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

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）. 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. 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. 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.