The "hype" of hydrops in classifying vestibular disorders: a narrative review

Abstract

Background: Classifying and diagnosing peripheral vestibular disorders based on their symptoms is challenging due to possible symptom overlap or atypical clinical presentation. To improve the diagnostic trajectory, gadolinium-based contrast-enhanced magnetic resonance imaging of the inner ear is nowadays frequently used for the in vivo confirmation of endolymphatic hydrops in humans. However, hydrops is visualized in both healthy subjects and patients with vestibular disorders, which might make the clinical value of hydrops detection on MRI questionable.

Objective: To investigate the diagnostic value of clinical and radiological features, including the in vivo visualization of endolymphatic hydrops, for the classification and diagnosis of vestibular disorders.

Methods: A literature search was performed in February and March 2019 to estimate the prevalence of various features in healthy subjects and in common vestibular disorders to make a graphical comparison between healthy and abnormal.

Results: Of the features studied, hydrops was found to be a highly prevalent feature in Menière's disease (99.4%). Though, hydrops has also a relatively high prevalence in patients with vestibular schwannoma (48.2%) and in healthy temporal bones (12.5%) as well. In patients diagnosed with (definite or probable) Menière's disease, hydrops is less frequently diagnosed by magnetic resonance imaging compared to the histological confirmation (82.3% versus 99.4%). The mean prevalence of radiologically diagnosed hydrops was 31% in healthy subjects, 28.1% in patients with vestibular migraine, and 25.9% in patients with vestibular schwannoma. An interesting finding was an absolute difference in hydrops prevalence between the two diagnostic techniques (histology and radiology) of 25.2% in patients with Menière's disease and 29% in patients with vestibular schwannoma.

Conclusions: Although the visualization of hydrops has a high diagnostic value in patients with definite Menière's disease, it is important to appreciate the relatively high prevalence of hydrops in healthy populations and other vestibular disorders. Endolymphatic hydrops is not a pathognomic phenomenon, and detecting hydrops should not directly indicate a diagnosis of Menière's disease. Both symptom-driven and hydrops-based classification systems have disadvantages. Therefore, it might be worth to explore features "beyond" hydrops. New analysis techniques, such as Radiomics, might play an essential role in (re)classifying vestibular disorders in the future.

Keywords: Disease; Distinctiveness; Endolymphatic hydrops; Magnetic resonance imaging; Menière’s; Symptoms; Vestibular disorders.

Fig. 1

Graphical representation of feature distinctiveness in a four-dimensional (x,y,r,α) bubble chart. Estimated prevalences in patients diagnosed with MD and in healthy references were plotted on the x-axis and y-axis, respectively. This resulted in a low, moderate, or high level of distinctiveness. The overall feature prevalence in both health and disease were presented as bubble size (r). The reliability of the results were presented by transparency (α). Features plotted under the reference line were distinctive for MD. The absolute distance between EH (histology) and EH (radiology) represented the discrepancy in distinctiveness between the two techniques

Fig. 2

Graphical representation of feature distinctiveness in a four-dimensional (x,y,r,α) bubble chart. Estimated prevalences in patients diagnosed with vestibular schwannoma and healthy references were plotted on the x-axis and y-axis, respectively. This resulted in a low, moderate, or high level of distinctiveness. The overall feature prevalence in both health and disease were presented as bubble size (r). The reliability of the results was presented by transparency (α). Features plotted under the reference line were distinctive for vestibular schwannoma. The absolute distance between EH (histology) and EH (radiology) represented the discrepancy in distinctiveness between the two techniques

Fig. 3

Graphical representation of feature distinctiveness in a four-dimensional (x, y, r, α) bubble chart. Estimated prevalences in patients diagnosed with vestibular migraine and healthy references were plotted on the x-axis and y-axis, respectively. This resulted in a low, moderate, or high level of distinctiveness. The overall feature prevalence in both health and disease were presented as bubble size (r). The reliability of the results were presented by transparency (α). Features plotted under the reference line were distinctive for vestibular migraine