HIGH-RESOLUTION MR OF THE INTRAPAROTID FACIAL-NERVE AND PAROTID DUCT

PURPOSE: To describe a high-resolution MR imaging technique that depic ts the complex anatomy of the region of the parotid gland, focusing on the intraparotid components of the facial nerve and parotid duct. MET HODS: High-resolution TI-weighted images of the parotid gland were acq uired with a prototype three-dimensional Fourier transform gradient-ec ho sequence that permits a very short echo time (4.2 milliseconds) by using a modified phase-encoded time-reduced acquisition scheme. The se quences were obtained at 1.5 T with a head and neck coil. Postprocesse d multiplanar, curved and volumetric images were obtained. The most cl inically useful images were acquired at parameters of 30/4.2 (TR/TE(ef f)) a flip angle of 30 degrees, a field of view of 18 to 20 cm, a matr ix of 512x288 or 512x256, an axial plane, 60 images, no gaps, and a se ction thickness of 1.5 mm. Eighteen healthy subjects were examined. Th e position of the facial nerve within the parotid gland was determined by identifying the facial nerve in the stylomastoid foramen and then following it on sequential sections through the parotid gland. Curved reformations were used to confirm the visibility of the nerve. A simil ar technique was used for the parotid duct. RESULTS: The image contras t obtained was similar to that of standard spin-echo T1-weighted image s. The parotid gland showed intermediate signal intensity while the fa t spaces showed high signal signal intensity. The vessels had variable signal intensity depending on saturation. The cerebrospinal fluid, ne rves, muscles, and ducts had lower signal intensity. In all 18 subject s, the facial nerve from the brain stem to the parotid gland, and the parotid duct from the mouth to the hilus of the gland were seen bilate rally. The proximal intraparotid facial nerve to the level of the retr omandibular vein was seen in 72% of the subjects and the main intrapar otid ducts were seen in 66% of the subjects. CONCLUSION: High-resoluti on MR imaging offers simultaneous display of most of the important str uctures in the region of the parotid gland, including the intraparotid duct and facial nerve.