Surgical Treatment of Superior Semicircular Canal Dehiscence Syndrome

Abstract

Superior semicircular canal dehiscence syndrome (SCDS) is a clinical entity resulting in a myriad of audiological and vestibular symptoms. Pressure and/or sound-induced vertigo/nystagmus, autophony, conductive hearing loss, and conductive hyperacusis are commonly seen in patients with SCDS. The physiologic mechanism of this syndrome is thought to be due to the dehiscence creating a low-impedance outlet for fluid waves in the labyrinth, commonly referred to as a third window. This shunts flow from the cochlea to the labyrinth, which both activates the vestibular system and decreases pressure driving the traveling fluid wave in the cochlea. Diagnosis of SCDS can be difficult and requires both radiographic evidence of a dehiscence and clinical evidence supporting SCDS as the etiology for a patient’s symptoms. Testing for SCDS includes high-resolution CT imaging, audiogram, cervical and ocular VEMP testing, head impulse testing, and visualization of sound- or pressure-induced eye movements in the plane of the affected superior canal. Traditional surgical repair of SCDS is via the middle fossa approach. This approach allows for the dehiscence to be seen directly and for it to be both plugged and resurfaced. This approach is preferred in the vast majority of patients, but in certain situations a transmastoid approach can offer benefits over the middle fossa approach. Surgical outcomes for repair of SCDS are quite favorable, with patients having improvement of autophony, imbalance, and vertigo. Patients with predominately audiological symptoms have the highest likelihood of postoperative improvement. The majority of patients report an improvement in their quality of life postoperatively. Complications are rare but do occur in both the middle fossa and transmastoid approaches to SCDS repair. The most common complication is hearing loss, which is typically mild but can be profound in a low percentage of patients. The importance of proper patient selection and preoperative counseling on the risks of surgery cannot be overstated to ensure good surgical outcomes in SCDS repair.