Parotid gland tumours: MR tractography to assess contact with the facial nerve
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To assess the feasibility of intraparotid facial nerve (VIIn) tractographic reconstructions in estimating the presence of a contact between the VIIn and the tumour, in patients requiring surgical resection of parotid tumours.
Patients underwent MR scans with VIIn tractography calculated with the constrained spherical deconvolution model. The parameters of the diffusion sequence were: b-value of 1000 s/mm2; 32 directions; voxel size: 2 mm isotropic; scan time: 9’31’. The potential contacts between VIIn branches and tumours were estimated with different initial fractional anisotropy (iFA) cut-offs compared to surgical data. Surgeons were blinded to the tractography reconstructions and identified both nerves and contact with tumours using nerve stimulation and reference photographs.
Twenty-six patients were included in this study and the mean patient age was 55.2 years. Surgical direct assessment of VIIn allowed identifying 0.1 as the iFA threshold with the best sensitivity to detect tumour contact. In all patients with successful VIIn identification by tractography, surgeons confirmed nerve courses as well as lesion location in parotid glands. Mean VIIn branch FA values were significantly lower in cases with tumour contact (t-test; p ≤ 0.01).
This study showed the feasibility of intraparotid VIIn tractography to identify nerve contact with parotid tumours.
• Diffusion imaging is an efficient method for highlighting the intraparotid VIIn.
• Visualization of the VIIn may help to better manage patients before surgery.
• We bring new insights to future trials for patients with VIIn dysfunction.
• We aimed to provide radio-anatomical references for further studies.
KeywordsDiffusion tractography Parotid gland Facial nerve Magnetic resonance imaging Salivary gland neoplasms
Diffusion tensor imaging
Constrained spherical deconvolution
Balanced fast field echo
Region of interest
Facial nerve division
Orientation density function
Signal to noise ratio
Internal auditory canal