The human vestibulo-ocular reflex and compensatory saccades in schwannoma patients before and after vestibular nerve section

• Published in: Clinical neurophysiology 2022-06, Vol.138, p.197-213
• Main Authors: Pogson, Jacob M., Taylor, Rachael L., Bradshaw, Andrew P., McGarvie, Leigh, D'Souza, Mario, Flanagan, Sean, Kong, Jonathan, Biggs, Nigel, Shivalingam, Brindha, Greenberg, Simon, Croxson, Glen, Halmagyi, G. Michael, Welgampola, Miriam S.
• Format: Article
• Language: English
• Subjects: Saccades; Schwannoma; Vestibular system; Vestibulo-ocular reflex; Video head impulse test
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2022.02.014

•In unoperated vestibular schwannoma, ipsilesional canals show decreased vestibulo-ocular reflex (VOR) gain and increased saccade amplitude and frequency.•One week after unilateral vestibular deafferentation lesioned canal gains drop by 0.22–0.35 and first saccade frequency and amplitudes increase by 37% and 2.9°.•The video head-impulse test excitation/dis-facilitation VOR asymmetry is less for the intact posterior canal than for the other canals. To examine the vestibulo-ocular reflex (VOR) and compensatory-saccades before and after complete unilateral vestibular deafferentation (UVD). Forty patients were studied before and after surgery for vestibular or facial schwannoma using the video head-impulse test (vHIT) and multivariable regression. Prior to UVD (median(IQR), 14(58.4) days), the average VOR-gain towards the lesioned-ear was lower than in normal for all semicircular canals (lateral, anterior, posterior: 0.69, 0.72, 0.49). One-week after UVD (5(3.0) days) VOR gains were further reduced (0.22, 0.37, 0.27), however, within one-year after UVD (171(125.0) days) the lesioned-ear VOR gains had slightly increased (+0.08, +0.11, +0.03), maximally for the anterior-canal. After UVD, the VOR gain asymmetry (gain towards minus away from intact-ear) was lower for the intact posterior-canal plane (0.56, 0.56, 0.22). For the lesioned canals, the frequency and amplitude of the first compensatory-saccade increased from 61–93% and 1.9–3.6° pre-surgery, to 98–99% and to 3.1–5.9° one-week post-surgery and remained unchanged over one-year; second saccade frequency and amplitude decreased over the same timespan. After UVD the high-acceleration VOR for the intact posterior-canal plane is more symmetrical than the other canals. First compensatory-saccades adapt within one week and subsequently change only marginally. Saccade compensation from surgical UVD is near complete by one-week.