Magnetic resonance imaging features of large endolymphatic sac compartments: audiological and clinical correlates

Abstract

Objectives: (1) To study the prevalence and characteristics of large endolymphatic sac internal compartments on thin-section T2-and T2*-weighted magnetic resonance imaging, and to relate these to other large endolymphatic sac magnetic resonance imaging features, and (2) to correlate the compartment imaging features, endolymphatic sac size and labyrinthine anomalies with the patients' clinical and audiological data.Method: Magnetic resonance imaging studies for 38 patients with large endolymphatic sac anomalies were retrospectively reviewed in a tertiary referral centre. Endolymphatic sac compartment presence, morphology and imaging signal were assessed. Endolymphatic sac size and labyrinthine anomalies were also recorded. Endolymphatic sac compartments and other imaging features were correlated with clinical and audiological data.Results: Compartments were present in 57 per cent of the imaged endolymphatic sacs, but their presence alone did not correlate with other imaging features or clinical data. The endolymphatic sac : internal auditory meatus signal ratio was associated with a history of sudden or fluctuating hearing loss. Hearing loss correlated with opercular and extraosseous endolymphatic sac size measurements. A larger midpoint intraosseous endolymphatic sac size was associated with clear fluid loss at cochlear implantation.Conclusion: The magnetic resonance imaging characteristics of large endolymphatic sac compartments have been defined. The endolymphatic sac size and distal compartment signal should be recorded, as these provide prognostic information and assist the planning of appropriate interventions.Key words: Hearing Loss; Endolymphatic Sac; Anatomy; Magnetic Resonance IntroductionThe large endolymphatic sac anomaly is a congenital abnormality which results in acquired hearing loss. It is one of the most frequent malformations of the inner ear recognisable on imaging studies.

Detailed MR imaging assessment of endolymphatic hydrops in patients with SLC26A4 mutations.

“…Previous MR imaging studies have demonstrated that the enlarged ES contains different signal intensities on T1-or T2-weighted images compared with cerebrospinal fluid and other labyrinthine fluid. It has been considered that this is a consequence of the high protein concentration within the ES [32][33][34] . In human and animal protein concentration studies of the ES, the protein concentration of luminal fluid in the ES was shown to be markedly higher than that of the cochleo-vestibular endolymph and perilymph, even in LVA ears with SLC26A4 mutations, and creates a high osmotic gradient [35][36][37][38] .Thus, one possible explanation is that such high osmotic pressure and protein content may facilitate the penetration of the contrast agent into the endolymphatic sac, resulting in the high intensity signals for the ES and ED, particularly when the IV injection method is used.…”

“…The luminal area of the ES is known to contain a homogeneous substance that is believed to consist of macromolecular complexes composed of glycosaminoglycans, sulphated proteoglycans and glycoproteins [40 , 41] . Connor et al postulated that the low signal intensity compartment on T2-weighted MR images may correspond to these homogenous substances in the ES [34] . Therefore, the lower enhanced area on the MR images obtained using IV may imply the existence of a high protein compartment in the lumen of the ED and ES.…”