Spatial relationship between vestibular schwannoma and facial nerve on three-dimensional T2-weighted fast spin-echo MR images

BACKGROUND AND PURPOSE: During surgical removal of a vestibular schwannoma, correct identification of the facial nerve is necessary for its preservati on and continuing function, We prospectively analyzed the spatial relations hip between vestibular schwannomas and the facial nerve using 3D T2-weighte d and postcontrast T1-weighted spin-echo (SE) MR Imaging. METHODS. Twenty-two patients with a unilateral vestibular schwannoma were e xamined with MR imaging, The position and spatial relationship of the facia l nerve to adjacent tumor within the internal auditory canal (IAC) and cere bellopontine angle cistern (CPA) were assessed on multiplanar reformatted 3 D T2-weighted fast spin-echo (FSE) images and on postcontrast transverse an d coronal T1-weighted SE images. The entrance of the nerve into the bony ca nal at the meatal foramen and the nerve root exit zone along the brain stem were used as landmarks to follow the nerve course proximally and distally on all images. RESULTS: The spatial relationship between vestibular schwannoma and facial nerve could not be detected on postcontrast T1-weighted SE images. In 86% o f the patients, the position of the nerve in relation to the tumor was disc ernible on multiplanar reformatted 3D T2-weighted PSE images, In tumors wit h a maximal diameter up to 10 mm, the entire nerve course was visible; in t umors with a diameter of 11 to 24 mm, only segments of the facial nerve wer e visible; and in tumors larger than 25 mm, the facial nerve could not be s een, owing to focal nerve thinning and obliteration of landmarks within the IAC and CPA. CONCLUSION: Identification of the facial nerve and its position relative to an adjacent vestibular schwannoma is possible on multiplanar reformatted 3 D T2-weighted FSE images but not on postcontrast T1-weighted SE images. Det ection of this spatial relationship depends on the tumor's size and locatio n.