Otology Seminar
Superior Semicircular Canal Dehiscence Syndrome
R3 黃俊棋 2006/01/18
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Introduction:
 Henebert sign: (1905) compression and rarefaction of the air in the external
auditory canal in some patients, having intact tympanic membranes, caused
small-amplitude, brief, nystagmic movement of the eyes
 Tullio phenomenon: vertigo or other abnormal vestibular sensations
accompanied by eye and/or head movements in response to sound (1929,
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fenestration of individual semicircular canals in pigeons led to sound
evoked eye and head movements in the plane of these canals)
Minor et al. (1998): vestibular symptoms induced by sound or by changes in
middle ear or intracranial pressure with eye movements align with plane of
dehiscent superior semicircular canal
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Clinical manifestation:
 Vertigo or oscillopsia induced by loud sounds (Tullio phenomenon), by
changes in pressure in the external canal that are transmitted to the middle
ear (Hennebert sign), or by Valsalva maneuvers
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Upward and torsional movement (superior pole of eye on stimulated side
was intortion or nasally, on nonstimulated side was extorsion or temporally)
of both eyes induced by sound or positive pressure
Hyperacusis for bon-conducted sounds like hearing eye movements, pulse
or impact of feet during walking or running
Sound-induced tilt of head in plane of superior canal and chronic
disequilibrium
M:F = 41:19, mean age: 43 y/o (Minor, 2005, 65 cases)
Drop attack (Brantberg et al. 2005, 2 cases)
Spontaneous pulse-synchronous vertical pendular nystagmus due to
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bilateral SCD (Tilikete et al. 2004)
Torsional oscillation of eyes in rhythm with pulse (Minor et al. 2003)
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Diagnosis:
 Audiometry
 Weber test lateralizes to affected ear, seems from lateral malleolus of
ankle
 Rinne test: air conduction > bone conduction
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Bone conduction thresholds can be less than 0 dB (↓5-10 dB) at low
frequency (< 2000 Hz)
ABG: 19 + 14 dB at 250 Hz, 15 + 11 dB at 500 Hz, 11 + 9 dB at 1000
Hz, 4 + 6 dB at 2000 Hz (Minor, 2005, 65 cases)
Intact stapedius reflex, type Ad tympanogram
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Nystagmogram
 Frenzel lenses or 3-D VNG
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Head thrusts
 Deficient VOR evoked by rapid, high-acceleration, transient head
movements in planes of canal because of hypofunction
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VEMP
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Lower threshold for eliciting VEMP response
High amplitude of VEMP response
HRCT
 0.5 mm collimation with helical section, sensitivity: 100%, specificity:
99%, positive predictive value: 93%, negative predictive value: 100%
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2 negative exploration, CT unable to detect bone thinner than 0.1 mm
(Mikulec et al. 2005, 11 cases)
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Etiology:
 Thickness of bone overlying intact superior canal in patients with unilateral
dehiscence is significantly thinner
 Patients were commonly middle aged
 Fail to develop normal thickness of bone overlying superior canal and
disrupted either by traumatic event or eroded over time by pressure from
overlying temporal bone or dura (Minoret al. 1988: 2/8, 2005: 22/65)
 Incidence of dehiscence or thinning (< 0.1mm) by histologic study: 0.7-1 %
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Mechanism:
 Dehiscence creates a third mobile window into the inner ear
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Eye movement
 Shunted volume velocity stimulates ampula of SC
 Loud sounds, positive pressure in EAC or Valsalva maneuver cause
ampullifugal (excitory) deflection of cupula
 Negative pressure in EAC, reverse Valsalva maneuver or jugular
venous compression cause ampullifetal (inhibitory) deflection of
cupula
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Air-conduction
 Animal study with chinchilla showed volume velocity and pressure
