Case Report: Filling Defect in Posterior Semicircular Canal on MRI With Balanced Steady-State Gradient-Echo Sequences After Labyrinthine Ischemia in the Common Cochlear Artery Territory as an Early Sign of Fibrosis

Abstract

We describe a rare case of posterior semicircular canal (PSC) fibrosis following acute labyrinthine ischemia in the territory supplied by the common cochlear artery (CCA) and review the relevant literature. A 71-year-old man with multiple vascular risk factors presented 12 days after the onset of acute vertigo and profound left-sided hearing loss. Right-beating spontaneous nystagmus with downbeat components elicited by mastoid vibrations and headshaking was detected. The video head impulse test (vHIT) revealed an isolated hypofunction of the left PSC, whereas vestibular evoked myogenic potentials (VEMPs) showed ipsilateral saccular loss. The clinical presentation and instrumental picture were consistent with acute ischemia in the territory supplied by left CCA. Compared to previous imaging, a new MRI of the brain with 3D-FIESTA sequences highlighted a filling defect in the left PSC, consistent with fibrosis. Hearing function exhibited mild improvement after steroid therapy and hyperbaric oxygen sessions, whereas vHIT abnormalities persisted over time. To the best of our knowledge, this is the only case in the literature reporting a filling defect on MRI, consistent with semicircular canal fibrosis following acute labyrinthine ischemia. Moreover, PSC fibrosis was related with poor functional outcome. We therefore suggest using balanced steady-state gradient-echo sequences a few weeks following an acute lesion of inner ear sensors to detect signal loss within membranous labyrinth consistent with post-ischemic fibrosis. Besides addressing the underlying etiology, signal loss might also offer clues on the functional behavior of the involved sensor over time. In cases of acute loss of inner ear function, a careful bedside examination supplemented by instrumental assessments, including vHIT and VEMPs, of vestibular receptors and afferents may be completed by MRI with balanced steady-state gradient-echo sequences at a later time to confirm the diagnosis and address both etiology and functional outcome.

Keywords: common cochlear artery; inner ear MRI; labyrinthine fibrosis; labyrinthine ischemia; posterior semicircular canal; vestibular-evoked myogenic potentials; video-head impulse test.

Figure 1

(A–C) Brain MRI performed 4 years prior to left-sided labyrinthine ischemia exhibiting (A) Slight signs of periventricular leukoaraiosis on axial T2-weighted FLAIR (fluid-attenuated inversion recovery) images. (B) Axial and (C) sagittal MRI with 3D-FIESTA (fast imaging employing steady-state acquisition) sequences showing normally fluid filled semicircular canals on both sides (red arrows indicate left posterior semicircular canal). (D–F) Brain MRI performed 14 days after left-sided labyrinthine ischemia showing (D) Increased areas of periventricular leukoaraiosis and widened cerebrospinal fluid spaces on atrophic basis on axial T2-weighted FLAIR images. (E) Axial and (F) sagittal MRI with 3D-FIESTA sequences showing filling defect within the left posterior semicircular canal (black arrows). A, anterior; L, left; P, posterior; R, right.

Figure 2

(A,B) Presenting scenario including (A) Pure-tone audiometry exhibiting right-sided high-frequency sensorineural hearing impairment and profound left-sided hearing loss. (B) vHIT. 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. Mean value of VOR-gain (eye velocity/head velocity) is reported for each canal. The hexagonal plot in the center of the figure summarizes mean VOR-gains for each canal; normal gains are shown in green and deficient gains are in red. A selective deficient VOR-gain for the left posterior semicircular canal (0.59) with overt saccades can be observed. Cervical VEMPs (C) and ocular VEMPs (D) for air-conducted sounds. For cervical 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 ocular VEMPs, being crossed responses, right and left lines represent potentials (n–p) recorded under the left and right eye (i.e., right and left utricular responses), respectively. VEMPs testing revealed normal responses on the right side (83 μV at 100 dB HL stimuli) and absent potentials on the left, whereas symmetrical amplitudes for ocular VEMPs (R: 6 μV and L: 5 μV at 100 dB HL stimuli) could be detected. L, left; LA, left anterior; LL, left lateral; LP, left posterior; R, right; RA, right anterior; RL, right lateral; RP, right posterior; SCM, sternocleidomastoid; vHIT, video head impulse test; VEMPs, vestibular evoked myogenic potentials; VOR, vestibulo-ocular reflex.

Figure 3

(A–C) Instrumental picture following steroids and hyperbaric oxygen therapy. (A) Pure-tone audiometry exhibiting partial recovery for right-side hearing function with a pure-tone average (500 Hz−4 kHz) of 77.5 dB. (B) Standard speech audiometry in silent setting showing optimal (100%) and poor (20%) speech discrimination score on the right and left sides, respectively. (C) vHIT showing persistent selective loss for left posterior canal VOR-gain (0.46) with both overt and covert saccades. Affected canal VOR-gain is further impaired compared to presenting values. (D,E) Temporal bones HRCT scans with axial (D) and parasagittal reconstructed image along the Stenver plane (E) excluding signs of posterior semicircular canal ossification on the left side (yellow arrows). HRCT, high-resolution computed tomography; L, left; LA, left anterior; LL, left lateral; LP, left posterior; R, right; RA, right anterior; RL, right lateral; RP, right posterior; vHIT, video head impulse test; VOR, vestibulo-ocular reflex.

Figure 4

Inner ear vascular supply. Labyrinthine receptors mainly supplied by the anterior vestibular artery and the common cochlear artery are in yellow and in light blue, respectively. AICA, anterior-inferior cerebellar artery; HSC, horizontal semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal.