Superior Semicircular Canal Superior Semicircular Dehiscence Canal Anatomy and Deborah Farragher, Judith White Physiology Section of Vestibular and Balance Disorders

Superior semicircular canal dehiscence SSCD (SSCD) syndrome Positive pressure in the external auditory canal • First described by Minor et al 1998 and Valsalva against pinched nostril causes • Sound or pressure induced eye upwards slow phase nystagmus directed away movements from the affected ear. • Defect in the bone overlying the SCC Negative pressure in the external canal and Valsalva against a closed glottis cause slow forms an abnormal connection between phase nystagmus downwards and towards the the and intracranial affected ear. compartment. Fixation will suppress the nystagmus, and videonystagmography is helpful.

Eye movements align SSCD with the abnormal canal • Tonic upwards and ipsilateral intorsion is seen with ampullofugal endolymph • Positive middle flow - activation (loud noise, positive ear pressure or middle ear pressure) loud sound stimulates • Tonic downwards and ipsilateral ampullofugal extorsion is seen with ampullopetal endolymph flow - endolymph flow - inhibition (Valsalva canal activation against a closed glottis, jugular • Eye movements compression, raised intracranial are tonic upwards pressure) with ipsilateral intorsion.

1 SSCD SSCD

• Hypothesis: vibration acts on the • Valsalva against a bony dehiscence when applied in a cranio-caudal direction to set up closed glottis or bidirectional superior semicircular jugular compression canal endolymph flow and cause the characteristic torsional causes increased nystagmus. intracranial pressure • Are the otolith organs ( and utricle) involved in the response, and ampullopetal particularly in bilateral cases where endolymph flow - vertical nystagmus is seen? canal inhibition • Eye movements are tonic downwards with ipsilateral extorsion

Proposed Mechanism Physical Exam

• Loud tones in left ear showed nystagmus with vertical and torsional components

Tullio Phenomenon

• Initially described by Tullio based on experiments in animals where the bone was Symptoms Associated fenestrated overlying the semicircular canal and eye and head movement were evoked in with SSCD the plane of the canal with loud noise (Alexander’s law) . Later used to describe findings seen in patients with syphilitic erosion of the labyrinth or advanced Meniere’s with labyrinthine adhesions. • Test at 2000 Hz at 110 dB

2 Typical presenting symptoms Common Presenting complaints • Chronic disequilibrium (76 %) • Sound induced disequilibrium • Sound evoked disequilibrium or visual – Loud noises cause imbalance or frank instability vertigo • Pressure evoked disequilibrium or visual • Organ music • Fire alarm instability • School bells (teachers) • Conductive hyperacusis (unusually sensitive • Loud telephone or music to vibration) 39% • Audiologist (demonstrating audiologic screening on herself)

Common Presenting Common Presenting Symptoms Symptoms • Pressure Induced Disequilibrium • Loss – Elevators – Muffled, blocked or echo in hearing – Scuba Diver – Usually low frequency – Sneezing – Typically reduced hearing for sounds presented thru the air, but unusually sensitive hearing for – Flying sounds presented via vibration () – Straining – Patient may hear a vibrating tuning fork applied to – Lifting Weights their ankle in their ear (conducts vibration thru skeleton)

Less Common Associated Symptoms Case Descriptions • Hearing Eyes Move 47 yowith a 10 yr. hx. of gradually • Hearing Heartbeat worsening vertigo and oscillopsia induced by • Hearing other usually imperceptible loud noises, lifting or straining. physiologic sounds (breathing, blood flow, joint movement) Audiogram showed a low frequency 20-30 • Visual instability with running, walking dB conductive hearing loss with bone • Atypical Positional Vertigo (minimal thresholds at –5 to –15 dB. prolonged torsion in ear down positions) – Dura may pull on canal

3 More Cases More Cases

• 36 yo with oscillopsia with loud noises or • 62 yo male intolerant to supine positions tragal pressure/Valsalva. Constant and pressure changes for 1 year. Prior disequilibrium. s/p stapedectomy for outside audiogram did not test bone presumed otosclerosis (20-25 dB CHL, no conduction. MRI negative. benefit from surgery). • Vestibular physical therapy with • CT confirmed SSCD repositioning unsuccessful. • CT obtained, which showed large left superior semicircular canal dehiscence.

