2.9 Bilateral Facial Pain
By Jeffrey A. Brown, MD, FACS, FAANS (USA)
Is it real? Yes, it is—rare but real. Bilateral comes from Latin bi meaning two, and lateral meaning side or flank. Bilateral facial pain refers to pain on both sides of the face. It can occur concurrently, meaning that both sides hurt at the same time, or sequentially, meaning that there is pain on one side and then on the other. Bilateral facial pain more often occurs in people who have multiple sclerosis (MS), Chiari malformations, and a few other rare conditions.
We begin by examining why people with MS can experience bilateral facial pain. The brain consists of a mixture of gray matter and white matter. Ganglia are clusters of nerve cells found throughout the body. They carry nerve signals to and from the central nervous system (CNS). Large congregations of ganglia are in so-called gray matter. White matter is found in the deepest brain tissues. It connects the different parts of the brain. A straightforward way to visualize this is to think of the brain as a computer. The gray matter is the hardware. White matter represents the cables that connect the network and transmit signals. MS is a disease of white matter in the brain and spinal cord. Most nerves are not “naked.” They are covered in a fatty substance called myelin that improves their ability to conduct impulses rapidly. The white appearance of myelin gives white matter its name. In MS, the sclerotic plaques that form are in the white matter and disturb its function. Because the trigeminal nerve has a high concentration of white matter and the face is extremely sensitive to touch, the trigeminal nervous system is prone to injury in MS patients. It is not limited to one side of the body.
Why do these sclerotic plaques cause pain? They injure the myelin, so nerves can be naked. When electricity surges through them, there can be short circuits that we feel as stabbing or sometimes continuous electrical, burning pains.
Because there is primary injury to the nerve, the TNP of MS is hard to treat. It is unlike TNP resulting from a vascular contact or distortion of the trigeminal nerve. These vascular abnormalities can be dealt with primarily by decompressing the nerve, that is, moving the offending artery or vein and placing a tiny pillow between the nerve and artery or vein to avoid further contact. That is usually not possible in people with MS. Sometimes, however, people with MS can have TNP for a reason unrelated to their MS and can be treated by decompressing the nerve. This is especially true if the MS has been inactive for many years before the onset of TNP.
Are there other ways for pain to be bilateral? Yes. Some young people with Chiari malformations may be more prone to bilateral facial pain. The Chiari malformation is a consequence of a temporary developmental arrest in utero of the early developing hind portion of the skull. This is the back of the skull that contains the cerebellum, which is the balance control portion of the brain. During the brief period when the skull is not growing, the brain is still growing. When the skull growth starts up again, the hindbrain does not fit into its package, and space is tight, sometimes tight enough that the hindbrain slips down into the spinal canal to find room. You can understand that, in this situation, arteries and veins in tight quarters are more likely to be forced up against the trigeminal nerve, which enters the brain stem in this region of the skull, called the posterior or back fossa or cave. Individuals with this experience in utero may be more prone to developing trigeminal neuralgia and having bilateral TNP. They may even have a combination of trigeminal and vagoglossopharyngeal neuropathic pain, as both areas would be subject to the complications of tight quarters.
Does anyone else experience bilateral facial pain? There is another group of people who have pain, but not with a compressive cause. They may have an immunologic cause of their pain such as scleroderma, lupus, or Sjögren’s syndrome. (See the next article by Hossein Ansari, MD, on medical causes of facial pain.) These conditions can be diagnosed by laboratory studies and may be associated with other signs separate from the facial nerves, such as perennially cold hands, dry mouth, tight skin, or a butterfly rash on the face.
What about burning mouth syndrome? Because this syndrome is of unknown cause and unclear treatment, it should not be a diagnosis delivered lightly. Patients with venous contact on the trigeminal nerve are more likely to have continuous burning pain than those with arterial contact. If the pain is bilateral, vascular contact should be investigated before a diagnosis of burning mouth syndrome is issued. To make such a diagnosis, one has to undergo an MRI scan done with certain software adjustments that have the acronyms FIESTA, CISS, or VIBE. These techniques allow one to distinguish between spinal fluid, arteries, veins, and nerves. The MRI scan is done with thin cuts that provide the best possibility of seeing such vascular contact when the images are viewed in three different planes (axial, sagittal, and coronal) simultaneously. (See Figures 2-5 and 2-6.)
Figure 2-5. MRI image in the coronal (straight-ahead) view showing the right trigeminal nerve (lower arrow) in contact with an artery (upper arrow) in a patient with bilateral facial pain.
Figure 2-6. MRI image in the coronal (straight-ahead) view showing the left trigeminal nerve (left arrow) in the same patient in contact with loops of an artery (right arrow).
What happens when the diagnosis of bilateral TNP secondary to compressive neuropathy is made, and medication no longer provides relief? If surgery is needed, it should be done on the most painful side first. Surgery on the other side should be delayed for several months to allow time for recovery from the first operation. Bilateral injury to the brain from surgery in a single session is to be avoided, as it can inflict a devastating injury should it occur.
In summary, bilateral vascular compressive TNP is an unusual condition of an already unusual condition, so the diagnosis is best obtained from a physician well experienced in the treatment of TNP.
