PMC5765242_01
A: The vestibulo-ocular reflex (VOR) gain values are decreased for left horizontal (HC, 0.1, normal range >=0.8) and both posterior canals (PCs, 0.3 for the right PC, and 0.1 for the left PC, normal range >=0.7), but normal for right horizontal and both anterior canals (ACs, 1.0 for the right HC, 0.9 for the right AC, and 0.8 for the left AC, normal range >=0.7). Overt saccades are found for these canals with decreased VOR gains, while covert saccades are observed during stimulation of the right PC and left AC. B: Caloric tests show bilaterally reduced responses with the summated slow phase velocities (SPVs) of the induced nystagmus at 14 /s (8 /s in the right ear, 6 /s in the left ear). C: Video head impulse tests one week later document reduced VOR gains and overt catch-cup saccades for all six semicircular canals (0.2 for the right HC, 0.1 for the left HC, 0.6 for the right AC, 0.4 for the left AC, 0.1 for the right PC, 0.0 for the left PC). D: Brain MRIs reveals nodular gadolinium enhancements within both internal auditory canals (arrows) in addition to increased signals in the cerebellar vermis (arrowheads). ACs: anterior canals, HC: horizontal canal, PCs: posterior canals, SPV: slow phase velocity, VOR: vestibulo-ocular reflex.
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HITs also revealed a decreased VOR gain and corrective saccades for left horizontal and both posterior canals (Fig. 1A). However, caloric irrigation elicited bilaterally reduced responses (Fig. 1B). He additionally developed leftside facial palsy 2 weeks later. Follow-up video HITs also revealed decreased gains and corrective saccades for all six semicircular canals (Fig. 1C). Brain MRIs with gadolinium enhancement disclosed nodular enhancements within both internal auditory canals (IACs) along with an increased signal of the cerebellar vermis (Fig. 1D).