Superior Semicircular Canal Dehiscence (SSCD) is a rare inner ear condition characterized by an abnormal opening or thinning of the bone covering the superior semicircular canal. This creates an unusual pathway within the inner ear, allowing for abnormal transmission of sound and pressure changes, leading to a variety of auditory and balance-related symptoms.
The Anatomy and the Anomaly
The inner ear houses a system responsible for both hearing and balance, including three fluid-filled semicircular canals: the superior (or anterior), lateral, and posterior. Encased in dense bone, these canals detect head movements and maintain spatial orientation. Fluid within them shifts with head motion, sending signals to the brain to regulate balance and stabilize vision.
In SSCD, the bony enclosure over the superior semicircular canal is compromised. This dehiscence, an absence or abnormal thinning of bone, creates a “third window” in the inner ear, disrupting its normal mechanics. This makes the inner ear unusually sensitive to sound and pressure changes, causing characteristic symptoms.
Common Indicators
Individuals with SSCD often experience a range of auditory and vestibular symptoms. A frequently reported symptom is autophony, where a person hears their own internal body sounds with unusual loudness. This can include their voice, heartbeat, the movement of their eyes, or even the sound of their joints.
Another characteristic indicator is the Tullio phenomenon, which involves dizziness, vertigo, or involuntary eye movements (nystagmus) triggered by loud sounds. Pressure-induced vertigo is also common, where activities that alter intracranial or middle ear pressure, such as straining, coughing, sneezing, or lifting heavy objects, can provoke dizziness or imbalance. Some individuals also report conductive hyperacusis, an increased sensitivity to internal bodily noises. Additionally, pulsatile tinnitus, described as a rhythmic whooshing or thumping sound synchronized with one’s own heartbeat, can also occur.
Identifying the Condition
Diagnosing Superior Semicircular Canal Dehiscence typically involves a comprehensive evaluation that combines a detailed review of the patient’s symptoms, a physical examination, and specialized diagnostic tests. The initial assessment helps determine if the reported symptoms align with those characteristic of SSCD.
A high-resolution computed tomography (CT) scan of the temporal bones is a primary diagnostic tool. This imaging technique provides detailed cross-sectional views, allowing clinicians to visualize the bone dehiscence or thinning over the superior semicircular canal.
Vestibular Evoked Myogenic Potentials (VEMPs) are also crucial, measuring the inner ear’s response to sound. Both cervical VEMPs (cVEMPs) and ocular VEMPs (oVEMPs) can detect the hypersensitivity of the dehiscent canal to sound. Audiometry, or hearing tests, may reveal a low-frequency conductive hearing loss, even in the absence of middle ear issues, which is attributed to the “third window” effect where sound energy is abnormally diverted.
Management and Treatment Options
The management of Superior Semicircular Canal Dehiscence can involve both conservative approaches and surgical interventions, depending on the severity of symptoms and their impact on a person’s quality of life. For individuals with mild symptoms, conservative management is often the initial strategy. This includes lifestyle modifications, such as avoiding known triggers like loud sounds or activities that cause pressure changes, to minimize symptom provocation.
When symptoms are debilitating or significantly interfere with daily activities, surgical intervention may be considered. The primary goal of surgery is to close the abnormal opening and restore normal inner ear mechanics, thereby alleviating symptoms.
One common surgical technique is the middle fossa craniotomy, which involves accessing the superior semicircular canal from above, through an opening in the skull. In this procedure, the dehiscent bone can be resurfaced or the canal can be plugged to seal the opening. Another surgical option is the transmastoid approach, which is considered less invasive. This technique involves accessing the canal through the mastoid bone behind the ear, where the canal is typically plugged. While both approaches aim to resolve symptoms, the choice of technique depends on various factors, including the specific anatomical presentation of the dehiscence and patient considerations.