Visualization and clinical relevance of the endolymphatic duct and sac in Ménière's disease

Abstract

Background: Ménière's disease (MD) is a chronic inner ear disorder with a multifactorial etiology. Decreased visualization of the endolymphatic duct (ED) and sac (ES) is thought to be associated with MD, although controversy exists about whether this finding is specific to MD. Recent literature has revealed that two distinct ES pathologies, developmental hypoplasia and epithelial degeneration, can be distinguished in MD using the angular trajectory of the vestibular aqueduct (ATVA) or ED-ES system as a radiographic surrogate marker. It has been suggested that these two subtypes are associated with distinct phenotypical features. However, the clinical differences between the ATVA subtypes require further validation.

Research objective: The objective of this study is to investigate whether (1) non-visualization of the ED-ES system is a discriminative radiological feature for MD in a cohort of vertigo-associated pathologies (VAPs) and whether (2) different angular trajectories of the ED-ES system in MD are associated with distinguishable clinical features.

Setting: The study was conducted in the Vertigo Referral Center (Haga Teaching Hospital, The Hague, the Netherlands).

Methods: We retrospectively assessed 301 patients (187 definite MD and 114 other VAPs) that underwent 4h-delayed 3D FLAIR MRI. We evaluated (1) the visibility of the ED-ES system between MD and other VAP patients and (2) measured the angular trajectory of the ED-ES system. MD patients were stratified based on the angular measurements into α_exit ≤ 120° (MD-120), α_exit 120°-140° (MD-intermediate), or α_exit ≥ 140° (MD-140). Correlations between ATVA subgroups and clinical parameters were evaluated.

Results: Non-visualization of the ED-ES system was more common in definite MD patients compared with other VAPs (P < 0.001). Among definite MD patients, the MD-140 subtype demonstrated a longer history of vertigo (P = 0.006), a higher prevalence of bilateral clinical disease (P = 0.005), and a trend toward a male preponderance (p = 0.053). No significant differences were found between ATVA subgroups regarding the presence or severity of auditory symptoms, or the frequency of vertigo attacks.

Conclusion: Non-visualization of the ED-ES system is significantly associated with MD. Among MD patients with a visible ED-ES system, we demonstrated that the MD-140 subtype is associated with a longer disease duration, a higher prevalence of bilateral MD, and a trend toward a male preponderance.

Keywords: MRI; Ménière; clinical features; endolymphatic duct; endolymphatic sac.

Figure 1

Inclusion flowchart. ATVA, angular trajectory of the vestibular aqueduct; ED, endolymphatic duct; ES, endolymphatic sac; Gd, gadolinium; HED, hydropic ear disease; MD, Ménière's disease; MRI, magnetic resonance imaging; VAP, vertigo-associated pathology.

Figure 2

Morphology of the ED-ES complex on axial contrast-enhanced FLAIR images. The visibility of the ED-ES system was evaluated from the posteromedial aspect of the vestibule to the opercular region. (A) Normal visualization of the ED-ES system (long arrow) in a patient diagnosed with vestibular migraine. (B) Non-visualization of the ED-ES system in patient with definite MD. (C, D) Corresponding schematic depiction of the MR images. The visible parts of the cochlea, vestibule, and semicircular canals are depicted in orange. In (C), the saccule and utricle are depicted in blue and green, respectively. Note the presence of vestibular hydrops (depicted in blue) in (D).

Figure 3

Angular trajectory of the ED-ES system in definite MD cases with MD-120 (A, B), MD-intermediate (C, D), and MD-140 (E, F) morphologies. (A, C, E) axial 4 h-delayed Gd-enhanced 3D FLAIR MRI, the long arrows indicate the ED-ES system in the opercular region. The ED-ES system lies in close proximity to the posterior semicircular canal (long arrow head). (B, D, F) show the corresponding ATVA by fitting a predefined shape (magenta shape) into the bony boundaries of the vestibule and horizontal semicircular canal. The red line (I₁) is attached to this shape at a fixed angle of 14°, representing the entrance angle (α_entrance) of the proximal ED in the temporal bone at its origin from the vestibule. The green line (I₂) was fitted parallel to the trajectory along which the ES exits the temporal bone. The exit angle (α_exit) of the ED-ES system was calculated by the software as the angle between I₁ and I₂. Note the presence of vestibular hydrops in all cases (dashed arrow in A, C, E), cochlear hydrops in the MD-intermediate and MD-140 cases (short arrowhead in C, E), as well as increased perilymphatic enhancement in the MD-intermediate case (thick arrow in C).