Facial Nerve Electromyographic Monitoring - An Overview

Introduction

Facial nerve electromyographic monitoring, also known as facial nerve monitoring (FNM), is a technique used to monitor the facial nerve's function during surgeries that may affect the nerve. This technique involves the placement of electrodes on the face to measure the electrical activity of the facial muscles, which is then used to assess the function of the facial nerve.

What Is a Facial Nerve?

The facial nerve, also known as the seventh cranial nerve, is a nerve that originates in the brainstem and extends through the skull to innervate the muscles of the face. It is responsible for controlling the movement of the muscles in the face, including those involved in facial expressions, as well as the muscles involved in taste sensation and the production of saliva and tears. The facial nerve is a mixed nerve, meaning it contains sensory and motor fibers. The sensory fibers of the facial nerve are responsible for transmitting taste sensations from the front two-thirds of the tongue and providing some sensory input to the ear. The facial nerve's motor fibers innervate the facial muscles, including those involved in raising the eyebrows, closing the eyes, smiling, and frowning. Damage to the facial nerve can impact a person's quality of life and cause paralysis of the facial muscles.

What Condition Required Facial Nerve Monitoring?

Facial nerve monitoring may be required during surgical procedures that can potentially damage the facial nerve. Some examples of such surgeries include:

• Parotid Gland Surgery: The parotid gland is a salivary gland located in the cheek. Surgery to remove a tumor or treat an infection in the gland can damage the facial nerve.

• Middle Ear Surgery: Surgery to treat conditions such as cholesteatoma (cyst-like growth behind eardrum) or otosclerosis (abnormal bone growth within middle ear) can damage the facial nerve.

• Brain Surgery: Some brain surgeries, such as those performed to remove a tumor or to treat epilepsy, may involve the facial nerve.

• Facial Plastic and Reconstructive Surgery: Procedures to correct facial paralysis or deformities may involve the facial nerve.

Why Is Facial Nerve Monitoring Necessary?

The facial nerve is responsible for the movements of the muscles in the face, including those involved in expressions such as smiling, frowning, and blinking. During certain surgeries, such as those involving the ear, parotid gland, or brain, the facial nerve may be at risk of damage. Destruction to the facial nerve can cause temporary or permanent facial weakness, which can greatly impact a patient's quality of life. Facial nerve monitoring helps prevent such damage by allowing the surgeon to monitor the function of the nerve in real time during the surgery.

How Does Facial Nerve Monitoring Work?

Facial nerve monitoring works by measuring the electrical activity of the facial muscles in response to stimulation of the facial nerve. The monitoring system consists of electrodes placed on the face to detect and record the electrical signals produced by the facial muscles.

During surgery, the surgeon may stimulate the facial nerve to check its function. The stimulation can be done in various ways, such as by applying a small electric current to the nerve or tapping it. The electrical signals produced from the facial muscles in response to the stimulation are recorded by the electrodes and displayed on a monitor. The monitoring technician analyzes the signals to determine if the facial nerve is functioning normally. If the signals indicate that the nerve is not functioning properly, the surgeon can adjust their approach to avoid or minimize any potential damage to the nerve. For example, they may adjust the position of a surgical instrument or use a different surgical technique to avoid putting pressure on the nerve.

• Electromyography (EMG): EMG involves placing electrodes on the facial muscles to detect their electrical activity. During surgery, the surgeon can stimulate the facial nerve, and the EMG electrodes will detect the electrical signals produced by the facial muscles in response to the stimulation. The signals are displayed on a monitor and analyzed by the monitoring technician to determine if the facial nerve is functioning normally.

• Electroneurography (ENoG): ENoG involves placing electrodes on the skin over the facial nerve and measuring the electrical signals produced by the nerve. During surgery, the surgeon can stimulate the facial nerve, and the ENoG electrodes will detect the electrical signals produced by the nerve. The signals are displayed on a monitor and analyzed by the monitoring technician to determine if the facial nerve is functioning normally.

• Brainstem Auditory Evoked Potential (BAEP) Monitoring: BAEP involves placement of electrodes on the scalp and electrical activity is measured present in response to sounds. During surgery, the surgeon can stimulate the facial nerve, and the BAEP electrodes will detect the electrical signals produced by the brainstem in response to the stimulation. The signals are displayed on a monitor and analyzed by the monitoring technician to determine if the facial nerve is functioning normally.

What Are the Benefits of Facial Nerve Monitoring?

Facial nerve monitoring provides several benefits during surgery, including:

• Facial nerve monitoring allows for the early detection of any damage to the facial nerve during surgery. This will make the surgeon take prompt corrective action to prevent or minimize nerve damage.

• By minimizing the risk of damage to the facial nerve during surgery, facial nerve monitoring can help in improvement of surgical outcomes and thus decrease the risk of complications.

• If the monitoring system detects a problem with the facial nerve function, the surgeon can adjust their surgical approach to minimize the risk of further nerve damage. For example, they may use a different surgical technique or instrument to avoid putting pressure on the nerve.

• By minimizing nerve damage during surgery, facial nerve monitoring can reduce the recovery time for patients and improve their quality of life.

• While facial nerve monitoring adds a cost to the surgical procedure, it can be cost-effective in the long run by reducing the risk of complications and the need for additional surgeries or treatments.

Conclusion

Facial nerve monitoring is an essential technique used during surgical procedures that involve the facial nerve. It provides a real-time assessment of facial nerve function, allowing immediate corrective action to prevent or minimize nerve damage. The use of facial nerve monitoring can improve surgical outcomes, reduce the risk of complications, and ultimately lead to better patient outcomes.