Superior semicircular canal dehiscence syndrome

Douglas J Lanska MD FAAN MS MSPH (Dr. Lanska of the Great Lakes VA Healthcare System and the University of Wisconsin School of Medicine and Public Health has no relevant financial relationships to disclose.)
Originally released October 1, 2001; last updated February 7, 2017; expires February 7, 2020

This article includes discussion of superior semicircular canal dehiscence syndrome and SSCD. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

The author explains the clinical presentation, pathophysiology, diagnostic work-up, and management of superior semicircular canal dehiscence syndrome.

Key points

 

• The Tullio phenomenon is sound-induced vertigo, nystagmus, or both.

 

• Hennebert sign is pressure-induced vertigo, nystagmus, or both, elicited by insufflation of the external auditory canal.

 

• Typically, in affected patients with superior semicircular canal dehiscence syndrome, there is a several-year history of symptoms that may include sound-induced vertigo (Tullio phenomenon), pressure-induced vertigo (Hennebert sign), or oscillopsia as well as chronic disequilibrium.

 

• Characteristic signs include sound-induced eye movement and head tilt, Valsalva-induced eye movement, Hennebert sign, and postural sway induced by external auditory canal pressure. Other signs can include pulse-synchronous rotatory nystagmus, hyperacusis to bone-conducted sounds, and conductive hearing loss.

 

• Patients with bilateral superior semicircular canal dehiscence may have vertical oscillopsia and impaired vision during locomotion, disequilibrium, spontaneous pulse-synchronous vertical pendular nystagmus, and Valsalva-induced upbeat jerk nystagmus.

 

• Superior semicircular canal dehiscence syndrome is caused by missing bone over the superior aspect of a semicircular canal, creating a third "mobile window" in the bony labyrinth. This may be a developmental abnormality.

 

• High-resolution computed tomography of the temporal bones is usually considered the definitive test for superior semicircular canal dehiscence.

 

• Patients also have lowered vestibular-evoked myogenic potential thresholds and larger vestibular-evoked myogenic potential amplitudes; vestibular-evoked myogenic potential studies are highly sensitive and specific for superior canal dehiscence (although rare patients with posterior canal dehiscence will also have abnormal vestibular-evoked myogenic potentials).

 

• Patients with superior semicircular canal dehiscence and disabling disequilibrium have benefited from surgically plugging or patching (ie, resurfacing or “reroofing”) the dehiscent superior semicircular canal through a middle cranial fossa approach or, more recently, with a less complicated and potentially safer transmastoid approach.

Historical note and terminology

The Tullio phenomenon is sound-induced vertigo, nystagmus, or both. In experiments conducted during the first half of the 20th century, Italian biologist and physiologist Pietro Tullio (1881–1941), Dutch otolaryngologist Eelco Huizinga (1893–1976), AJH van Eunen, and colleagues established that (1) fenestration of individual semicircular canals made pigeons susceptible to sound-evoked eye and head movements in the plane of the fenestrated canals and (2) these responses were transiently abolished by applying cocaine to the ampulla of the fenestrated canal (Tullio 1929; Huizinga 1934;1935; Van Eunen et al 1943; Addams-Williams et al 2014).

Hennebert sign is pressure-induced vertigo, nystagmus, or both elicited by insufflation of the external auditory canal. Belgian otolaryngologist Camille Hennebert (1867–1954) originally reported this phenomenon in syphilitic patients (Hennebert 1911).

Both the Tullio phenomenon and Hennebert sign can occur together in patients (Cawthorne 1956; Erlich and Lawson 1980; Minor et al 1998), presumably because of disruption of the bony labyrinth (Cawthorne 1949; Cawthorne 1956). Examples include erosion of bone of the horizontal semicircular canal by cholesteatoma and surgical fenestration of the horizontal semicircular canal as a treatment for hearing loss in otosclerosis (Minor et al 1998).

Superior semicircular canal dehiscence syndrome is a newly recognized vestibular disorder, first reported by American otolaryngologist Lloyd Minor and colleagues in 1998. Characteristic clinical features of the disorder include both Tullio phenomenon and Hennebert sign (Minor et al 1998; Adams and Levine 2011; Basura et al 2014).

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