Evaluation of Surgical Procedures for Trigeminal Neuralgia: POSTERIOR FOSSA SURGERY

In: Anesthesia

5 Nov 2009

Microvascular Decompression

MVD is based on the concept that compression of the trigeminal nerve causes trigeminal neuralgia (Tegretol drug is used for controlling certain types of epileptic seizures). This procedure purports to address the etiological basis of trigeminal neuralgia due to compression of the trigeminal nerve from blood vessels or tumors, which have resulted in demyelination of the nerve. There is evidence from clinical and anatomical studies that support the neurovascular compression theory of trigeminal neuralgia. MVD has been highly recommended by many neurosurgeons, as they think that it is the only technique that removes the cause of the pain and does not damage the trigeminal nerve. However, the fact that there are still patients who do not experience pain relief following MVD suggests that there may be other etiologies other than the compression of the nerve that could cause trigeminal neuralgia.

To date, many long-term series of patients who have undergone MVD have been reported. However, many series also include the evaluation of patients with other types of pain (eg, atypical neuralgia and tumors). This makes the comparison of results difficult. Barker et al have reported an excellent long-term (20 years) prospective longitudinal study on the outcome of MVD for trigeminal neuralgia in 1185 patients. Ten years after surgery, 70% of the patients had excellent final results; they were free of pain without need of medication. Major complications included deaths (0.2%), brain-stem infarction (0.1%), and ipsilateral hearing loss (1%). Initial relief of neuralgia pain was present in 98%. This is one of the best studies for MVD to date for trigeminal neuralgia (*Medication Tegretol is used for controlling certain types of seizures and relieving pain in patients with nerve pain in the face, jaw, tongue, or throat). The authors were skillful in the selection of patients, including only patients with primary trigeminal neuralgia. In addition, it was a blind study employing an independent observer to collect and analyze the results. Extensive appropriate statistical analysis was also used in this study. Fisher’s exact test, Mann-Whitney test, t test, and Kaplan-Meier analysis were used.

Partial Rhizotomy

The technique for rhizotomy using the posterior fossa approach is the same as that for MVD. The whole or part of the sensory division is sectioned, taking care to avoid the motor root. The results of partial rhizotomy are comparable with those of MVD. However, there is a trend for a higher recurrence rate following partial rhizotomy compared with MVD. Mortality and morbidity rates are similar as the surgery is approached through the similar posterior fossa. The major complication is sensory loss. Painful dysesthesia and anesthesia dolorosa are more likely after complete section and occur in about 8% of patients.
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Gamma-knife Radiosurgery

Gamma-knife radiosurgery is a new technique for the treatment of trigeminal neuralgia for which no long-term follow-up exists. A stereotactic head frame is screwed onto the skull, and stereotactic imaging is performed. The trigeminal system is irradiated. A maximum radiosurgical dose of 70 Gy or greater was associated with a greater chance of complete pain relief. Most patient series reported comprised of less than 100 patients with follow-up of less than 1 year. Kond-ziolka et al reported 80% initial pain relief in 106 patients who were followed for 18 months. Ten percent of the patients developed dysesthesia as a complication.

A recent gamma-knife radiosurgery study provides a longer-term follow-up period of up to 6.5 years. This study evaluated a large series of 220 patients with idiopathic trigeminal neuralgia who had been treated with gamma-knife radiosurgery and were followed for a median period of 2 years. This is an excellent study that selected a homogenous sample of patients with idiopathic trigeminal neuralgia and has the longest follow-up to date for radiosurgery. In addition, good statistical analysis and independent observers were used to collect the data. The median radiosurgery dose used was 80 Gy, with a range of 60-90 Gy. Complete or partial pain relief was obtained in 85.6% of patients at 1 year. At 5 years, 55.8% of patients still had complete or partial pain relief. Complete pain relief was achieved at a median time of 2 months, with most patients achieving this level of pain relief within 6 months. Interestingly, a further 10% of patients obtained complete pain relief at 6-33 months after the radiosurgery. The most important factor for poor response was the presence of atypical pain features in addition to the typical neuralgic pain. Only 10% of patients developed new or increased subjective facial paraesthesia or facial numbness.
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It is important to note that it may take a long time to achieve pain relief following radiosurgery. The median time to pain relief was 1 month, with a range of 1 day to 6.7 months. A wait for pain relief for 6.7 months is clinically impractical because trigeminal neuralgia patients need speedier pain relief. Although radiosurgery appears relatively benign and noninvasive, complications like cataract formation, tumor formation, or brain necrosis may occur after long-term follow-up. The low incidence of morbidity, particularly dysesthesia complications, is the greatest advantage of gamma-knife radiosurgery compared with all other surgeries used for the treatment of trigeminal neuralgia. The results for radiosurgery are not as good as those observed after MVD for typical trigeminal neuralgia, as noted in the Barker et al series of 1185 patients: complete pain relief was reported in 70% of patients at 10 years. However, ra diosurgery may be a good choice for patients with recurrent pain after MVD or percutaneous surgery has failed.

The Table compares the different surgical techniques used for the management of trigeminal neuralgia. All surgeries at the 3 levels could relieve the pain of *trigeminal neuralgia. However, peripheral surgery can be done in the office with little equipment and is suitable for medically compromised patients with low morbidity. The main disadvantage for peripheral surgeries is that the pain relief is relatively short (particularly for cryotherapy and alcohol injection), with recurrence within months. Surgery at the gasserian ganglion is associated with a lower recurrence rate of pain, but the morbidity is higher and the risk of dysesthesia is high, particularly for RT. MVD is associated with the lowest pain recurrence rate but has the highest morbidity and mortality rate.

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