Pathology of the membranous labyrinth: comparison of T1- and T2-weighted and gadolinium-enhanced spin-echo and 3DFT-CISS imaging.

PURPOSE To assess the value of unenhanced T1-weighted images, T2-weighted images, gadolinium-enhanced T1-weighted images, and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) images in depicting lesions of the membranous labyrinth.

METHODS Six patients were studied using 1-T MR; both enhanced (gadolinium-tetraazacyclododecane tetraacetic acid) and unenhanced images were obtained and different sequences compared to determine which provided the most information.

RESULTS A combination of gadolinium-enhanced T1-weighted and 3DFT-CISS images could depict all membranous labyrinth pathology. Unenhanced T1-weighted images were necessary to exclude spontaneous hyperintensity in the membranous labyrinth. Gadolinium-enhanced T1-weighted images were needed to detect enhancing pathology such as labyrinthitis and tumors inside the membranous labyrinth. In these cases, 3DFT-CISS images allowed immediate differentiation between inflammation and tumor. In temporal bone tumors involving the bony and membranous labyrinth, unenhanced and enhanced T1-weighted images often sufficed to suggest the correct diagnosis. Only 3DFT-CISS images were able to demonstrate small structures (as fistulas) and to help us confirm or rule out obliteration of the labyrinthine fluid spaces. 3DFT-CISS images were necessary to detect small congenital malformations of the membranous labyrinth when only MR was performed. Uncalcified obliteration of the labyrinth fluid spaces could be reliably detected only on 3DFT-CISS images. Here also gadolinium-enhanced T1-weighted images had to be obtained because enhancement of the soft tissues inside the membranous labyrinth had been observed.

CONCLUSION The CISS sequence and enhanced T1-weighted sequence formed the best sequence combination for diagnosis of membranous labyrinth lesions; additional, unenhanced T1-weighted images can help one differentiate labyrinthitis, proteinaceous fluid, subacute hemorrhage, or tumor inside the labyrinth.