MR Imaging of the Extracranial Facial Nerve with the CISS Sequence

Abstract

BACKGROUND AND PURPOSE: MR imaging is not routinely used to image the extracranial facial nerve. The purpose of this study was to determine the extent to which this nerve can be visualized with a CISS sequence and to determine the feasibility of using that sequence for locating the nerve relative to tumor. MATERIALS AND METHODS:Thirty-two facial nerves in 16 healthy subjects and 4 facial nerves in 4 subjects with parotid gland tumors were imaged with an axial CISS sequence protocol that included 0.8-mm isotropic voxels on a 3T MR imaging system with a 64-channel head/neck coil. Four observers independently segmented the 32 healthy subject nerves. Segmentations were compared by calculating average Hausdorff distance values and Dice similarity coefficients. RESULTS:The primary bifurcation of the extracranial facial nerve into the superior temporofacial and inferior cervicofacial trunks was visible on all 128 segmentations. The mean of the average Hausdorff distances was 1.2 mm (range, 0.3-4.6 mm). Dice coefficients ranged from 0.40 to 0.82. The relative position of the facial nerve to the tumor could be inferred in all 4 tumor cases. CONCLUSIONS:The facial nerve can be seen on CISS images from the stylomastoid foramen to the temporofacial and cervicofacial trunks, proximal to the parotid plexus. Use of a CISS protocol is feasible in the clinical setting to determine the location of the facial nerve relative to tumor.

On the usage of average Hausdorff distance for segmentation performance assessment: hidden error when used for ranking

“…In medical image segmentation, it is used to compare ground truth images with segmentation results and allows ranking different segmentation results. Average Hausdorff distance has been applied to assess performance of various applications including brain tumour segmentation [ 1 ], cerebral vessel segmentation [ 2 , 3 ], temporal bone segmentation [ 4 ], segmentation of the extracranial facial nerve [ 5 ], tumour volume delineation [ 6 ], colorectal liver metastases segmentation [ 7 ], prostate cancer lesion segmentation [ 8 ] and pylorus tracking on ultrasound images [ 9 ].…”

Seltene Erkrankungen der Speicheldrüsen und des Nervus Facialis

“…MRI visualizes the intracranial parts 220 and the temporal bone segments 221 . Conventional MR techniques only allow limited assessment of the extracranial part of the facial nerve 222 223 224 . However, single reports could already show that also these parts can be made visible 223 225 .…”

“…Conventional MR techniques only allow limited assessment of the extracranial part of the facial nerve 222 223 224 . However, single reports could already show that also these parts can be made visible 223 225 . The assessment of the intraparotideal course is difficult because the vascular structures in the parotid gland have a similar hypointensity on T2-weighted images 226 .…”

“…Mit der MR-Bildgebung lassen sich die intrakraniellen Anteile 220 und die Segmente im Felsenbein 221 visualisieren. Mit konventionellen MR-Techniken ist der extrakranielle Anteil des N. facialis nur begrenzt bewertbar 222 223 224 . Allerdings haben Einzelberichte schon gezeigt, dass auch diese Anteile sichtbar gemacht werden können 223 225 .…”

“…Mit konventionellen MR-Techniken ist der extrakranielle Anteil des N. facialis nur begrenzt bewertbar 222 223 224 . Allerdings haben Einzelberichte schon gezeigt, dass auch diese Anteile sichtbar gemacht werden können 223 225 . Die Bewertung des intraparotidealen Verlaufs ist schwierig, da die Gefäßstrukturen in der Glandula parotis auf T2-gewichteten Bildern eine ähnliche Hypointensität aufweisen 226 .…”