PMC9621331_01
Axial scans of brain CT show (A) bilateral carotid siphon calcifications (white arrows) and (B-D) patent left PSC (yellow arrows). CT, computed tomography; L, left; PSC, posterior semicircular canal; R, right.
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F1
Only slight signs of bilateral carotid siphon calcifications were noted on a standard brain CT scan (Figure 1A), whereas serology for SARS-CoV-2 was negative. Despite low-resolution scans and thick slices, normal patency and morphology of the inner ear structures could be verified in temporal bone scans (Figures 1B-D).
Presenting scenario including (A) Pure-tone audiometry exhibiting bilateral high-frequency sensorineural hearing impairment, slightly greater on the right side. (B) Video-HIT was performed using a portable high-frame-rate video-oculography device (ICS Impulse, Natus Medical Inc, Denmark). Blue lines represent head impulses exciting left canals, orange lines correspond to impulses for right canals, green lines represent eye movements induced by the activation of VOR following each impulse, and red lines correspond to corrective saccades. The mean value of VOR-gain (eye velocity/head velocity) is reported for each canal. The hexagonal plot in the center of the figure summarizes the mean VOR gains for each canal; normal gains are shown in green, and deficient gains are in red. Gains are considered normal if> 0.8 for lateral canals and> 0.7 for vertical canals. A severe VOR-gain impairment for the left PSC (0.37) with mainly overt saccades can be observed, and a slight reduction of contralateral ASC VOR-gain (0.69). (C) C-VEMPs (above) and O-VEMPs (below) for air-conducted sounds recorded with a 2-channel evoked potential acquisition system (Viking, Nicolet EDX, CareFusion, Germany). Potentials were measured by delivering tone bursts (intensity: 100 dB nHL, frequency: 500 Hz, duration: 8 ms, stimulation rate 5 Hz) via headphones. The recording system used an EMG-based biofeedback monitoring method to minimize variations in muscle contractions and VEMPs amplitudes. Each stimulus was retested to assess the reproducibility of responses. For C-VEMPs, right and left lines correspond to myogenic responses (p1-n1) recorded on the right and left SCM muscle (i.e., right and left saccular responses), respectively. For O-VEMPs, being crossed responses, right and left lines representing potentials (n-p) are recorded under the left and right eye (i.e., right and left utricular responses), respectively. VEMP testing revealed normal responses on the right side (105.5 muV) and absent potentials on the left, whereas symmetrical amplitudes for ocular VEMPs (R: 4.4 muV and L: 5.7 muV) could be detected. AC, air-conduction; ASC, anterior semicircular canal; BC, bone-conduction; C, cervical; HIT, head impulse test; L, left; LA, left anterior; LL, left lateral; LP, left posterior; O, ocular; PSC, posterior semicircular canal; R, right; RA, right anterior; RL, right lateral; RP, right posterior; SCM, sternocleidomastoid; VEMPs, vestibular evoked myogenic potentials; VOR, vestibulo-ocular reflex.
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On micro-otoscopy, tympanic membranes were unremarkable, impedance audiometry was normal, while pure tone audiometry detected bilateral sensorineural high-frequency HL, with noise-induced components slightly greater in the right ear, comparable to the previous audiogram (Figure 2A). Video-HIT documented a severe impairment for the left PSC VOR-gain (0.37) with mainly overt saccades (Figure 2B), whereas bithermal caloric irrigations were within normality ranges. While O-VEMPs were symmetrical, C-VEMPs revealed no responses on the left side, consistent with saccular impairment (Figure 2C).
Instrumental picture observed at 3-months follow-up. (A) Video-HIT exhibited persistent selective loss for the left PSC VOR-gain (0.54) with only covert saccades. The affected canal VOR-gain is slightly increased compared to presenting values. (B) Cone-bream CT scans of the temporal bones with parasagittal reconstructed images along the Stenver plane detecting normally patent right-sided PSC (white arrow) and a near-complete PSC ossification on the left side (yellow arrows). CT, computed tomography; HIT, head impulse test; L, left; LA, left anterior; LL, left lateral; LP, left posterior; PSC, posterior semicircular canal; R, right; RA, right anterior; RL, right lateral; RP, right posterior; VOR, vestibulo-ocular reflex.
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F3
Skull vibration greatly enhanced spontaneous nystagmus and a new video-HIT confirmed the left PSC hypoactivity, despite a slight VOR-gain improvement (0.54) (Figure 3A). PSC ossification was found (Figure 3B), consistent with ischemic damage in the labyrinthine territory supplied by the PVA. Prophylactic treatment with acetylsalicylic acid was then suggested, and the patient was advised to undergo vestibular rehabilitation therapy.