Ablative Procedures: Rhizotomies

What is rhizotomy?

Procedures that go through the cheek with a needle (percutaneous) are ablative- they work by damaging some of the fibers of the nerve that are ‘short-circuiting’. Ablative procedures are surgical, but are considered ‘minimally invasive’ treatments. Minimally invasive interventional pain therapies are possible options when drug therapy fails. In addition, for some people, MVD surgery is not suitable because of medical comorbidities or risk factors, and ablative procedures may be good alternatives. One advantage of rhizotomies is that the onset of pain relief can start within a day of the procedure. For people whose facial pain prevents them from eating, talking, or maintaining basic functions of everyday life, this quick action can make rhizotomy a good choice.

Balloon compression rhizotomy

Balloon compression for trigeminal neuralgia is a simple and effective outpatient treatment for trigeminal neuralgia. It is one of the ablative options that injures the trigeminal nerve in a very specific way.

Who is a candidate?

If you are not a good candidate for invasive surgical treatment and medication is not keeping your pain at a manageable level or is causing unacceptable side effects, a rhizotomy may be a good choice. If your pain consists predominantly of paresthesias, it is a consideration. Paresthesias are paroxysmal sensations that can be described as: jumping, flashing, shooting, pricking, boring, drilling, stabbing, sharp, cutting or lacerating. Balloon compression is especially indicated for those patients with stabbing pain in the region of the eyes. This is because the small fibers that do not have insulation mediate what is called the corneal reflex and thus their function is preserved. This is the reflex that protects your eye from scratches that can affect one’s vision over time.

How does balloon compression work?

A balloon is temporarily inserted through a needle placed through the cheek and is inflated under X-ray guidance. The balloon squeezes the trigeminal nerve root against the skull base for a selected time period at a measured pressure. The balloon only injures the insulation that individually surrounds thousands of ‘wires’ within the ‘cable’ that makes up the trigeminal nerve. By injuring this insulation, the ability of the nerve to conduct electricity is affected. It turns off the switch that allows the short-circuit upstream in the nerve to occur. It is this short circuit that leads to the electrical sensations a patient feels. Interestingly, these injured nerve fibers do not conduct pain sensation. They conduct the sensations of light touch that trigger the painful short circuit. Fibers in the nerve that conduct pain sensation are actually preserved.

Radiofrequency rhizotomy

Percutaneous stereotactic radiofrequency rhizotomy (PSR) produces a controlled injury to the trigeminal nerve and is therefore able to trade numbness for relief of TN pain. It does so by temperature-monitored heating of the trigeminal nerve fibers. The extent of numbness can vary, but in general, the amount of numbness is proportional to the duration of relief. Too much numbness can also be a problem because it can cause uncomfortable sensations.

PSR can limit numbness to a specific part of the face, especially if the pain originates in the lower face, jaw, or tongue. It is probably the only procedure that can reliably limit numbness to that part of the face. This is helpful because the more widespread the numbness, the harder it can be to tolerate. Numbness of the upper face that includes the surface of the eye creates the risk of eye irritation or even corneal scarring with loss of vision. Absolute control of the lesion is not possible, however, and sometimes one gets more numbness than planned despite the surgeon’s best efforts.

PSR can cause numbness in all three trigeminal divisions if necessary, but once the ophthalmic division is to be included, balloon compression offers at least some protection of the corneal reflex. For some reason, corneal reflex nerve fibers seem to be less vulnerable to the pressure of the balloon than to the heat of the radiofrequency electrode.

PSR procedure

Patients are briefly anesthetized with an intravenous medication. An entry point for the needle electrode is selected in the cheek an inch to the side of the corner of the mouth.

Trajectory guidance points can be marked on the face to help the surgeon set the proper angle of approach with the needle. The needle is passed to the floor of the skull to an opening where one of the three divisions of the trigeminal nerve enters the skull. The needle is then positioned in a dip in the skull base called Meckel’s cave. This is where the tip will lie among the nerve fibers of the trigeminal root and Gasserian ganglion (A ganglion is a swelling in the nerve that serves as a relay center for sensation on the face to the brain.).

The sharp inner needle used for insertion is then exchanged for a radiofrequency electrode. Patients are woken up to the point of “sleepy but effective communication.” Current is passed through the electrode to cause small shocks in the face, hopefully without triggering a TN attack. This allows the surgeon to maneuver the electrode to the correct location where stimulation is felt in the trigeminal division where the patient normally gets TN pains.

Once properly localized, the patient is again lightly anesthetized and the electrode’s radiofrequency current is turned up to the point that it causes the nerve fibers to heat up. At 50° centigrade, nerve conduction temporarily stops. At 60°, the proteins in the nerve fibers start to coagulate, and part of the nerve is injured. Between lesions, the patient is woken so that the location and degree of numbness can be tested until it is exactly what the surgeon wants for that specific patient.

Most patients are willing to exchange their TN pain for their mild new numbness. Over time, there is some diminishment of the numbness and some accommodation to it. Like putting on a new pair of shoes, the new sensation is stronger at first, but the brain starts to see it as the “new norm” over time. Recurrence of pain in spite of continued numbness is well known and one of the mysteries of the disease. It is presumed that this represents some intensification or progression of the disease, which must be within the nerve.

PSR can be repeated for recurrence, but each repeat procedure carries the need for more numbness and therefore the increased risk of troublesome numbness. PSR is one of the oldest and yet still one of the best procedures to relieve TN pain. It is an outpatient procedure with an acceptably low risk profile and can be an exceptionally good option for patients with medical reasons to avoid open surgery.

Glycerol rhizotomy

Glycerol injection is also an outpatient or overnight procedure. It is performed with intravenous sedation. A thin needle is introduced through a puncture in the cheek, next to the mouth and guided through a natural opening in the base of the skull. Just inside this opening is the trigeminal ganglion where all three nerves come together. A small amount of a substance called glycerol is injected into the nerve after your doctor identifies the fibers of the nerve using a special x-ray test. The glycerol bathes the ganglion. The glycerol inactivates the short-circuit of the pain fibers in the nerve.