OVERLAPPING THIN-SECTION FAST SPIN-ECHO MR OF THE LARGE VESTIBULAR AQUEDUCT SYNDROME

PURPOSE: To evaluate a high-resolution, thin-section fast spin-echo MR imaging technique of the inner ear to identify the large vestibular a queduct syndrome seen on temporal bone CT scans. METHODS: We retrospec tively reviewed the temporal bone CT scans of 21 patients with hearing loss and enlarged bony vestibular aqueducts by CT criteria. High-reso lution fast spin-echo MR imaging was then performed on these patients using dual 3-inch phased-array receiver coils fixed in a temporomandib ular joint holder and centered over the temporal bones. MR imaging inc luded axial and oblique sagittal fast spin-echo sequences. The diamete r of the midvestibular aqueduct on CT scans and the signal at the leve l of the midaqueduct on MR images were measured on axial sequences, th en compared. High-resolution MR imaging with the same protocol was per formed in 44 control subjects with normal ears, and similar measuremen ts were taken, RESULTS: The average size of the enlarged bony vestibul ar aqueduct on CT scans was 3.7 mm, and the average width of the signa l from within the enlarged aqueduct on MR images was 3.8 mm. Statistic al analysis showed excellent correlation. MR images alone displayed th e enlarged extraosseous endolymphatic sac, which accompanies the enlar ged aqueduct in this syndrome. Five ears in three patients with enlarg ed bony vestibular aqueducts on CT scans showed no evidence of an enla rged endolymphatic duct or sac on MR images. An enlarged endolymphatic sac was seen on MR images in one patient with a bony Vestibular aqued uct, which had normal measurements on CT scans. MR imaging alone ident ified a single case of mild cochlear dysplasia (Mondini malformation). In the 88 normal ears studied, the average size of the endolymphatic sac at its midpoint between the common crus and the external aperture measured on MR images was 0.8 mm (range, 0.5 to 1.4 mm). In 25% of the normal ears, no signal was seen from within the Vestibular aqueduct, CONCLUSION: Thin-section, high-resolution fast spin-echo MR imaging of the inner ear is complementary to CT in studying patients with the la rge vestibular aqueduct syndrome, as MR imaging better displays the so ft tissues and fluid of the membranous labyrinth.