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