Trigeminal Neuralgia (TN), often times referred to as Tic Douloureux, is a disorder characterized by repeated episodes of severe facial pain. The pain can be localized over either side of the face and affects one or more of the divisions of the trigeminal nerve. This nerve, which gives rise to sensation within the face, originates in the brainstem and reaches the cavernous sinus through a structure called Meckel’s cave. In the cavernous sinus, the trigeminal nerve divides into three branches, termed the 1st, 2nd and 3rd branches, or ophthalmic, maxillary and mandibular nerves, respectively.

These nerve branches leave the intracranial (brain) cavity through separate exits, the superior orbital fissure and the foramen ovale and rotundum, and travel to innervate and give sensation to different areas of the face. TN usually affects one or two branches of the trigeminal nerve and is characterized by sudden, sharp paroxysms of “lancinating” pain.

This intense pain is described as a superficial electrical sensation and can be triggered by touching specific skin areas (trigger points) with cold air or activities like chewing, talking, swallowing, etc. Because chewing precipitates attacks, it is not uncommon for TN patients to lose weight.

What is typical and atypical Trigeminal Neuralgia?

In typical TN, patients suffer from unpredictable electric-like lancinating pains that are episodic and felt in a constant facial location. Affected patients can consistently reproduce an attack by touching a skin “trigger point” on the skin or performing a specific activity like chewing or talking.

In cases of atypical TN, the pain is characterized by a persistent dull aching or burning sensation localized to a more diffuse region of the face. Paroxysms of pain can complicate atypical TN resulting in some measure of baseline discomfort. There is usually not a specific trigger point with atypical TN.

TN is more common in women and is much more typically seen during the middle or later years of life. The unpredictable nature of such severe lancinating pain makes it emotionally incapacitating and produces a disruptive effect on a patient’s quality of life.

What is the cause of Trigeminal Neuralgia?

TN is usually related to the chronic compression of the trigeminal nerve by a blood vessel (usually an artery, occasionally a vein). Arterial rhythmic pulsations are a normal effect of the pressure wave produced by the heart.

This pressure wave from the heart is propagated throughout the vascular system when blood is pumped into the aorta, and from there, into all the arteries of the body. In some people, if a brain artery is very close to a nerve, its rhythmic pulsation can irritate the nerve and produce abnormal nerve signals.

Since the trigeminal nerve is anatomically close to the superior cerebellar artery, contact between the two structures sometimes permits arterial beating to short circuit nerve impulses and thereby result in trigeminal neuralgia.

The primary support for this theory is provided by the fact that moving the artery away from the nerve through an operation called Microvascular Decompression (MVD) produces immediate pain relief in up to 80% of the patients.

What is the natural history of Trigeminal Neuralgia?

Typical TN has a sudden onset and can last several years and even decades. The number of attacks can be seasonal and vary from many per day to a few per year. Spontaneous resolution is rare. Atypical TN is characterized by a slow and gradual worsening of facial pain.

What are the treatment options for Trigeminal Neuralgia?

Over the years, numerous medical and surgical treatments have been offered to TN patients with varying degrees of success. Medications, such as dilantin, tegretol and neurontin, have the ability to stabilize nerve cell membranes and relieve pain in most patients. However, these medications are not always effective, and can produce fatigue or other significant side-effects in some patients. Nevertheless, such medications are generally the first line of treatment.

Patients that fail multiple medical trials are offered surgical treatment ranging from peripheral ablative (destructive) procedures to an open “craniotomy” for microvascular decompression (MVD). In the youngest patients, the most invasive operation, an MVD, is often preferred because it holds the potential of long-term cure without causing significant facial numbness.

Meanwhile, radiofrequency (thermal) rhizotomy, glycerol rhizotomy or nerve balloon compression are all ablative procedures that attempt to destroy, in a minimally invasive fashion, the trigeminal pain fibers that cause pain. However, these operations have variable degrees of success, and relief oftentimes does not last more than a few years (1-5 yrs). Therefore, treatment is typically repeated several times over a patient’s lifetime.

Furthermore, all such operations are invasive and carry with them the inherent risks of infection, arterial or cranial nerve injury, or even stroke. Certain patients have medical contraindications that preclude any invasive operation, while still others may choose for personal reasons to avoid invasive surgery.

CyberKnife radiosurgery for Trigeminal Neuralgia

Radiosurgery is the newest treatment for TN. This non-invasive procedure is based on the concept that very many focused beams of radiation can be precisely targeted onto the trigeminal nerve and used to administer an ablative dose of energy.

In effect, one can “cut” pain fibers with radiosurgery. Initially, such treatment was administered only with frame-based radiosurgical technologies, such as the Gamma Knife and Linac-based systems. These procedures all require that a metal “stereotactic” ring be attached to the patient’s skull under local anesthesia. However, the CyberKnife has recently emerged as an effective and safe radiosurgical alternative for TN patients. In contrast to other forms of radiosurgery, the CyberKnife does not require a painful stereotactic frame to be attached to a patient’s skull.

There is actually no pain whatsoever with CyberKnife radiosurgery. CyberKnife radiosurgical treatment has been demonstrated to be as accurate and precise as frame-based systems with the added benefit of enhanced patient convenience and comfort.

How does the CyberKnife work?

The process of treating TN with the CyberKnife begins with a very high resolution CT scan of the brain, and in particular, the immediate vicinity of the trigeminal nerve. To optimally visualize the trigeminal nerve, a radio-opaque iodinated dye (or contrast) agent called metrizamide is often injected into the spinal fluid through a spinal tap.

Such metrizamide-enhanced CT scan imaging shows the trigeminal nerve in great detail. Alternatively, the treating neurosurgeon can visualize the trigeminal nerve with an MRI scan, and then use a computer to merge (fuse) the MRI and CT scans with one another. Regardless, the purpose of imaging is to visualize the trigeminal nerve in as much detail as possible so that an extremely accurate customized treatment plan can be created.

During the actual CyberKnife treatment, a focused high intensity beam of radiation is precisely targeted along a segment of the trigeminal nerve, beginning from a point 2-3 mm from its brainstem origin to the entry into Meckel’s cave.

Throughout treatment, a patient’s smallest head movements are detected and accurately compensated for by the controlling computer. A single CyberKnife treatment session for TN is completed in slightly over 1 hour.

How successful is CyberKnife radiosurgery for Trigeminal Neuralgia?

Up to 80% of TN patients treated with the CyberKnife will experience substantial and long lasting pain relief. The most common side-effect is an area of numbness over the face that probably correlates with the degree of pain relief.

The onset of pain relief after the CyberKnife may be substantially faster than with other forms of radiosurgery. This effect may be due to the increased accuracy of this procedure. Longer follow-up will be needed before it will be possible to estimate the duration of pain relief.

Nevertheless, it is clear that the painless CyberKnife procedure is a safe and effective treatment option for many patients with TN.