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Objective: In this retrospective study, the aim of the authors was to examine the frequency of involvement of the individual semicircular canals (SCCs) in vestibular neuritis (VN) and to assess the degree of long-term recovery. A secondary aim was to retrospectively determine the usefulness of a three-step bedside oculomotor test (the HINTS-test) for the differential diagnosis of peripheral VN.Methods: 44 cases were evaluated during the acute phase and approximately two months later. The gain of the vestibuloocular reflex was determined using video-head-impulse test, carried out using Otometrics ICS Impulse Otosuite Vestibular V 1.2.Results: In 19 cases (43%), a typical, so called "superior" VN could be diagnosed; in 17 cases (38%), all three SCCs were involved; in 4 cases, an isolated inferior canal involvement was seen; and in another 4 cases, a slight, isolated horizontal canal involvement was registered. Slight, isolated horizontal canal vestibular neuritis causing acute vestibular syndrome has not yet been reported in the literature. A three-step bedside oculomotor examination, the HINTS-test (head-impulse test, examination of gaze evoked nystagmus, and test of skew-deviation), suggested peripheral involvement in all cases with superior pattern VN and in cases when all three SCC were involved. It indicated 'stroke' in cases with inferior pattern and in the cases with isolated involvement of the horizontal canal. At follow-up, the horizontal canal function normalized in 55%, the anterior canal in 38%, and the inferior in 38%. When all cases were pooled, 14 patients recovered completely. In cases with severe initial decrease of gain in the horizontal canal (initial value less than 0.5), the canals had a 50 per cent chance to recover significantly.Conclusion: In vestibular neuritis, in cases with severe decrease of gain in the horizontal canal (initial value less than 0.5), the canal has a 50 per cent chance to recover significantly. The vertical canals have worse prognosis, and especially the inferior canals seldom improve. Slight, isolated horizontal canal vestibular neuritis may cause acute vestibular syndrome, most probably by the same mechanism as full-blown vestibular neuritis. In these cases, the three-step bedside oculomotor test may indicate cerebellar stroke (may be false positive). [ABSTRACT FROM AUTHOR]

• The variation tendency of horizontal or vertical nystagmus SPV is similar to the corresponding cupula response with the head's left-leaning angle changing. • Different head positions change the endolymphatic pressure gradient distribution. • The numerical model of bilateral SCCs could be used to explain the combined effects of each SCC's excitation or inhibition on human VOR under different head positions. The semicircular canals (SCCs) in the vestibular system can sense angular motion of the head, which performs a crucial role in maintaining the human's sense of balance. The different spatial orientations of the head affect the response of human SCCs to rotational movement. In this study, we combined the numerical model of bilateral human SCCs with vestibulo-ocular reflex experiments, and quantitatively investigated the responses of SCCs to constant angular acceleration when the head was in different left-leaning positions, including the head tilted 0°, 15°, 30°, 45°, 60°, 70°, 80°, and 90° to the left. The results showed that the vertical nystagmus slow-phase velocity (SPV) and the corresponding maximal cupula shear strain at the crista surface rose with an increase in the left-leaning angle of the head, reached a maximum at the position of the head tilted approximately 70° to the left, and then decreased gradually. Both the horizontal nystagmus SPV and the corresponding maximal cupula shear strain at the crista surface were the largest under the position of the head tilted 0° to the left, and decreased gradually as the left-leaning angle of the head increased. The numerical results of cupula shear strain at the crista surface in bilateral SCCs can quantitatively explain the combined effects of each SCC's excitation or inhibition on volunteers' nystagmus SPV under different head positions. In addition, a fluid-structure interaction investigation revealed that different left-leaning head positions changed the endolymphatic pressure gradient distribution in SCCs, which determined the transcupular pressure, cupula shear strain at the crista surface, and nystagmus SPV. [ABSTRACT FROM AUTHOR]