More Cases More Cases

• 50 yo male seen in consultation from • 76 yo female with gait problems and neurology. Complains of pulsatile tinnitus frequent falls. Prior canal wall down right ear and lightheadedness, disequilibrium with loud noise, clearing ears or pressure mastoid surgery right, age 17. Right ear changes. Very difficult to work as a always sensitive to cold wind. MRI machinist. Having difficulty driving Harley normal. Davidson. • Audiogram showed conductive hearing • Audiogram showed characteristic low frequency conductive hearing loss right ear, loss right ear (likely secondary to prior with normal acoustic reflexes. mastoid surgery). • CT confirmed large right SSCD • CT showed right SSCD

More Cases More Cases

• 74 yo male with positional vertigo rolling to • 42 yo male professional scuba diver right and on awakening, frequent falls, poor complaining of severe vertigo with pressure balance. equalization • Vestibular physical therapy and repositioning • Audiogram suggested low frequency maneuvers not successful conductive hearing loss bilaterally • Right torsional nystagmus in right ear down positioning, with persistent atypical positional • Vestibular testing normal nystagmus following 11 trials of repositioning • CT showed bilateral SSCD, larger on the left • No tinnitus or hearing change. Audiogram • Patient elected to continue diving against normal for age. MRI normal. . medical advice • Bilateral SSCD on CT

4 THE HISTORY

• History is the most sensitive, useful and valuable test in diagnosing this disorder. Diagnostic Tools • ASK about noise sensitivity, pressure sensitivity and hearing loss.

NEXT TEST: AUDIOGRAM Audiologic Analysis

• Look for bone conduction hearing above • Left ear low frequency conductive hearing average, with low frequency reduced loss hearing for other sounds – low frequency conductive hearing loss. Affects 39% of patients with SSCD. • Normal acoustic reflexes (these will be absent in other forms of conductive hearing loss, including otosclerosis and middle ear disease)

Audiogram

5 Vestibular Evoked Recommendations for Myogenic Potential - VEMP Audiologists • Test • For audiograms suggesting conductive • Applies loud sound to the ear hearing loss with normal tympanograms , • Triggers relaxation of a contracting consider VEMP testing. VEMP will be sternocleidomastoid muscle thru a absent in conductive hearing loss due to reflex (saccule-brainstem-motor nerve) otolscelrosis or ossicularproblems, but • Unusually active in SSCD present in SSCD. Also consider testing for • A useful screening test bone thresholds above 0 dB in this group. • May be false negative if patient cannot SSCD is associated with supra -normal bone tense neck, but rarely false positive thresholds (conductive hyperacusis ).

Imaging Radiological Correlates

• High resolution • High resolution CT in plane of the canal temporal bone CT- • Radiographically present in 20% of imaging scan showed studies dehiscence overlying left • Histologically present in 10% of temporal superior bones semicircular canal. • Greater than 5 mm in size, dural compression causes loss of superior canal function.

Vibration-induced Vibration protocol nystagmus Useful office procedure to screen for SSCD, uses vibration applied to base of skull while observing nystagmus (Frenzel lenses helpful)

6 Signs and Findings in SSCD • Low frequency conductive hearing loss with supra-threshold bone conduction Treatment Options In • Low threshold of vestibular evoked SSCD myogenic potential (VEMP) • CT temporal bones with fine cuts reconstructed in the plane of the superior semicircular canal demonstrate bony dehiscence between the top of the canal and the middle cranial fossa

Treatment Options in SSCD Disabling Symptoms

• Diagnosis itself is very reassuring to • Pressure Equalizing tubes may help patients • Treatment of co-morbid exacerbating • Watchful waiting is a good management conditions such as migraine is very strategy. Symptoms often improve as helpful dehiscence expands.

Disabling Symptoms Pearls

• Benzodiazepines are not indicated for • Dehiscence is often bilateral, since skull the long term management of vestibular shape is usually symmetric disorders • Other canals may be dehiscent, with • Superior Canal Plugging similar presenting symptoms – Middle cranial fossa or trans mastoid – Mastoid surgery may thin lateral canal procedure with low risk of hearing loss or – Posterior canal dehiscence is possible, but vestibular ablation in experienced hands less frequent

7 Questions THANK YOU

References

Cremer P.D. et al. Eye movements in patients with superior canal dehiscence syndrome align with the abnormal canal.. Neurology Dec 2000 1833 -1841

Minor, L. et al. Sound and pressure-induced vertigo due to bone dehiscence of the superior semicircu lar canal. Arch Otol. HNS Mar 1999 249 -258.

Gianoli, G. Deficiency of the superior semicircular canal. Current op inion in otolaryngology 2001 1 -6.

Minor, L. Superior canal dehiscence syndrome. Am. J. Otol. 21, 2000 9 -19.

Hirvonen , T. et al. Superior Canal Dehiscence. Arch Oto HNS 127 2001 1331 -1336.

Rosowski, J. Clinical, experimental and theoretical investigations of the effect of the superior semicircular canal dehiscence on hearing mechanisms. Otoland Neurotol. 25, 2004 -323-332.

Streubel, S. et al. Vestibular -evoked myogenic potentials in the diagnosis of superior canal dehiscence syndro me. Acta Otolaryngol545 2001 41 -49.

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