plane, the superior semicircular canal is usually located at the level of the posterior external auditory canal. Along the middle fossa floor, the superior semicircular canal is oriented perpendicularly to the posterior petrous ridge. Although the arcuate eminence corresponds to the location of the superior semicircular canal in the majority of patients, this relationship is not absolute. Furthermore, in patients with SCD, the arcuate eminence will likely not be as prominent. In relation to the lateral cortex of the temporal squama, the superior semicircular canal lies roughly 2.5 cm medially.
Advantages: We feel the use of loose areolar tissue, bone p���¢t���©, and loose areolar tissue resurfacing allows the material to conform to the structure of the middle fossa floor. This facilitates obtaining complete resurfacing of the SCD and contrasts with resurfacing techniques that used rigid materials such as cartilage or bone. Further, concomitant tegmen defects, which are not uncommon in patients with SCD, can be repaired simultaneously with the described approach. Disadvantages: Risk of undergoing a middle fossa craniotomy.
Risks include bleeding, infection, hearing loss, spinal fluid leak, dizziness, facial nerve weakness, change in taste, aphasia, stroke, and death.
Risks include bleeding, infection, hearing loss, spinal fluid leak, dizziness, facial nerve weakness, change in taste, aphasia, stroke, and death.
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