Superior Canal Dehiscence

  

Superior Canal Dehiscence Surgery More Info Link  

 

This a transcript of my Powerpoint Slide Lecture given to a PA Academy conference:

 

History

1929 Tullio first described sound-induced nystagmus in pigeons eye movements in response to loud noises - Tullio’s phenomenon.

1911 Hennebert: eye movements evoked with pressure in the external auditory canals in congenital syphilis patients

Nadol: speculated re: adhesions between the foot plate and saccule

1998 Dr. Minor: described superior canal dehiscence syndrome.

The Typical Signs

Vertigo and oscillopsia evoked by sounds.

Sound induced vertigo occurs in about 97%

Activities that change middle ear intracranial pressure cause vertigo in approximately 82% of patients.

Chronic disequilibrium

Hyperacusis was found at 39% of patients

Evoked Nystagmus

Eye movements in the plane of the superior canal evoked by sounds in 89%

Evoked by valsalva maneuvers in 82%

Tragal pressure in 54%.

21% of patients showed head movements evoked by sounds.

Sensitivity to Bone Conduction

Hearing their joints moving,

Hearing their eye movements

Hearing their heart beat

Hearing their heels strike during walking

Hear a tuning fork placed at a distal extremity.

Physical Examination

Spontaneous nystagmus is generally not appreciated. Subtle evoked nystagmus is common

Use frenzel or IRV goggles

Pneumatic otoscopy and valsalva maneuvers may produce the nystagmus.

Weber: is usually to the affected side

Rinne: tuning fork test: BC >AC

Hear a tuning fork placed on the extremity

Objective Evaluations Include

VEMP

Radiology

Vestibular-Evoked Myogenic Potential Testing (VEMP)

Based on the fact that the saccule is actually sensitive to sound

Useful for detecting abnormal sensitivity to otoliths to sound.

Equipment:

Evoked response computer

Sound generator

Surface electrodes to pick up neck muscle activation

Short latency relaxation potentials in the sternocleidomastoid muscle.

Audiologic Findings

Decreased bone conduction threshold.

Conductive hearing loss: due to dissipation of sound energy due to the third window effect.

Intact acoustic reflexes could help differentiate otosclerosis from superior canal dehiscence syndrome.

Treatment

Varies in corresponding to the severity of symptoms

Education

Identify and avoid aggravating factors -- might be able to avoid surgery

Pressure equalization tube may relieve symptoms of disequilibrium and unsteadiness, especially in patients with concurrent eustachian tube dysfunction.

Surgical Treatment

Superior Canal Resurfacing vs. Canal plugging (as in cases of intractable benign positional vertigo.)

Middle cranial fossa approach vs. Transmastoid approach

Possible loss of vestibular function

Possible sensorineural hearing loss

A plug composed of fascia and bone dust

Superior Canal Resurfacing

Preserves the physiologic function of the semicircular canal

Fascia is placed over the dehiscence

Tucked under the edge of the bone

Bone graft

Fascia again

Fibrin glue

Potential Pitfalls

This technique may also result in vestibular hypofunction.

Bone graft may resorb with time.

Fascia or the bone graft could slip out of place

Return of symptoms

Conclusion

Superior canal dehiscence syndrome is characterized by pressure and/or sound-induced vertigo.

Physical exam findings include pressure-induced nystagmus, localization of Weber tuning fork test and vertigo with sound.

This entity is diagnosed with clinical findings and confirmed by CT scan or other objective testing.