Caloric Test, and Qualitative and Quantitative vHIT Analysis in Vestibular Schwannoma

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OBJECTIVES: To investigate relationships and discordant results between caloric testing and video head impulse testing (vHIT) among patients with unilateral vestibular schwannoma (VS), trying to establish if caloric testing and vHIT may provide complementary information on vestibular assessment. STUDY DESIGN: Retrospective case review. SETTING: Tertiary care academic center. PATIENTS: 218 patients affected by unilateral VS and managed by "wait and scan" (WS), microsurgery (MS), or fractionated stereotactic radiotherapy (SRT). The analysis included patients' age, tumor size (KOOS stage), hearing level, facial nerve function, vestibular function, tumor control, and complications.The subjects' vestibular function was assessed evaluating the caloric response, vHIT gains for lateral canals and saccades, with and without gain abnormalities. RESULTS: In the 167 eligible patients, the most common finding was both caloric and vHIT abnormal results (74 patients). In 40 cases, caloric test abnormal response was not associated with ipsilesional vestibular oculomotor reflex (VOR) amplitude alterations. In 53 patients, caloric tests and vHIT showed no abnormalities. In the three groups of patients, the number of compensatory saccadic eye movements after head motion was significantly higher, which were strongly correlated with caloric unilateral weakness (UW). Tumor size was significantly associated with an increase both in caloric UW and VOR asymmetry. CONCLUSION: Results highlight the importance of an accurate vHIT morphological analysis in the context of patients affected by VS. Indeed, given the relationship between vestibular deficit and number of compensatory saccades, our data further suggest that an increase in the generation of late compensatory saccadic events may reveal a vestibular deficit not adequately characterized by VOR gain analysis. A correct vestibular assessment must include the caloric test and the vHIT including both qualitative and quantitative analysis of the saccades in the presence of a normal VOR gain and normal symmetry.

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