Tullio phenomenon with dehiscence of the superior semicircular canal

Hypothesis: The goal of the investigation was to determine if vector analys is of nystagmus in a patient with the Tullio phenomenon could determine the source of the nystagmus. Background: The Tullio phenomenon consists of the combination of vertigo an d abnormal eye and/or head movements provoked by sound. Dehiscence of the s uperior semicircular canal can be found in certain patients with the Tullio phenomenon. Methods: The patient was tested with pure tones ranging from 250 to 3000 Hz at 95dB HL. The time course of the three-dimensional vector of eye movemen t. including torsion and vertical and horizontal displacement angles was de termined by individual stop-frame analysis of digitized video. Results: Torsion amplitude varied from 1 to 7 degrees; vertical amplitude v aried from 1 to 5 degrees; and horizontal amplitude varied less than 1.5 de grees. The maximal response occurred on stimulation of the right ear with a 1250-Hz 95-dB HL tone. This elicited a reliable counterclockwise torsional and down-beating fast phase nystagmus as seen from the examiner's point of view. Comparison of the nystagmus with known canal vectors identified the right superior semicircular canal as the sourer of stimulation. High-resolu tion computed tomography scan of the temporal hone showed a definite right superior canal dehiscence. Conclusion: The origin of nystagmus from the Tullio phenomenon can be ident ified by calculating the three-dimensional vector of the observed nystagmus . We show that vector analysis of the observed eye movement can be used to infer the source of nystagmus in these patients. The development of real-ti me, three-dimensional vector analysis of nystagmus is desirable.