Hypoglossal Nerve Transfer: A Comprehensive Guide

Today, there are many treatment methods for facial paralysis. One of these treatment methods is hypoglossal nerve transfer surgery. This procedure is generally performed on individuals who have suffered from long-term facial paralysis and provides permanent results. If you would like to learn more about this procedure, please take a look at our content. We wish you all happy reading and healthy days.

What is Hypoglossal Nerve Transfer?

Hypoglossal nerve transfer is a surgical procedure in which the motor fibers of the hypoglossal nerve (12th cranial nerve) are surgically connected to the facial nerve (7th cranial nerve) in order to re-stimulate the facial nerve, which has lost its function, in cases of long-term or permanent facial paralysis. This method is preferred, especially in cases of paralysis following tumor surgery, trauma, or advanced nerve damage, where primary repair of the facial nerve is not possible. Thus, since the hypoglossal nerve is a strong motor nerve, it provides sufficient axonal support to the facial muscles, initiating the reinnervation process.

This procedure is performed under a surgical microscope and can be applied using end-to-end, end-to-side, or partial (split) techniques. The aim is to improve resting symmetry in the facial muscles and restore voluntary muscle movements; although a complete return to natural facial expressions is not always possible, significant functional and aesthetic improvement can be achieved.

Who is a Good Candidate for Hypoglossal Nerve Transfer?

We can say that suitable candidates for hypoglossal nerve grafting are generally patients with the following characteristics:

• Patients with long-term peripheral facial paralysis – Cases where the facial nerve is unlikely to heal on its own.

• Patients for whom primary repair of the facial nerve is not possible – Following trauma, tumor surgery, or severe nerve loss.

• Facial paralysis cases developing after acoustic neuroma surgery – Especially if the nerve has not been preserved or has been damaged.

• Patients experiencing permanent facial paralysis – Those who have had loss of facial movement for 12–18 months or longer.

• Individuals without severe atrophy of the facial muscles – Muscle tissue must still be capable of responding to reinnervation.

• Patients whose general health is suitable for surgery – Individuals who can tolerate the risks of anesthesia and surgery.

• No age restrictions, but higher success rates in younger and middle-aged groups – Nerve recovery may slow with age.

In Which Cases Is Hypoglossal Nerve Transfer Performed?

There are certain situations in which hypoglossal nerve transfer is performed. These situations are generally as follows:

• Long-term or permanent facial paralysis – When the facial nerve has a low chance of healing on its own.
• Cases where primary repair of the facial nerve is not possible – Following trauma, tumor surgery, or severe nerve damage.
• Facial paralysis following acoustic neuroma surgery – In cases where the nerve could not be preserved or was damaged after acoustic neuroma treatment.
• Traumatic facial nerve injuries – When facial muscle function is lost.
• Permanent paralysis following Guillain-Barré Syndrome or other peripheral neuropathies – When facial nerve function loss persists.
• To regain facial muscle function – To correct resting asymmetry and restore voluntary facial movements.

How is Hypoglossal Nerve Transplantation Performed?: Step-by-Step

Contrary to popular belief, the hypoglossal nerve transfer procedure is a relatively simple and quick surgical process. If we break down this process step by step, it is as follows:

1. Detailed Clinical and Electrophysiological Evaluation

• The duration, severity (House-Brackmann classification), and progression of facial paralysis are analyzed.
• The potential for muscle reinnervation is assessed using EMG.
• The anatomical integrity of the facial nerve is examined using imaging (MRI).
• It is determined whether muscle atrophy is irreversible.

2. Surgical Planning and Technique Selection

• A decision is made as to which of the end-to-end, end-to-side, or partial (split) hypoglossal transfer options is appropriate.
• The priority of preserving tongue function is evaluated.
• If necessary, an interposition graft (nerve graft) is planned.

3. Anesthesia and Positioning

• The procedure is performed under general anesthesia.
• The patient is placed supine, with the head fixed in a slight rotation to the opposite side.
• The surgical site is prepared with antiseptic solutions.

4. Surgical Approach and Exploration of Nerves

• An incision is made covering the area behind the ear and the upper cervical region.
• The facial nerve is dissected from the mastoid segment or at the level of the stylomastoid foramen.
• The hypoglossal nerve is carefully dissected in the vicinity of the carotid sheath.
• The surrounding vascular structures are preserved.

5. Preparation of Nerves

• The distal segment of the facial nerve is prepared down to the living tissue.
• The appropriate segment of the hypoglossal nerve is selected.
• If the partial technique is to be used, a certain percentage of the nerve is separated; if the total technique is to be used, a complete transection is performed.

6. Microneurosurgical Anastomosis

• Nerve endings are aligned without tension under a surgical microscope.
• Epineural anastomosis is performed using 9-0 or 10-0 monofilament sutures.
• If necessary, it is reinforced with fibrin glue.
• The goal is to achieve proper alignment that will allow for optimal axonal passage.

7. Hemostasis and Closure

• Bleeding is controlled.
• A drain is placed if deemed necessary.
• The layers are closed anatomically.

8. Postoperative Follow-up and Rehabilitation

• In the early days, speech movements and swallowing function are assessed.
• The reinnervation process begins on average within 3–6 months.
• A neuromuscular re-education program for facial muscles is initiated.
• The final functional assessment is performed at 12–18 months.

