Superior Semicircular Canal Dehiscence Syndrome

Abstract

Superior canal dehiscence syndrome (SCDS) is a vestibular disorder caused by a pathologic third window into the labyrinth that can present with autophony, sound- or pressure-induced vertigo, and chronic disequilibrium among other vestibulocochlear symptoms. Careful history taking and examination in conjunction with appropriate diagnostic testing can accurately diagnose the syndrome. Key examination techniques include fixation-suppressed ocular motor examination investigating for sound- or pressure-induced eye movements in the plane of the semicircular canal. Audiometry, vestibular evoked myogenic potentials, and computed tomography confirm the diagnosis. Corrective surgical techniques can be curative, but many patients find their symptoms are not severe enough to undergo surgery. Although a primarily peripheral vestibular disorder, as first-line consultants for most dizziness complaints, neurologists will serve their patients well by understanding SCDS and its role in the differential diagnosis of vestibular disorders.

Seltene Erkrankungen des vestibulären Labyrinths: von Zebras, Chamäleons und Wölfen im Schafspelz

“…Chronic vestibular hypofunction The following findings indicate chronic uni-or bilateral vestibular hypofunction in EVA: caloric paresis of the affected horizontal semicircular canal, a reduced vHIT gain and refixation saccades for the semicircular canals of the affected labyrinth [211,219,222], vibration-induced nystagmus beating towards the ear with better vestibular function [205], or reduced VEMP amplitudes on the affected side [213]. Association with vestibular migraine Finally, an association of EVA with (vestibular) migraine has been described [205,219] similar to SCD [142,177]. Vestibular hypersensitivity due to the additional third window may be a trigger for migraine symptoms under these circumstances.…”

“…So kann ▶tab. 1 Provokationsmanöver für Syndrome des dritten Fensters und Nystagmusbefunde am Beispiel einer Dehiszenz des linken superioren ( = anterioren) Bogenganges (nach [142]).…”

“…Inner-ear conductive hearing loss Part of the air-conducted sound energy is shunted away from the cochlea to the third window, resulting in a decreased pressure gradient between the oval and the round window, and thus decreased basilar membrane motion. Hence, stereocilia of cochlear hair cells are less deflected, ▶table 1 Clinical tests for third-window syndromes and characteristic nystagmus findings as observed in left superior canal dehiscence (SCD), according to [142] test results Nystagmus…”

“…Around half of the patients presenting for surgical closure of the dehiscence (see Chapter 3.2.2.4) show a positive Hennebertʼs sign (vertigo and nystagmus triggerd by tragus compression) [157] (▶ table 1). Most patients display nystagmus during Valsalva maneuvers and / or presentation of loud pure tones (125-4000 Hz, 110 dB nHL) to the affected ear via headphones (Tullio phenomenon) [142]. ▶table 1 summarizes the resulting nystagmus directions according to Ewaldʼs laws.…”

Biomechanics of Third Window Syndrome

“…Patients with mild symptoms can reduce exposure to loud sounds and avoid physical straining, and those with pressure sensitivity can benefit from a tympanostomy tube (22). Patients with debilitating symptoms are candidates for surgical repair, and about one-third elect to have surgery (70). Canal plugging achieves long-term control more often than resurfacing and is usually the procedure of choice (22).…”