Is CT or MRI the optimal imaging investigation for the diagnosis of large vestibular aqueduct syndrome and large endolymphatic sac anomaly?

Abstract

Background and purpose: We explored whether there was a difference between measurements obtained with CT and MRI for the diagnosis of large vestibular aqueduct syndrome or large endolymphatic sac anomaly, and whether this influenced diagnosis on the basis of previously published threshold values (Valvassori and Cincinnati). We also investigated whether isolated dilated extra-osseous endolymphatic sac occurred on MRI. Secondary objectives were to compare inter-observer reproducibility for the measurements, and to investigate any mismatch between the diagnoses using the different criteria.

Materials/methods: Subjects diagnosed with large vestibular aqueduct syndrome or large endolymphatic sac anomalies were retrospectively analysed. For subjects with both CT and MRI available (n = 58), two independent observers measured the midpoint and operculum widths. For subjects with MRI (± CT) available (n = 84), extra-osseous sac widths were also measured. Results There was no significant difference between the width measurements obtained with CT versus MRI. CT alone diagnosed large vestibular aqueduct syndrome or large endolymphatic sac anomalies in 2/58 (Valvassori) and 4/58 (Cincinnati), whilst MRI alone diagnosed them in 2/58 (Valvassori). There was 93% CT/MRI diagnostic agreement using both criteria. Only 1/84 demonstrated isolated extra-osseous endolymphatic sac dilatation. The MRI-based LVAS/LESA diagnosis was less dependent on which criteria were used. Midpoint measurements are more reproducible between observers and between CT/MR imaging modalities.

Conclusion: Supplementing MRI with CT results in additional diagnoses using either criterion, however, there is no net increased diagnostic sensitivity for CT versus MRI when applying the Valvassori criteria. Isolated enlargement of the extra-osseous endolymphatic sac is rare.

Keywords: Computed tomography; Deafness; Inner ear; Large endolymphatic sac anomaly; Large vestibular aqueduct syndrome; Magnetic resonance imaging.

Fig. 1

Intra-osseous measurement methodology. T2 DRIVE axial MR images demonstrating the vestibular, opercular and midpoint planes in a patient with bilateral large endolymphatic sac anomaly but no septations. a White line corresponds to the vestibular plane defined by the horizontal plane at the level of the dorsal common crus as it arises from the vestibule. b White line corresponds to the opercular plane defined by the horizontal plane at the level of the superior opercular lip. Black line corresponds to the opercular measurement. c White line corresponds to the midpoint plane, defined as halfway anteroposteriorly between the vestibular and opercular planes. Black line corresponds to the mid-point measurement

Fig. 2

CT positive for LVAS but MRI negative for LESA. Axial CT (a) and T2 CISS axial MR image (b) demonstrates a case in which there was 2 mm measurement at the operculum on CT, thus Cincinnati criteria positive for LVAS (black open arrow) but not on MRI (white filled arrow)

Fig. 3

Intra-osseous measurements diagnose LESA on MRI but extra-osseous sac not enlarged. T2 DRIVE axial images show widened midpoint measurements bilaterally (white open arrows in a). There is an enlarged extra-osseous sac on the left (white open arrow in b) but not on the right (white filled arrow in b)

Fig. 4

Isolated enlargement of the extra-osseous sac. T2 CISS axial image (a) demonstrates a very short splayed LESA without a clearly defined operculum and no widened intra-osseous measure is defined on axial images (white open arrow). An operculum is just defined on the left (white filled arrow). The sagittal oblique reformat b demonstrates a minimally prominent pre isthmic segment (white open arrow) but that the remaining LESA corresponds to an enlarged extra-osseous sac (white filled arrow)

Fig. 5

Cincinnati criteria positive but Valvassori criteria negative cases. T2 CISS axial images (a) and (b) demonstrate an elongated intra-osseous endolymphatic sac/duct. The midpoint (white open arrow in a) is not widened on either criteria. At the opercular portion, there is widening (white open arrow in b) so the case is Cincinnati criteria positive but Valvassori criteria negative. Note how it is difficult to define the transition between the bony operculum and the low signal dura overlying the extra-osseous sac. c A different patient demonstrated a minimally widened (1.2 mm) midpoint on CT so the case is also Cincinnati criteria positive but Valvassori criteria negative