Subtle Malformation of the Cochlear Apex and Genetic Abnormalities: Beyond the "Thorny" Cochlea

Abstract

With the routine use of high-resolution heavily T2-weighted sequences to evaluate patients with hearing deficits, new, subtle phenotypes of cochlear malformations are being discovered and an increasing number of genotype-phenotype correlations are being found through a reverse phenotype approach, which can help guide geneticists. In this brief report, we present subtle malformations of the apical turn of the cochlea related to 3 genetic mutations, emphasizing the importance of a careful assessment of the cochlear apex.

FIG 1.

A, High-resolution 3D heavily T2-weighted MR images of the inner ear and IAC in a patient with a TKFC-related disorder. There is an extra turn (arrows) at the apical portion of the cochlea beyond the usual apical turn and an overall greater cochlear height. The cochlear nerves are present, the modiolus is normal in appearance, and there is normal internal partitioning. Contrast this appearance with that of the normal cochlear apical turn seen in Fig 3B, without an extra turn beyond it. B, Coronal CT image through the cochlea shows the method to measure cochlear height as defined by Shim et al: The maximal height of the cochlea is measured along an axis perpendicular to the oval window (white line).

FIG 2.

High-resolution 3D heavily T2-weighted MR images of the inner ear and IAC in a patient with a ZNF699 gene mutation. The uppermost turn of the cochlear apex following the middle turn has a short and stumpy shape (arrows).

FIG 3.

High-resolution 3D heavily T2-weighted MR image of a typical SIX1-BOR protuberant “thorny” tip of the cochlea (arrow in A) in comparison with a healthy control in whom the apical turn is uniform and relatively flat and tubular (arrow in B).