C. Nerve Injury/Destructive Procedures (Rhizotomies)
medications have failed to control TN, not all
sufferers are good candidates, or wish to undergo microvascular
decompression surgery. The alternative is destructive procedures that are
aimed to damage the trigeminal nerve (rhizotomy), usually at the Gasserion ganglion
or trigeminal nerve root. The resulting alteration
in nerve function usually leads to at least temporary alleviation of TN pain. However, the cause of TN, neurovascular compression
upon the nerve root, persists.
Prior to rhizotomy procedure.
Rhizotomy procedures are technically simpler than a microvascular decompression surgery, and can be repeated should the pain of TN recur. A general side effect associated with these procedures is numbness in the face. The numbness may be annoying (parasthesia) or even painful (dysesthesia). Rarely, patients develop an agonizing and permanent painful numbness or anesthesia dolorosa, which cannot be treated effectively by any medical or surgical means. Another serious but rare complication is loss of sensation to the cornea of the eye that may lead to keratitis and blindness. Loss of chewing strength on the treated side may occur, especially following balloon compression rhizotomies. Whenever destructive procedures are repeated, the incidence of these complications increases.
2. Types of Rhizotomies
a. Percutaneous Glycerol Rhizotomy
This is performed under local anesthetic. A needle (typically 3.5" x 20 G spinal needle) is inserted in the skin beside the mouth, and directed through an opening at the base of the skull (through the foramen ovale). A harmless dye may be injected to confirm the needle is in the precise location, as seen on an x-ray. The chemical glycerol is then injected into the space surrounding the Gasserion ganglion. This glycerol produces a relatively mild injury to the nerve with minimal risk of permanent facial numbness. While the majority of patients achieve early relief of TN pain with this technique, half of them will suffer a reoccurrence of pain within a few years. Repeat glycerol rhizotomy or other procedure may then be performed.
Glycerol is a clear viscous liquid chemical
X-ray imaging is used to direct the percutaneous needle to the Gasserion ganglion
b. Percutaneous Balloon Compression Rhizotomy
means to affect a percutaneous trigeminal rhizotomy is with a balloon compression
procedure. This is performed while the patient is under general anesthesia. The
needle advanced to the Gasserion ganglion is larger in caliber, and allows for
the passage of a special catheter fitted with an inflatable balloon. The balloon
is inflated to compress and mechanically injure the trigeminal nerve root and
Gasserion ganglion. This form of percutaneous rhizotomy is particularly effective
for pain involving the upper face (V1), as it has a small chance of causing
permanent loss of sensation to the cornea. However, many patients develop at
least temporary weakness of the chewing muscles following this balloon compression
procedure, and the degree of facial numbness is often more severe than with
a glycerol rhizotomy.
The introduced canula is positioned and balloon catheter advanced.
c. Radiofrequency Rhizotomy
Another method of percutaneous rhizotomy is referred to as radiofrequency rhizotomy. This procedure is performed with intravenous sedation, although patients must be awake enough through the procedure to describe the degree and extent of facial numbness produced by the radiofrequency lesion. The specialized electrode is advanced to the Gasserion ganglion, and its correct position tested with gentle electrical stimulation that produces tingling sensations in the face. The electrode is then heated to produce a thermal injury to the nerve, while the patient receives strong sedation. This form of percutaneous rhizotomy has the best long-term pain control, with about three-quartres of patients free of pain after five years. However, the long term success is dependent upon some degree of permanent facial numbness, and there is an associated risk of causing painful numbness or anesthesia dolorosa.
A specialized electrode is positioned in the Gasserion ganglion.
The electrode is heated with radiofrequency current causing thermal injury of the nerve.
d. Stereotactic Radiosurgery (Gamma Knife)
Recently, a new technique allows for focused radiation to be delivered to the trigeminal nerve root and produces injury and results similar to the other percutaneous rhizotomy procedures. Gamma Knife Radiosurgery is performed by applying a frame to the patient’s head and then obtaining a MRI. The patient is then positioned in the Gamma Knife, where up to 201 focused beams of cobalt radiation are directed at the trigeminal nerve root. This affects a delayed injury upon the trigeminal nerve and reduces TN pain within a few weeks in most patients. Higher doses of radiation may produce better pain control, but increase risks of developing facial numbness and other side effects. Details regarding the long-term effects and risks of this radiation treatment are still being studied.
e. Peripheral Trigeminal Nerve Blocks, Sectioning and Avulsions
Some TN sufferers have increased susceptibility to surgical complications involved in the procedures listed above. These include the very elderly, frail or medically infirm. A relatively simple means to injure the trigeminal nerve may be directed to trigeminal nerve branches exiting the skull, just under the skin or mouth lining. This portion of the nerve may be injured by injection of alcohol, cutting (sectioning) or avulsion of the nerve branch. While these techniques are usually effective immediately, they also cause severe or complete numbness of the affected area, at least temporarily. TN pain often recurs and therefore other surgical interventions are usually chosen for long-term disease control.
f. Microsurgical Rhizotomy
exposure and cutting of the trigeminal nerve root was introduced decades ago
and is an effective means to control TN pain, especially when the lower face
(V3) is involved. This operation, however, has been largely replaced with microvascular
decompression surgery and the percutaneous rhizotomy techniques. In rare situations,
microsurgical rhizotomy of the trigeminal root may still be performed. This
usually causes only partial loss of lower facial sensation (or numbness).
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M. Kaufmann & M. Patel
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