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To evaluate pre- and post-operative semicircular canal function in patients with vestibular schwannoma (VS) by the video Head Impulse Test (vHIT). Nineteen patients with VS who underwent surgery were enrolled in this study. The gain in vestibulo-ocular reflex (VOR) and the degree of scatter in catch-up saccades were examined pre- and post-operatively for the semicircular canals in VS patients. Ten of 19 cases (52.6 %) with VS were defined as demonstrating both superior vestibular nerve (SVN) and inferior vestibular nerve (IVN) impairment from the results of pre-operative vHIT. Hearing level and subjective vestibular symptoms showed significant correlations with pre-operative semicircular canal function. Compared to pre-operative vHIT results, VOR gains within 1 month after surgery were significantly reduced in all three canals; however, significant differences had disappeared in the anterior and posterior semicircular canals at 6 months after surgery. Cases of unknown origin had a significantly greater reduction in posterior semicircular canal function after surgery compared with those with disease of IVN origin. As vHIT could evaluate pre-operative vestibular nerve impairment, post-operative VOR gain reduction and the degree of vestibular compensation, semicircular canal function evaluated by vHIT provides a good deal of useful information regarding VS patients undergoing surgery compared to caloric testing, and vHIT should be performed pre- and post-operatively for patients with VS. [ABSTRACT FROM AUTHOR]

• 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. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Diffusion-weighted (DW) imaging detects cellular changes. Loss of tumor cells post radiosurgery results in alteration in the Cellular density and thus changes in apparent diffusion coefficients (ADCs). Low ADC values represent a higher tumor cellularity, a higher tumor-grade and may even be a marker for a higher tumor activity. Purpose of the study is to investigate the clinical usefulness of ADC values for evaluating VSs and to assess the correlation of DW imaging measurements with radiosurgical effects on the tumors.Materials/methods: The authors conducted a retrospective evaluation involving 36 patients harboring solid (28 pts.) or cystic vestibular schwannomas (8 pts.) who underwent single fraction Linac based SRS. The patients underwent serial MR imaging, including DW imaging, before SRS and at 6mo. intervals thereupon following the procedure. The ADCs were calculated from echo-planar DW images, and mean ADC values were compared at each follow-up. To minimize the effect of diffusion anisotropy, an average of the values obtained for the 3 diffusion directions was calculated to provide the trace of the diffusion tensor. Data were analyzed using a t-test to compare the mean ADC values obtained before & after SRS.Results: The mean follow-up period in this study was 32.5 months (range 16 -56 months). Imaging studies demonstrated a reduction in tumor volume in 22 patients (61.3%) and tumor growth arrest in 11 patients (33%). There was tumor enlargement at 18, 36, and 42 months in the remaining 3 patients (8.3%). The mean ADC value before SRS for all solid VSs was 1.2 ± 0.17 × 10-3 mm2/second, which significantly increased 6 months after SRS and continued to increase with time (P = 0.0076). The mean ADC value for treated solid tumors as of the last mean follow-up of 36 months (range 18-60 months) was 1.92 ± 0.26 × 10-3 mm2/second (range 1.60-2.7 × 10-3 mm2/second), which was significantly higher than that before SRS (P = 0.0001). Tumor volumes were positively related to ADC values (P = 0.03). The mean ADC value before SRS for all cystic VSs was 2.09 ± 0.24 × 10-3 mm2/second (range 1.80-2.58 × 10-3 mm2/second). The mean ADC value for treated cystic tumors as of the last mean follow-up of 38 months (range 18-48 months) was 1.9 ± 0.42 × 10-3 mm2/second. In 3 patients harboring solid VSs, the tumor enlarged after SRS but the ADC values were higher than those before SRS.Conclusion: ADC changes precede the real change in tumor size detected on routine follow-up MR images. ADC values of solid tumors significantly increased, even before a change in tumor volume was evident and should be incorporated in VS routine MR imaging post SRS.Author Disclosure: V. Shankar: None. V. Sai Shreya: None. R. Kumar: None. C. Haritha: None. A.K. Karthikayan: None. R. Adhityan: None. P. Bhavya: None. H. Vyas: None. A. Bhange: None. [ABSTRACT FROM AUTHOR]