Normal modiolus: CT appearance in patients with a large vestibular aqueduct

PURPOSE: To determine the computed tomographic (CT) appearance of the normal modiolus and the pathologic alteration in patients with a large vestibular aqueduct and an otherwise normal-appearing cochlea. MATERIALS AND METHODS: Temporal bone CT studies obtained before and after a major upgrade of CT capability in 1992 were reviewed in four groups: Group A (1.5-mm section thickness) comprised 50 normal ears in 43 patients, group B (1-mm section thickness) comprised 75 normal ears in 50 patients, group C (1.5-mm section thickness) comprised 16 ears with a large vestibular aqueduct in 10 patients, and group D (1-mm section thickness) comprised 23 ears with a large vestibular aqueduct in 12 patients. All groups comprised adult and pediatric patients. RESULTS: In groups A and B, the normal modiolus was visualized in 90% and 100% of ears, respectively. In groups C and D, with a total of 39 ears with a large vestibular aqueduct and an otherwise normal cochlea, modiolar deficiency was demonstrated in 100% of ears. CONCLUSION: CT is an excellent technique for depicting the cochlear modiolus. Results suggest that all ears with a large vestibular aqueduct have associated cochlear modiolar deficiencies. Thus, a large vestibular aqueduct may be only occasionally, if ever, an isolated developmental anomaly of the inner ear.