Intra-parotid Facial Nerve Imaging in Parotidectomy

Surgical removal of tumors arising from the parotid gland (benign or malignant) is treatment of choice. However, the most detrimental complication of parotidectomy is facial weakness or facial nerve palsy, because the facial nerve crosses in the mid-portion of the parotid gland. Numerous studies indicated the incidence of temporary facial weakness as 5-45% and permanent facial palsy as 0-15% after parotidectomy. To reduce this complication, the investigators will apply the modern technique of MRI imaging to inform the anatomical relationship between the tumor and the facial nerve within the parotid gland preoperatively. Three dimensional double echo steady state MRI imaging (3D-DESS MRI) has been reported useful for the intra-parotid facial nerve imaging. Thus, the investigators will evaluate the clinical usefulness of 3D-DESS MRI for functional preservation of the facial nerve during parotidectomy. Preoperative 3D-DESS MRI imaging can provide information about the anatomical relationship between the tumor and the facial nerve in the parotid gland. In the retrospective series, the investigators found that there were 25.6% temporary facial weakness and 10.3% permanent (\> 6 months) facial weakness after parotidectomy for deep-seated parotid tumors (plus tumors located in both deep and superficial parotid gland); whereas 6.7% and 3.6% facial weakness respectively for superficially located parotid tumors. Because the risk of postoperative facial weakness is relatively high in the deep-seated parotid tumors, the investigators will exclude the patients with the superficial parotid tumors (determined by preoperative CT or US) and only include the patients with deep seated parotid tumors in this trial. The main outcome of our study is the incidence of immediate postoperative facial weakness, and the secondary outcome is the incidence of facial weakness at postoperative 6 months.