Inner ear malformations (IEM) represent a diagnostic challenge. A correct diagnosis
can be decisive for therapy and thus of high clinical relevance. The diagnostic standard
includes high-resolution computed tomography (hrCT). Different classification systems
for IEM diagnosis on hrCT have been established in the past. The aim of this study
was to evaluate the utility and reliability of 3D reconstruction and volumetry of
inner ear structures in the diagnosis of IEM. In total, 99 temporal bones were examined
(cochlear hypoplasia [CH]: n=18, incomplete partition [IP] type I: n=6 and type III:
n=6, Mondini malformation: n=11, enlarged vestibular aqueduct syndrome: n=15, control:
n=43). Diagnosis was performed by experienced neuroradiologists. Semiautomated segmentation
was used to obtain the volume of particular inner ear structures. Using axial hrCT,
common 2D measurements were aditionally performed. 2D and 3D measurements were evaluated
in terms of correlation and interinvestigator reliability. IEM showed significant
differences in cochlear and vestibular volumes depending on malformation type compared
with the control group. Compared to the control group (mean 78.0 mm3), only CH showed
a significantly smaller volume of the cochlea (mean 30.2 mm3; p<0.0001). The 3D measurements
showed a good interrater-reliability. The obtained volumes showed good correlations
with previously existing 2D measurement parameters. To classify the vestibular organ
as hypoplastic, we propose a cut-off value of less than 80mm3, as dilated one of greater
than 135mm3. A cut-off value of less than 60mm3 may indicate a hypoplastic cochlea.
Reference values for volumes of inner ear structures may be helpful in diagnosing
IEM.
