Superior Semicircular Canal Dehiscence

Superior semicircular canal dehiscence (SSCD) is a recently identified medical condition first described by Lloyd Minor in 1998. It affects the inner ear, leading to issues with hearing and balance. SSCD occurs due to a defect in the bony structure of the superior semicircular canal, creating an abnormal opening (or “window”) between the inner ear and the middle cranial fossa. This opening disrupts the normal function of the inner ear and leads to a range of symptoms.

Symptoms

The symptoms of SSCD can vary based on the size of the bony defect. Larger defects often result in both hearing and balance problems, while smaller defects might only cause one set of symptoms. Common symptoms include:

• Hearing Loss: Typically involves low-frequency conductive hearing loss.
• Extreme Sensitivity to Sound: Patients may hear internal body noises, like their own footsteps or even eye movements. This enhanced bone conduction can also cause them to hear a tuning fork placed on their elbow.
• Autophony (or Tympanophony): Hearing their own voice echoing inside their head.
• Vertigo and Imbalance: Triggered by loud sounds (known as Tullio’s phenomenon) or activities like straining.
• Pulsatile Tinnitus: A sensation of hearing one’s heartbeat in the ear.

Physiology

The inner ear is a closed system of fluid-filled canals designed to help with hearing and balance. Normally, this system has two functional “windows”:

1. Oval Window: Transfers sound waves from the stapes bone to the inner ear, stimulating hearing.
2. Round Window: Relieves sound wave pressure by directing it from the inner ear to the middle ear.

In SSCD, an abnormal third window forms in the superior semicircular canal. This defect causes sound energy to leak from the hearing system to the balance system. As a result, loud sounds can stimulate the balance system, causing vertigo and instability. The increased compliance (or flexibility) of the inner ear contributes to these symptoms.

Diagnosis

Accurate diagnosis of SSCD involves a combination of tests:

1. Videonystagmography (VNG): Detects abnormal eye movements (nystagmus) during specific maneuvers, such as the Valsalva maneuver. The nystagmus is usually vertical and may include a twisting component.
2. Audiometry: Reveals low-frequency conductive hearing loss with better-than-normal bone conduction levels.
3. Tympanometry: May show dizziness when pressure is applied, and the presence of stapedial reflexes even with conductive hearing loss.
4. Vestibular Evoked Myogenic Potential (VEMP): Shows a lowered threshold, a hallmark of SSCD.
5. High-Resolution CT (HRCT) Scan: Confirms the presence of a bony defect. Specialized imaging planes (Pörschl’s and Stenver’s) with very thin slices (0.5 mm) ensure small defects are not missed.

Treatment

Treatment options depend on the severity of symptoms and patient preferences:

• Conservative Management:

• • Many patients find relief in simply understanding their condition and its symptoms.
  • Lifestyle modifications and reassurance can help manage mild cases.

• Surgical Intervention:

• • Surgery involves closing the defect in the superior semicircular canal to eliminate the “third window” effect.
  • Approaches:

1. 1. 1. Mastoid Approach: Involves accessing the canal through the mastoid bone. This approach is more commonly used but carries a slight risk of hearing loss.
      2. Middle Fossa Approach: Involves accessing the canal from above, which can preserve hearing but requires specialized surgical expertise.

Both surgical approaches aim to seal the defect and alleviate symptoms. The choice of surgery depends on the patient’s anatomy, symptom severity, and surgeon expertise. SSCD is a treatable condition, and understanding the symptoms and treatment options can significantly improve patients’ quality of life. If you suspect you have SSCD, consult an ENT specialist or otologist for proper evaluation and guidance.