Acknowledgement: Dr R Openshaw
Facial nerve monitoring
Neuromonitoring involves the continuous assessment of neural function during surgical procedures to enhance patient safety and improve outcomes. Facial nerve monitoring is a form of neuromonitoring used during surgical facial nerve procedures, such as vestibular schwannoma removal, to minimise the risk of facial nerve damage. This process consists of using specialised equipment to monitor the functional integrity of the facial nerve in real-time. Surgeons can detect electrical signals that indicate nerve activity by placing electrodes on the patient’s face. When the nerve is stimulated directly by surgical instruments or indirectly by the tumour, the electrodes pick up the resulting electrical responses. These signals are displayed on a monitor, allowing the surgical team to assess the nerve’s condition and make informed decisions to prevent injury.
The facial nerve
The facial nerve, or cranial nerve VII, is a vital structure that controls the muscles responsible for facial expressions. It also contributes to other functions, such as conveying taste sensations from the anterior two-thirds of the tongue and innervating certain glands, like the lacrimal (tear) and salivary glands. Originating in the brainstem, the facial nerve travels through two bony canals namely the internal auditory meatus and the facial nerve canal in the temporal bone, eventually branching out to innervate different areas of the face. Due to its proximity to various cranial structures, the facial nerve is highly susceptible to injury during surgeries, especially those involving the skull base, such as removing an acoustic neuroma.
The facial nerve and vestibular schwannoma
Acoustic neuromas, or vestibular schwannomas, are benign tumours that develop from the Schwann cells of the vestibular nerve, responsible for balance and hearing. Although these tumours are non-cancerous, they can grow in size and compress nearby structures, including the facial nerve. As the tumour expands, it can lead to facial weakness, paralysis, or other dysfunctions. Surgical removal is often necessary, mainly when the tumour is symptomatic or growing. However, the intricate anatomical relationship between the facial nerve and the tumor poses a significant challenge, making the preservation of the facial nerve a key concern during surgery.
How is facial nerve monitoring performed?
The process begins once the patient is placed under general anaesthesia, ensuring comfort and safety. An electrophysiologist, a specialist trained in the nervous system’s electrical activity, is responsible for monitoring.
The electrophysiologist inserts subdermal needles connected to electrodes into specific facial muscles—typically around the orbicularis oculi and orbicularis oris. These electrodes facilitate recording electrical activity within the facial nerve, allowing for real-time observation of nerve integrity. Throughout the procedure, the electrophysiologist meticulously monitors the recorded signals for any spontaneous compound action potentials (s-CAP) of the facial nerve. If the surgeon needs to assess the integrity and responsiveness of the facial nerve, it is stimulated, producing a triggered compound action potential (t-CAP), which the electrophysiologist communicates to the surgeon.
If the surgical technique inadvertently irritates the facial nerve, the electrophysiologist promptly alerts the surgeon, allowing immediate corrective measures to mitigate potential damage. This collaboration is vital for ensuring optimal surgical outcomes, as preserving facial nerve function is paramount. Facial nerve monitoring exemplifies the intersection of surgical precision and neuromonitoring, ultimately enhancing patient safety and promoting successful long-term results. The electrophysiologist’s role is essential, enabling a proactive approach to safeguarding the intricate pathways of facial nerve function.
Why use facial nerve monitoring?
The importance of facial nerve monitoring in acoustic neuroma removal cannot be overstated. During surgery, the proximity of the tumour to the facial nerve increases the risk of accidental nerve damage, which could lead to permanent facial paralysis, asymmetry, or loss of facial function. Such outcomes can significantly impact a patient’s quality of life, affecting their ability to express emotions, speak, or perform basic activities like eating and blinking. Facial nerve monitoring provides the surgical team with critical information about the nerve’s location and functional status, enabling them to navigate safely around it while removing the tumour.
In addition to preserving nerve function, facial nerve monitoring enhances surgical precision and reduces the likelihood of postoperative complications. Surgeons can avoid unnecessary dissection or trauma to surrounding tissues by identifying the nerve’s exact position. This is particularly important in cases where the tumour has caused the nerve to become stretched or displaced, making it more challenging to locate visually. The continuous feedback provided by monitoring systems ensures that any changes in nerve function are immediately detected, allowing the surgeon to adjust their approach accordingly.
Furthermore, facial nerve monitoring contributes to better long-term outcomes for patients. Studies have shown that intraoperative nerve monitoring significantly improves the chances of preserving facial nerve function after acoustic neuroma surgery. Postoperatively, patients who retain full or partial nerve function are less likely to experience complications like synkinesis (involuntary facial movements) or persistent weakness, leading to improved cosmetic and functional results.
A patient’s rights
Patients have the right to informed consent, which extends to discussing risks and benefits associated with surgical interventions, including the potential benefits of facial nerve monitoring. When healthcare providers choose not to utilise facial nerve monitoring in procedures where its application is standard or advisable, they may expose themselves to significant legal implications.
Failure to employ it can lead to preventable facial nerve injury, resulting in adverse outcomes such as paralysis or weakness. Should such complications arise, patients may pursue legal action under medical malpractice claims, arguing that the absence of facial nerve monitoring constitutes a breach of the standard of care. In legal terms, the standard of care is defined by what a similarly qualified practitioner would do under comparable circumstances. If it is established that nerve monitoring should be utilised based on prevailing medical guidelines or expert testimony, the omission may lead to liability for damages arising from negligent practice.
