Displacement of the facial nerve course by vestibular schwannoma: Preoperative visualization using diffusion tensor tractography

Abstract

Purpose: To preoperatively visualize the course of the facial nerve, which is displaced by vestibular schwannoma, using diffusion tensor (DT) tractography, and to evaluate the agreement with surgical findings. Materials and Methods:The subjects were eight patients with vestibular schwannoma who had undergone removal surgery. DT MR images were obtained and tracts that were considered to represent the facial nerve were constructed. We assessed the success rate for tract construction and evaluated the agreement between tractography findings and surgery. Results:We obtained a tract that connected the internal auditory meatus and brainstem, and was considered to represent the facial nerve in seven of eight cases. The course of the constructed tract agreed with surgical findings in five of these seven cases. One exception was a case in which the tumor was too large to enable intraoperative observation of the facial nerve; however, the facial nerve appeared to be displaced anteriorly at intracapsular resection, in agreement with tractography. In the other case, the schwannoma was mostly cystic. Conclusion:Tractographs constructed using MR tensor images enabled us to identify tracts considered to represent facial nerves. We consider DT tractography to be a useful tool for preoperatively predicting facial nerve displacement in vestibular schwannoma.

Tractography Delineates Microstructural Changes in the Trigeminal Nerve after Focal Radiosurgery for Trigeminal Neuralgia

“…The applicability of tractography to the study of cranial nerves is novel and few studies have been reported in this area [22], [23]. We recently demonstrated that tractography can be used to delineate the course of the cranial nerves, and that significant information with respect to the DTI parameters can be obtained [19], [24].…”

White matter tractography for neurosurgical planning: A topography-based review of the current state of the art

“…One of the major applications of WMT in skull base surgery is the preoperative identification of the facial nerve (FN) position, in patients harboring large vestibular schwannomas. We reviewed the existing literature comparing tractography predicted FN position with intraoperative findings (Table 6) (Gerganov et al, 2011, Song et al, 2016, Taoka et al, 2006, Wei et al, 2015, Zhang et al, 2013). FN tractography reconstruction was possible in 93% of the cases (71/76).…”

Imaging the Facial Nerve: A Contemporary Review

“…Both the facial nerve and the schwannoma have similar signal intensities, and larger tumors cause thinning of the facial nerve, making the nerve even more difficult to identify. Additionally, there is typically no intervening cerebrospinal fluid between the schwannoma and the facial nerve [2]. In these cases, diffusion tensor (DT) tractography may be useful for assessing facial nerve course and displacement.…”

“…Diffusion tensor (DT) tractography, which uses MRI to make three-dimensional (3D) reconstructions of the facial nerve, has recently been developed. This technique has been shown to be potentially useful in the identification displacement of cranial nerve fibers by vestibular schwannomas [2]. In all cases, choice of the imaging modality utilized should be determined by specifics of the patient's symptoms and the differential diagnosis.…”