The Effect of Hypoglossal Nerve Transfer Surgery on Facial Paralysis

Hypoglossal nerve transfer surgery is a reconstructive procedure that aims to achieve meaningful functional and aesthetic improvement by re-innervating facial muscles in cases of long-term or permanent peripheral facial paralysis. In this procedure, the powerful motor axons of the hypoglossal nerve are redirected to the facial nerve, initiating the reinnervation process in the denervated facial muscles. After the procedure, significant improvement can be achieved, particularly in resting facial asymmetry; the drooping of the corner of the mouth is reduced and facial tone increases. Over time, patients may gain voluntary facial movements, but these movements may initially be synchronized with tongue movements and require neuromuscular retraining.

In this context, the effectiveness of surgery is directly related to the duration of paralysis, the viability of muscle tissue, the technique used (partial or total transfer), and the quality of the rehabilitation process. When appropriate patient selection is made, hypoglossal nerve transfer offers a powerful and sustainable functional restoration option in permanent facial paralysis.

Advantages of Hypoglossal Nerve Transfer Procedure

The hypoglossal nerve transfer procedure provides physical and psychological benefits to the individual. These benefits are as follows:

• Provides a strong motor nerve source – The hypoglossal nerve has a high axon density, providing effective reinnervation support to the facial muscles.
• It is a permanent reconstruction method – Once the nerve connection is established, the resulting muscle activity persists long-term.
• It is an effective option for long-term facial paralysis – It can be applied in cases where primary nerve repair is not possible or in delayed cases.
• It significantly improves resting symmetry – Mouth corner drooping and facial sagging decrease, and facial tone increases.
• It can be performed as a single-stage surgery – In most cases, no additional sessions are required.
• Tongue function can be preserved with partial techniques – Speech and swallowing functions are largely preserved thanks to the split hypoglossal method.
• Can be combined with other reconstructive methods – If necessary, it can be planned in conjunction with masseteric nerve transfer or cross-facial nerve grafting.
• Provides functional and aesthetic benefits – Improves both facial movements and the quality of social interaction.

Recovery Process After Hypoglossal Nerve Transfer

The recovery process following hypoglossal nerve transfer is based on a gradual and biologically time-consuming reinnervation process. In this context, mild edema, sensitivity, and temporary neck stiffness related to the surgical site may be observed in the first weeks after surgery; if a partial technique is used, tongue functions are generally preserved, while mild tongue weakness may occur in total transfers. On the other hand, the actual recovery begins with the progression of axons from the hypoglossal nerve to the facial muscles via the facial nerve; this process becomes clinically noticeable within an average of 3–6 months with the observation of the first muscle contractions.

Initially, movements may be weak and voluntary control limited; even synchronous contractions with tongue movements may be observed. Therefore, neuromuscular re-education, mirror therapy, and facial exercises are critically important. Within 9–12 months, muscle strength increases, resting symmetry improves significantly, and more controlled facial movements develop. The final functional assessment is usually performed at 12–18 months. The quality of the outcome is directly related to the duration of paralysis, the degree of muscle atrophy, the surgical technique used, and compliance with the rehabilitation process.

Results and Outcomes of Hypoglossal Nerve Transfer

The results and effects of hypoglossal nerve transfer aim to provide meaningful improvements in both functional and aesthetic aspects in cases of long-term facial paralysis. Post-surgery, motor fibers from the hypoglossal nerve re-stimulate the facial muscles via the facial nerve, leading to an increase in muscle tone over time and a significant reduction in resting facial asymmetry. In particular, improvement in the drooping of the corner of the mouth and a more balanced appearance in the lower part of the face are achieved. As the reinnervation process is completed, patients can gain voluntary facial movements; however, these movements may initially be related to tongue activity and require neuromuscular adaptation.

Additionally, while the complete return of natural and spontaneous facial expressions is not always possible, dynamic movements that support social communication improve significantly in most patients. The surgical technique used, the duration of paralysis, the viability of muscle tissue, and compliance with the rehabilitation process directly affect the quality of the outcome.

Comparing Treatment Options: Hypoglossal vs. Gracilis Free Tissue Transfer

Although hypoglossal nerve transfer and gracilis free tissue transfer are often compared to each other, there are significant differences between them. These differences are as follows:

• Hypoglossal nerve transfer aims to restore function by re-stimulating existing facial muscles, while gracilis free flap transfer involves transplanting new muscle tissue taken from the thigh to replace non-functioning muscles.
• Hypoglossal transfer is generally preferred when facial muscles retain their vitality and facial nerve function is lost, while gracilis transfer is performed in cases of long-term paralysis and in patients with significant muscle atrophy.
• Hypoglossal nerve transfer is performed through a single surgical site, whereas gracilis transfer involves surgery on both the facial region and the thigh (donor site).
• Hypoglossal transfer is technically a shorter and less complex operation; gracilis free tissue transfer is longer and more complex because it requires microsurgical vessel and nerve anastomoses.
• Hypoglossal transfer strongly corrects resting symmetry and provides voluntary movement; gracilis transfer, especially when combined with a suitable nerve source, may offer a more natural and spontaneous smile potential.
• Initial synchronization between tongue and facial movements may be observed after hypoglossal transfer; gracilis transfer requires more intensive rehabilitation for functional adaptation of the new muscle.
• Tongue function is largely preserved when partial techniques are used in hypoglossal transfer; gracilis transfer carries an additional risk of morbidity depending on the donor site.

If you would like detailed information about hypoglossal nerve transfer, you can contact Dr. Berke Özücer and his team, who specialize in facial paralysis.