Trigeminal Neuralgia
Ronald Brisman, M.D.

Trigeminal Neuralgia: Radiosurgery Before Microvascular Decompression

Brisman R: Trigeminal Neuralgia: Radiosurgery Before Microvascular Decompression. World Neurosurgery (2012) 78, 1/2:69-70.   
The following is a revised personal version of the text of the final journal article.
In WORLD NEUROSURGERY (2012) 78, 1/2:149-154, Chen and colleagues compared microvascular decompression in 42 patients with trigeminal neuralgia whose pain recurred following an initial radiosurgery with 67 patients who underwent microvascular decompression without a prior radiosurgery (4). Intraoperative dissection was not significantly more difficult in one group or the other, and the overall recurrence rate was similar in the two groups although initial complete pain relief not requiring medicines was more likely (93 percent) in the radiated group versus 77 percent in the non-radiated group.  In those without prior radiation, sharp dissection was needed for thickened arachnoid in 7 of 67 (10.4 percent) patients while in previously radiated patients, sharp dissection was needed in 8 of 42 (19.0 percent) and another 4 (9.5 percent) patients had adhesions between the vessel and nerve that caused a significant increase in difficulty of dissection. There appeared to be a higher risk of new sensory deficits in the post-radiosurgery group although this did not reach statistical significance.

The above study shows that microvascular decompression can be done successfully with a good chance for pain relief and with a relatively small risk of complications whether or not patients have had a prior radiosurgery procedure. This supports the idea that many patients could have a minimally invasive procedure such as radiosurgery as an initial procedure. Should pain recur, they could have another procedure, which could still be minimally invasive such as a repeat radiosurgery or a needle rhizotomy or, if they choose, the more invasive microvascular decompression. If a minimally invasive procedure were chosen as the initial procedure, many patients would never need a microvascular decompression.

The advantage of microvascular decompression is that it probably has a greater chance of relieving pain without the need for medicines than do the lesser invasive procedures (2), and it is less likely to cause numbness, especially the bothersome kind. Nevertheless, microvascular decompression is not always accomplished without denervation, and the better results seen in the post radiated group (4), where there was also more post-operative denervation, suggests that pain relief in microvascular decompression is sometimes caused by denervation. Even though microvascular decompression can often be done safely, the risk of complications including severe problems are much greater than with less invasive procedures.

Another apparent advantage is that pain relief tends to occur immediately after microvascular decompression while it is usually delayed a few weeks following radiosurgery. However, full recovery from microvascular decompression often takes a few weeks, while patients undergoing radiosurgery can resume normal activities the next day. In addition, those patients undergoing microvascular decompression who have complications, such as cerebrospinal fluid leak, infection, meningitis, diplopia, cerebellar edema or hemorrhage or hearing loss may recover, but during the several weeks they take to recover, they have limitations that often prevent them from resuming fully their preoperative activities. As is the case for all neurosurgical procedures for trigeminal neuralgia, as well as microvascular decompression, not all patients are relieved and the chance of recurrence continues as long as patients are followed.

The study reported in World Neurosurgery (4) involves patients with typical trigeminal neuralgia that corresponds to Burchiel class 1 (TN1) and 2 (TN2) (3).  TN1 refers to those with spontaneous face pain where more than 50 percent of the pain is episodic and TN2 where more than 50 percent of the pain is constant as reported by the patient. While some patients with typical trigeminal neuralgia have constant pain that they report as being more than 50 percent of their pain, there are many patients with constant pain that is more than 50 percent of their pain who do not have typical trigeminal neuralgia. Patients with typical trigeminal neuralgia who have constant pain usually had typical paroxysmal, triggered pain before they developed constant pain; their constant pain is markedly improved when they hold completely still even for a few minutes; and their constant pain is (or was) relieved by carbamazepine or oxcarbazepine. These patients, when their pain is medically intractable, are good candidates for neurosurgical intervention as they are likely to respond well to either radiosurgery, needle rhizotomy or microvascular decompression.

Patients with atypical trigeminal neuralgia (often with constant pain that is not relieved by holding completely still or taking carbamazepine and may have been present from the very beginning of symptoms) respond less well to microvascular decompression (6), radiosurgery or needle rhizotomy than those with typical trigeminal neuralgia.

Several other factors have been associated with a worse chance of long-term pain relief following microvascular decompression: these include female gender, venous compression of the trigeminal root entry   zone, and duration of preoperative symptoms exceeding 8 years (1). The study in World Neurosurgery (4) shows very good results in patients with a previous Gamma Knife radiosurgery even though they had a long duration of preoperative symptoms (median of 8 years). This would further argue against the need for an early microvascular decompression.
Most of the radiosurgical literature for trigeminal neuralgia involves Gamma Knife radiosurgery although there are some studies showing that Linac systems can also deliver safe and effective treatment for trigeminal neuralgia. Initially it was shown that pain relief was more likely when at least 70 Gray maximum was given to the cisternal trigeminal nerve (5). Most centers using Gamma Knife radiosurgery now deliver maximum doses between 75 to 85 Gray. An additional factor that will affect pain relief as well as complications is the proximity of the radiation to the dorsal root entry zone of the brainstem, as a smaller dose delivered here is probably as effective as a larger dose delivered further away from the brainstem. Special care must be taken especially when there is a small trigeminal cistern, which usually occurs in younger patients who have less brainstem atrophy. It is relatively easy under these circumstances to give a higher dose to the brainstem than otherwise anticipated and to risk major trigeminal denervation; it may be better to either decrease the maximum dose, or move the isocenter further away from the brainstem.

There is no simple formula for the best treatment that fits all patients with trigeminal neuralgia. Although microvascular decompression is an excellent procedure, the minimally invasive techniques of needle rhizotomy and radiosurgery present a very attractive alternative, especially as an initial procedure.
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