Constructive interference in steady state-3DFT MR imaging of the inner ear and cerebellopontine angle.

PURPOSE To assess the value of a three-dimensional Fourier transformation MR technique "CISS" (constructive interference in steady state) in imaging the inner ear.

SUBJECTS We studied 50 normal inner ears (40 axial, 10 coronal) and 10 pathologic inner ears in 60 patients.

RESULTS The cochlea, semicircular canals, and vestibulum were visualized in detail. Cranial nerve VII and the cochlear, superior vestibular, and inferior vestibular branch of cranial nerve VIII were identified in 90%, 94%, 80%, and 88% of the cases, respectively. A vascular loop was recognized inside the internal auditory canal in 6%, and in the porus in 30%, of the cases. The high signal of the cerebrospinal fluid and labyrinthine fluids (perilymph and endolymph) on the CISS images made excellent delineation of tumors in the cerebellopontine angle and internal canal possible and allowed detection of tumoral labyrinth involvement. The thin sections, high resolution of the images, and capability of producing multiplanar and three-dimensional reconstructions often offered additional information.

CONCLUSIONS The CISS sequence allows detailed study of the normal and pathologic inner ear and promises to be highly valuable in the demonstration of the vascular loop.