Does CISS MRI Reliably Depict the Endolymphatic Duct in Children with and without Vestibular Aqueduct Enlargement?

Abstract

Background and purpose: High-resolution CT is the mainstay for diagnosing an enlarged vestibular aqueduct (EVA), but MR imaging may be an appealing alternative, given its lack of ionizing radiation exposure. The purpose of this study was to determine how reliably MR imaging demonstrates the endolymphatic duct and endolymphatic duct enlargement in hearing-impaired children.

Materials and methods: We performed a retrospective review of temporal bone high-resolution CT and MR imaging of hearing-impaired children evaluated between 2017 and 2020. Vestibular aqueduct diameter was measured on high-resolution CT. The vestibular aqueducts were categorized as being enlarged (EVA+) or nonenlarged (EVA-) using the Cincinnati criteria. The endolymphatic ducts were assessed on axial high-resolution CISS MR imaging. We categorized endolymphatic duct visibility into the following: type 1 (not visible), type 2 (faintly visible), and type 3 (easily visible). Mixed-effect logistic regression was used to identify associations between endolymphatic duct visibility and EVA. Interreader agreement for the endolymphatic duct among 3 independent readers was assessed using the Fleiss κ statistic.

Results: In 196 ears from 98 children, endolymphatic duct visibility on MR imaging was type 1 in 74.0%, type 2 in 14.8%, and type 3 in 11.2%; 20.4% of ears were EVA+ on high-resolution CT. There was a significant association between EVA+ status and endolymphatic duct visibility (P < .01). Endolymphatic duct visibility was type 1 in 87.1%, type 2 in 12.8%, and type 3 in 0% of EVA- ears and type 1 in 22.5%, type 2 in 22.5%, and type 3 in 55.0% of EVA+ ears. The predicted probability of a type 3 endolymphatic duct being EVA+ was 0.997. There was almost perfect agreement among the 3 readers for distinguishing type 3 from type 1 or 2 endolymphatic ducts.

Conclusions: CISS MR imaging substantially underdiagnoses EVA; however, when a type 3 endolymphatic duct is evident, there is a >99% likelihood of an EVA.

FIG 1.

Flow chart summarizing identification, selection, and exclusion of subjects from this study.

FIG 2.

Examples of the 3 types of ELD visibility observed on MR imaging. Upper row, Representative axial-view non-contrast-enhanced temporal bone CT images of 3 different ears from different patients. Lower row, Axial temporal bone CISS MR images corresponding to the same ears as the CT images directly above demonstrate type 1 (lower left image), type 2 (lower middle image), and type 3 ELDs (lower right image). Blue arrows in the upper row indicate the vestibular aqueducts; red arrows in the lower row indicate the visible ELDs.

FIG 3.

CISS MR images demonstrating additional examples of type 2 (faintly visible) ELDs (arrows) in 3 different patients: A, A 4-year-old girl with mild SNHL in the left ear. This patient demonstrated EVA on CT. B, A 1-year-old boy with profound SNHL in the right ear. This patient did not have VA enlargement on CT. C, An 8-year-old girl with profound SNHL in the left ear. This patient did not have VA enlargement on CT.

FIG 4.

CISS MR images demonstrating additional examples of type 3 (easily visible) ELDs (arrows) in 3 different patients. A, A 7-month-old girl with severe SNHL in the right ear. B, A 6-year-old boy with severe SNHL in the right ear. C, A 4-year-old girl with mild SNHL in the left ear. All patients in these images demonstrated EVA on CT.