Areas of possible pain distribution according to the three branches of the trigeminal nerve
What is the trigeminal nerve?
The trigeminal nerve is a cranial nerve that provides the face with the sense of – touch, temperature and pain. The third branch of this nerve also provides motor function to the muscles of mastication. There are two trigeminal nerves serving the corresponding side of the face where they are located.
As the name of the nerve implies – it has three branches. The trigeminal nerve originates in the brain stem, at the base of the skull it divides into 3 branches that innervate the skin of the face. The first branch is responsible for sensation in the forehead and the region above the eye, the second branch is tasked with sensation in the upper jaw and the third branch deals with sensation in the lower jaw (please see picture above).
What is trigeminal neuralgia?
Patients describe trigeminal nerve pain (aka tic doloureux) as a sudden, electrical shock affecting one side of the face in a specific area. The patient is usually able to accurately pinpoint the area affected by the pain. The pain is usually jolt-like, shooting, sharp and intolerable. Generally, the pain is intermittent, meaningthat exacerbations, which tend to be more frequent in the autumn and spring season, are replaced by periods of remission when pain is minimal or at all absent. Such periods of remission may be several months long.. It should be noted that the longer a person suffers from trigeminal neuralgia, the shorter and more unstable the painless periods become.
Pain can be spread through the innervation area of a singleor several nerve branches, sometimes all branches are affected at the same time (please see picture). Pain is most often localized to the second and third branches of the nerve. Trigeminal nerve pain can, quite often, mimic toothache. It is often observed that several healthy teeth are extracted before a correct diagnosis is established.
Trigeminal nerve pain can be provoked, amongst other factors, by touch, talking, smiling, eating, brushing teeth, shaving, cold air and wind. Patients with a long history of illness develope guarding behaviours such as limiting facial movements, for example smiling, in the painful region, eating less or in a specific manner, avoiding touching of the face. Because of the aforementioned reasons trigeminal neuralgia is considered to be a debilitating disease, limiting simple daily activities due to the excruciating pain. The pain can frequently be severe enough to limit the working ability of patients.
The disease affects women more often than men, and although typically manifests between the ages 40-50 (4th-5th decade of life) is not limited to this age group, affecting younger patients as well.
Picture: n. trigeminus innervation (spread of pain) zones
What is the cause of trigeminal neuralgia?
A common misconception is that the nerve can be “frozen” or damaged by cold weather, and while it can of course be a provocative factor, it definitely isn’t the cause of the condition. In up to 80-90% of all cases, trigeminal neuralgia is caused by pressure of an adjacent blood vessel on the trigeminal nerve, a so-called neurovascular conflict. Both arteries and veins are located near the outlet of the trigeminal nerve in the vicinity of the brain stem. When one of the blood vessels, sometimes several, press on the trigeminal nerve, nerve injury occurs, which in turn manifests as a classic shooting, electrical facial pain.
Less commonly found causes for such symptoms, to name a few, are: a tumor pressing down on the trigeminal nerve, multiple sclerosis (which causes nerve damage) and of course – dental problems.
How is trigeminal neuralgia diagnosed?
One of the criteria for the diagnosis of trigeminal neuralgia is the character of the pain itself. This means that a comprehensive history of the patient, involving specifics of the pain, its nature, affected region and duration can be sufficient to raise the doctors suspicion of the diagnosis.
A specific magnetic resonance scan of the brain is needed to confirm the diagnosis. Images of an MRI scan can demonstrate if a nearby blood vessel is pressing down on the nerve. A diagnosis can be established if the patient has both of the following: typical symptoms and an established conflict between the nerve and the vasculature demonstrated by magnetic resonance imaging.
Sometimes the pain can be very typical of trigeminal neuralgia, but an MRI scan does not demonstrate any visible conflict between the nerve and surrounding vasculature. In that case, and if medical treatment options have been exhausted, the patient is offered surgery. During surgery, it is usually found, that there was in fact a blood vessel or scar tissue that was not visible on an MRI, compressing the nerve and causing pain.
Sometimes, MRI imaging for unrelated reasons shows that there is a neurovascular conflict, but patient does not have any complaints relating to the trigeminal nerve. In such a case there is no cause for concern as the finding is considered to be a variation of a normal anatomical feature. In most of the cases it means that the nerve impingement is not significant enough to cause pain.
What are the treatment options for trigeminal neuralgia?
The first choice of treatment is drug therapy. Pain treatment is usually started with carbamazepine or oxcarbazepine. If effective – most patients take these medications on a long-term basis, sometimes for years at a time. Some patients may take the medication intermittently during periods of exacerbation. However, if the disease progresses, patients have to take medications at higher doses, sometimes additional medications are prescribed which increases the risk of side effects, while all along the strain on vital organs such as the liver and kidneys continues to raise. Despite the fact that medications are capable of alleviating the pain, they cannot in any way solve the root of the problem – relieving the compression of the nerve by an adjacent blood vessel. If the patient does not opt for surgery, then the drug therapy can become lifelong.
Surgery is the treatment method of choice for those patients for whom drug therapy has failed and/or caused serious side effects or those who want to discontinue drug therapy.
The aim of surgery is to relieve the pressure excreted by the blood vessel on the nerve. Nowadays, thanks to the modern equipment available for surgery, it can be performed in a minimally disruptive and intrusive manner.. Surgery is done under general anesthesia. A small incision is made in the skin behind the ear on the affect side. A small fragment of the skull is removed by the surgeon to gain access to the operation field. The procedure is performed under a microscope, the blood vessel and the nerve are separated, a medical grade Teflon separator is inserted between them to ensure that the blood vessel remains separated after the surgery (see pictures below the text). The extracted bone fragment is usually reinserted at the end of surgery.
The effect of the surgery is immediately apparent upon waking up from anesthesia – the pain is gone. In most cases patient can be discharged home on next day after surgery. The effectiveness of surgery in patients with a classical presentation of a neurovascular conflict is very high – 90 to 95%. Patients may stop their drug therapy completely after the surgery. Patients remain pain free for years to come after the surgery.. Up to 72% do not experience any return of pain in a time period of 5-8 years.
In rare cases, when the trigeminal nerve pain is caused by another disease, such as multiple sclerosis, or surgery is not possible due to co-morbidities, other procedures such as rhizotomy may be used. The procedure encompasses the destruction of nerve fibers in order to alleviate pain. There are two ways to achieve rhizotomy – both are performed under the guidance of an X-ray: the nerve can undergo chemical lesion (with the use of special medications) or thermal lesion (using a heated probe). The lysed fibers no longer conduct signals and therefore alleviate the sensation of pain.. The effectiveness of this method is not as high as for stnadard surgery, it has a shorter duration of pain relief and can have unpleasant side effects (such as numbness of face). Rhizotomy is reserved for special cases, wherein other treatment methods have failed or are not feasible.
Typical trigeminal nerve pain is caused by direct contact between the nerve and the blood vessel, that is why neurosurgery is considered to be the “gold standard” (most effective) for treatment of this disease.