Endoscopic‐assisted repair of superior canal dehiscence syndrome

Superior canal dehiscence syndrome (SCDS) was first characterized by Minor et al. as a bony defect of the superior semicircular canal resulting in vestibular and auditory dysfunction. The etiology of superior canal dehiscence (SCD) is not completely understood, though some suggest it may be associated with a congenitally thin or absent bony covering. In some cases it is made symptomatic by a second event, such as a closed head injury or acute change in cerebrospinal fluid (CSF) pressure. Depending on the age of the patient and severity of symptoms, treatment can be conservative (e.g., interval audiometric testing, avoidance of provocative stimuli) or surgical (e.g., direct or indirect isolation of the bony defect via middle fossa craniotomy or transmastoid approach). Minor et al. initially presented the middle fossa craniotomy approach to repair an arcuate eminence defect in 1998. It is now the most commonly reported surgical technique, and its success is well established. Advantages of the middle fossa craniotomy include 1) direct access to the arcuate eminence defect without the need for labyrinthine bone removal and 2) exposure of the surrounding skull base to repair associated tegmen defects or encephalocele. The middle fossa craniotomy is also ideal for SCDS patients with a lowlying tegmen, as this method allows for wide exposure of the arcuate eminence without drilling close to the horizontal canal. The transmastoid technique avoids a craniotomy and brain retraction and is connected with lower morbidity and hospital stay. Transmastoid repairs have also been associated with tegmen defects and dural injury, which can result in a CSF leak or delayed encephalocele formation postoperatively. At our institution, we prefer the transmastoid approach in SCD cases involving the superior petrosal sinus to address a medial defect of the nonampullated end and in certain revision cases. One of the limitations of a middle fossa craniotomy is exposure of the medial skull base and the risks of temporal lobe retraction. When an arcuate eminence defect is very thin (“blue-lined”) or falls along a downsloping tegmen, it can be difficult or impossible to visualize without significant retraction or drilling of the overlying skull base (Fig. 1). Excess retraction can lead to dural tears, CSF leak, or brain contusion. The additional extradural dissection needed to fully expose a medial superior canal defect can also increase the risk of facial nerve injury. The geniculate ganglion has been found to be dehiscent in up to 38.1% cases of SCD and is vulnerable to injury if more anteromedial exposure is needed. Due to several challenges with poor visualization of the SCD defect and prolonged temporal lobe retraction in craniotomies using binocular microscopy at our institution, we wanted to determine if an angled, rigid endoscope would assist in these special cases. Although there were no long-term complications associated with these surgeries, we believe that our standard approach was suboptimal. Better visualization would improve the safety and efficacy of the procedure. The use of a 0 endoscope during middle fossa craniotomy for SCD repair was mentioned in a poster presentation by Shaia et al. In the following report, we describe the use of 30 endoscopy in five patients with SCDS who underwent repair via middle fossa craniotomy. We hypothesize that skull base endoscopy is a safe and effective way to identify and repair a medial or From the Department of Otolaryngology (M.S.C., S.L., D.J.L.), Massachusetts Eye and Ear Infirmary, Boston; Department of Otology and Laryngology (M.S.C., S.L., D.J.L.), Harvard Medical School, Boston, Massachusetts, U.S.A. Editor’s Note: This Manuscript was accepted for publication November 8, 2013.