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shunting away from cochlea, through the dehiscent canal
Songer & Rosowski 2005: Cochlear potential↓ after introduction of
dehiscence and return after path of dehiscence; pressure at EAC also ↓
Bone-conduction
 Lower cochlear impedance (compression) and decrease load at oval
window (inertia)
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VEMP
 Lower impedance for transmission of sound and pressure through
semicircular canal and larger deflections of vestibular sensors
Differential diagnosis:
 Congenital or acquired syphilis
 Gummatous osteomyelitis and labyrinthine fistula
 No hyperacusis for bon-conducted sounds
 VDRL and TPHA
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Enlarged vestibular aqueduct syndrome
 Usually bilateral and young age
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Family history
Sudden, fluctuating, or progressive sensorineural hearing loss at high
frequency
HRCT finding
Patulous Eustachian tube
 Autophony of breathing sound
 Movement of tympanic membrane on deep nasal inspiration
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Otosclerosis
 Female, bilateral, 20-40 y/o
 Schwartze’s sign
 Carhart’s notch
 Absent stapedius reflex
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Labyrinthine fistula caused by cholesteatoma
 Local findings
 Usually horizontal semicircular canal
 HRCT finding
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Perilymphatic fistula
 Exclusionary criteria
Treatment:
 Avoidance of loud noises may be sufficient prevent clinical manifestation
 Tympanostomy tube for symptoms mainly from pressure in external
auditory canal
 Surgical repair should be reserved for patients who are debilitated by their
symptoms
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Plugging or resurfacing via middle cranial fossa approach
Complete relief of symptoms without recurrence was 7/11 in resurfacing
procedure and 8/9 in plugging procedure (Minor, 2005, 65 cases)
2/20 had post-op hearing loss; one plugging and the other resurfacing;
possible reason include: tearing of membranous canal, chemical
labyrinthitis or secondary endolymphatic hydrops (Minor, 2005, 65 cases)
Complication: 2 with BPPV improved after Epley maneuver, 1 with SD
improved after steroid, 2 with permanent mild high frequency hearing loss
(Mikulec et al. 2005, 11 cases)
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Further developments:
 Why some have exclusively vestibular abnormalities, some exclusively
auditory effects, and others both
 Whether cochlear aqueduct is patent
 Relative compliance of round window membrane
 Size of dehiscence not correlate with severity of symptoms
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References:
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Minor LB, Solomon D, Zinreich JS, Zee DS. Sound- and/or pressure-induced vertigo due
to bone dehiscence of the superior semicircular canal. Arch Otolaryngol Head Neck Surg.
1998 Mar;124(3):249-58.
Minor LB. Clinical manifestations of superior semicircular canal dehiscence.
Laryngoscope. 2005 Oct;115(10):1717-27.
Songer JE, Rosowski JJ. The effect of superior canal dehiscence on cochlear potential in
response to air-conducted stimuli in chinchilla. Hear Res. 2005 Dec;210(1-2):53-62.
Rosowski JJ, Songer JE, Nakajima HH, Brinsko KM, Merchant SN. Clinical, experimental,
and theoretical investigations of the effect of superior semicircular canal dehiscence on
hearing mechanisms. Otol Neurotol. 2004 May;25(3):323-32.
Minor LB. Labyrinthine fistulae: pathobiology and management. Curr Opin Otolaryngol
Head Neck Surg. 2003 Oct;11(5):340-6. Review.
Lempert T, von Brevern M. Episodic vertigo. Curr Opin Neurol. 2005 Feb;18(1):5-9.
Review.
Brantberg K, Ishiyama A, Baloh RW. Drop attacks secondary to superior canal dehiscence
syndrome. Neurology. 2005 Jun 28;64(12):2126-8.
Mikulec AA, Poe DS, McKenna MJ. Operative management of superior semicircular canal
dehiscence. Laryngoscope. 2005 Mar;115(3):501-7.
Schmuziger N, Allum J, Buitrago-Tellez C, Probst R. Incapacitating hypersensitivity to
one's own body sounds due to a dehiscence of bone overlying the superior semicircular
canal. A case report. Eur Arch Otorhinolaryngol. 2006 Jan;263(1):69-74.