Endolymphatic hydrops in the horizontal semicircular canal: A morphologic correlate for canal paresis in Ménière's disease

For almost 70 years, since Yamakawa and Hallpike and Cairns first discovered endolymphatic hydrops as the morphological hallmark of Menière’s disease, it has only been possible to visualize endolymphatic hydrops (ELH) on histologic staining of postmortem temporal bone specimens. In a landmark article, Nakashima et al. were the first to succeed in visualizing ELH in living Menière’s disease patients. This important new method is based on the preferential distribution of gadolinium-based contrast agents within perilymph (instead of endolymph), the intratympanic application of gadolinium-based contrast agent (yielding a higher concentration in perilymph than a standard dose applied intravenously), the high magnetic field strength of 3 Tesla, and specific magnetic resonance imaging sequences very sensitive to low concentrations of the contrast medium. In their original report, Nakashima et al. were able to demonstrate the presence of ELH in the cochlea and in the vestibulum. In a recent study, we were able to show a clear correlation between the degree of ELH in the cochlea and hearing loss, and also between the degree of ELH in the vestibulum and loss of saccular function. Interestingly, the degree of cochlear or vestibular hydrops did not correlate with loss of horizontal semicircular canal (hSCC) function as measured by caloric video-oculography. There was no positive correlation between loss of hSCC function and diameter of the hSCC ampulla in another recent report. These previous findings on structural-functional relationships in Menière’s disease are summarized in Table I. From histological postmortem studies, however, we know that ELH also occurs in the semicircular canals, albeit less often than in the cochlea and the sacculus. It has been previously reported that in some patients with severe vestibular hydrops, the perilymph spaces of the SCCs cannot be visualized by magnetic resonance imaging, and this has tentatively been attributed to the enlarged vestibular endolymphatic space blocking the perilymphatic communication of the oval and round window area with the SCC, thereby preventing the SCC from being reached by the contrast agent. However, an extension of the endolymphatic space inside the SCC has not been demonstrated before in a living patient. Due to their relatively small dimensions and complex geometry, the endolymph and perilymph spaces in the SCCs are not as easily differentially visualized as in the cochlea and the sacculus. In the present brief report, we present for the first time, to the best of our knowledge, in vivo morphological evidence of ELH in the horizontal semicircular canal in three out of four patients with definite unilateral Menière’s disease. The study protocol has been approved by the local university’s ethics committee.