We compared the efficacy of eeDHFA and esHFA for the treatment of facial nerve injury during VS surgery and found that the outcome did not differ significantly between the two procedures. VS surgical techniques have improved with the rapid development of minimally invasive neurosurgery technology and electrophysiological monitoring. However, facial paralysis after VS surgery is common, and managing severe complications is still challenging. Hypoglossal-facial nerve anastomosis is one of the most effective methods for facial paralysis treatment after VS surgery . However, the traditional hypoglossal-facial nerve anastomosis technique involves complete transection of the hypoglossal nerve, leading to severe hemiglossal atrophy and speech, masticatory, and swallowing dysfunctions. Therefore, surgeons still need to develop new procedures capable of relieving the symptoms of facial paralysis and reducing the corresponding complications after nerve anastomosis to improve the patient’s quality of life.
Several improved surgical methods have been developed to avoid the complications associated with classic facial nerve and hypoglossal nerve trunk end-to-end anastomosis, including esHFA, masseteric-facial nerve anastomosis, end-to-end facial nerve anastomosis with interposition graft, and split hypoglossal-facial nerve anastomosis [2, 4–6, 11–18]. However, the key feature of an improved technique is that the procedure minimizes disruption of the hypoglossal nerve and other nerve functions, allowing for effective facial reanimation . Unfortunately, some of the surgical methods listed above are unlikely to achieve this outcome. The function of masseteric and interposition graft nerves is damaged during masseteric-facial nerve anastomosis and end-to-end facial nerve anastomosis with interposition graft. Furthermore, the interposition nerve graft needs two connecting points, which could reduce axon regeneration [11, 15]. Split hypoglossal-facial anastomosis causes injury to nerve axons , and splitting the hypoglossal nerve is technically difficult .
Many studies have demonstrated the effectiveness of esHFA [7, 10, 14, 19, 28–32]. Notably, a study by Samii and colleagues reported that the outcomes for facial function after esHFA and after classic end-to-end hypoglossal-facial nerve anastomosis were comparable, and that postoperative hemi-tongue atrophy could be avoided when esHFA was performed. However, this procedure is technically difficult, requiring surgeons to drill into the mastoid process and expose the mastoid part of the facial nerve.
The descending branch of the hypoglossal nerve, also known as the superior root of the ansa cervicalis, originates from the anterior branch of the first cervical nerve and accompanies the hypoglossal nerve to form the ansa cervicalis with fibers from the anterior branches of the second and third cervical nerves (the lower root of the ansa cervicalis). The main function of the ansa cervicalis is to lower the hyoid bone and to assist in swallowing and phonation. Owing to the compensatory effect of the inferior root of the ansa cervicalis, there was no obvious dysfunction after transecting the descending branch of the hypoglossal nerve. Moreover, the descending branch of the hypoglossal nerve is located in the surgical field during nerve anastomosis, making it easy to access. Therefore, this branch is a good choice for donor .
Transection of the main trunk of the hypoglossal nerve leads to unilateral lingual muscle atrophy and may result in dysphagia and difficulty in articulation and mastication . Use of the descending branch of the hypoglossal nerve as donor avoids these problems, potentially improving the quality of life of the patient. However, early reports suggested a poor outcome after eeDHFA [2, 12, 20]. Samii and Matthies reported that matching the diameters of the donor and recipient nerves is a key factor for successful nerve reanimation . Thus, some authors have suggested that the poor outcomes are the result of the significant mismatch in the fascicular surface area between the descendens hypoglossi and facial nerve, given that the former has only 20% of the fascicular surface area of the latter. This mismatch limits the use of the descendens hypoglossi for facial reanimation [2, 12, 20]. Further, some authors believe that the caudal-to-rostral direction of nerve impulse transmission in the superior root of the ansa cervicalis explains the poor results of eeDHFA for the treatment of facial palsy sequelae. However, others have reported good outcomes despite using the descendens hypoglossi as the donor nerve [2, 22, 23].
We performed eeDHFA when the diameter of the descending branch of the hypoglossal nerve was more than half of the facial nerve diameter. After follow-up, the outcomes for eeDHFA were as good as those for esHFA. In addition, surgical complications were avoided by performing eeDHFA. Only one patient from each group experienced hemi-tongue myoparalysis in this study. None of the patients developed postoperative dysphagia or hoarseness. Facial nerve anastomosis of the descending branch of the hypoglossal nerve is an improvement on facial nerve-hypoglossal nerve trunk end-to-end anastomosis, as the former preserves the hypoglossal nerve trunk and restores the facial nerve. The procedure could substantially reduce the incidence of complications, including unilateral tongue muscle atrophy and dysphonia. Moreover, it is a simple and efficient method for facial reanimation.
Given the impact of Wallerian degeneration, most authors concluded that the time elapsed between facial nerve injury and anastomosis has an important effect on facial reanimation outcomes [8, 10, 19, 34–36]. Darrouzet and colleagues reported that the recovery time for facial nerve function was extended in patients with a prolonged interval between facial injury and reanimation . Further, some authors suggest that muscle transfers, transposition or neuromuscular pedicle grafts, and facial nerve repair should all be performed when paralysis has been present for more than 2 years, due to the progression of facial muscle atrophy [37–39]. Importantly, most authors report that facial repair should be performed within 2 years to ensure good recovery of facial nerve function [4, 14]. We believe that the effect of surgical timing on facial recovery is minimal when the pre-repair interval is less than 2 years. In addition, it is important to note that the myelinated axons of the injured facial nerve are likely to degenerate and decrease in number. It has been reported that the diameter of an intact facial nerve is approximately 61.5% of the normal hypoglossal nerve diameter, whereas this figure becomes less than 50% in case of nerve injury . We believe that the matching between the descendens hypoglossi and facial nerve was an important factor behind the outcomes we observed in this study.
The eeDHFA and esHFA procedures are effective for the treatment of facial paralysis after VS removal and result in improved facial symmetry, facial muscle tension, and motor function. Samii and colleagues reported that the best results were observed in patients with VS, while the worst outcomes occurred in the “other pathology” group (p=0.038) . Therefore, further research is needed to investigate the efficacy of eeDHFA in patients with diseases other than VS. Additional studies are also required to determine the optimal diameter of the descending branch of the hypoglossal nerve and to clarify the mechanism of nerve reanimation. In addition, the data of this study were collected retrospectively from records, and the sample was small. Thus, the efficacy of eeDHFA should be studied further in a prospective study.