[Three-dimensional characteristics of torsional nystagmus in induced by posterior semicircular canals canalithasis].

Objective:The three-dimensional direction feature of torsional nystagmus induced by posterior semicircular canal canalithasis （PSC-Can） was recorded and analyzed using three-dimensional video nystagmography （3D-VNG）. Methods:Sixty patients （22 on the left side and 38 on the right side） with PSC-Can were enrolled for torsional nystagmus evoked by Dix-Hallpike test in the affected-side head-hanging and sitting positions, and the direction characteristics of the horizontal, vertical and torsional components were analyzed. Results:Vertical torsional nystagmus was induced in 60 PSC-Can patients in the head-hanging and sitting positions evoked by Dix-Hallpike test, respectively. Horizontal, vertical, and torsional components of were presented in the 3D-VNG. In the head-hanging position, the direction of horizontal component in the left/right PSC-Can nystagmus was contralateral in 46 cases（the other 14 cases were ipsilateral）, the vertical component was upward, and the torsional component was upward/downward, respectively. The intensity of nystagmus induced in the three components in the sitting position is weaker than in the head-hanging position, and the direction of nystagmus was reversed in both vertical and torsional components compared with the head-hanging position. However, the direction of the horizontal component was reversed in 39 cases and not reversed in 21 cases in the sitting position. Conclusion:The horizontal, vertical and torsional components of the torsional nystagmus in PSC-Can patients recorded by 3D-VNG, which provided more comprehensive and objective information for the analysis of PSC-Can and the study of semicircular canal physiological function.