Introduction to Superior Canal Dehiscence

Superior Canal Dehiscence, often abbreviated as SCD, is a rare but impactful condition of the inner ear characterized by a thinning or absence of bone over the superior semicircular canal. This creates an abnormal "third window" into the inner ear, allowing sound and pressure waves to enter and exit the labyrinth in an uncontrolled manner. This unusual opening disrupts the normal biomechanics of the inner ear, leading to a wide array of auditory and vestibular symptoms.

Diverse Symptoms of SCD

Individuals with Superior Canal Dehiscence can experience a complex combination of symptoms, often affecting both hearing and balance. Auditory symptoms are distinctive and include autophony, where one can hear their own bodily sounds such as their heartbeat, eye movements, or even chewing with unusual clarity. Some may also report pulsatile tinnitus, a rhythmic buzzing or whooshing sound synchronized with their heartbeat. Increased sensitivity to everyday noises, known as hyperacusis or general sound sensitivity, is common. Patients might experience a conductive hearing loss, particularly in low frequencies, despite normal middle ear function.

Vestibular symptoms are equally disruptive. Many report chronic dizziness and episodes of vertigo, which can be triggered by loud sounds (a phenomenon known as the Tullio phenomenon) or changes in pressure, such as straining, lifting, or even sneezing. This manifests as significant pressure sensitivity. Eye movements can also be affected, with some experiencing sound-induced or pressure-induced nystagmus. General instability and persistent balance issues can severely impact daily life, sometimes accompanied by debilitating headaches.

Diagnosis and Identification

Diagnosing SCD requires a comprehensive approach, combining clinical evaluation with specific diagnostic tests. A thorough review of the patient's unique auditory and vestibular symptoms is paramount. Audiological tests may reveal specific patterns of conductive hearing loss or hypersensitivity to sound. Vestibular tests, such as Vestibular Evoked Myogenic Potentials (VEMPs) and evaluations of acoustic reflexes, can often show abnormalities indicative of a third window lesion, demonstrating a lower threshold for activation than in healthy individuals.

The definitive diagnosis of Superior Canal Dehiscence is confirmed through imaging. A high-resolution CT scan of the temporal bones is the gold standard, clearly showing the dehiscence or opening in the bone overlying the superior semicircular canal. Specialized imaging protocols are often used to ensure the precise identification of the defect without artifact.

Treatment Approaches for SCD

For individuals significantly impacted by SCD, surgical intervention is typically the most effective treatment. The primary goal of surgery is to close or reinforce the dehiscent area, thereby eliminating the "third window" effect. There are several surgical approaches, predominantly via a middle fossa craniotomy or a transmastoid approach.

• Resurfacing: This technique involves covering the dehiscent area with bone cement or bone graft to restore the normal bony integrity over the superior canal.
• Plugging: This method involves directly plugging the superior semicircular canal with bone chips, fascia, or tissue, effectively closing off the abnormal opening.

During these procedures, meticulous care is taken to avoid complications, including careful management of any generated bone dust. Post-operative recovery can vary, but many patients experience significant relief from their distressing auditory and vestibular symptoms, leading to an improved quality of life.