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Semicircular canal dehiscence (SCD) syndrome is rare, and its diagnosis is a significant challenge in clinical practice. Our aim was to explore application of the loud sound stimulation test for diagnosing SCD syndrome. Eight cases of superior semicircular canal dehiscence (SSCD), among them two patients had bilateral dehiscences and one case of lateral semicircular canal dehiscence (LSCD). A total of 11 dehiscences were studied retrospectively. Loud sounds (pure tones, 100 dB, 110 dB nHL) at frequencies of 500, 1,000, and 2,000 Hz were used to stimulate both ears for 5 s. A temporal bone computed tomography (CT) scan with semicircular canal reconstruction was performed in all patients. Vertigo was present in seven of nine cases following loud sound stimulation. In addition, the patient with LSCD demonstrated horizontal eye movement following loud sound stimulation, whereas six patients with SSCD showed rotational eye movement. Among them, two patients with bilateral superior canal dehiscence showed a positive response to the loud sound stimulation in only one ear. The diagnoses of all patients were confirmed with a high-resolution temporal bone CT with corresponding multi-planar reconstruction of the affected semicircular canals with various size dehiscences. We conclude that the characteristic eye movement following loud sound stimulation is valuable for diagnosing SCD syndrome. In addition, the loud sound stimulation test has unique advantages, especially for confirming the affected ear and the corresponding semicircular canal. [ABSTRACT FROM AUTHOR]

Dehiscence of the lateral semicircular canal (LSCD) has been reported much but mainly in association with cholesteatoma and canal wall down mastoidectomy, while idiopathic LSCD was rarely reported. Bassim reported one case with lateral semicircular canal dehiscence, but presented no vestibular or auditory symptoms. The patient in this study complained significant sound-induced vertigo and autophony in his right ear. The axis of nystagmus was orthogonal to the lateral semicircular canal, and no torsional or vertical motions were observed, so pathology of the lateral semicircular canal was preferentially considered. Benign paroxysmal positional vertigo was excluded since vertigo attacks had no relation to the change of head position. The dehiscence of the right lateral semicircular canal was then confirmed through the high-resolution temporal bone computer tomography scan and the reconstructed images. The cause of the LSCD is poorly understood, since no history of head trauma, otological infection or surgery was documented. [ABSTRACT FROM AUTHOR]