Trigeminal neuralgia is characterized by severe, episodic pain in the trigeminal nerve distribution. Medical therapy is the first line treatment. For patients with refractory pain, a variety of procedures including microvascular decompression, percutaneous radiofrequency rhizotomy, percutaneous glycerol rhizotomy, percutaneous balloon compression, and stereotactic radiosurgery are available. We review the literature and suggest that microvascular decompression remains the gold standard operative therapy. For patients with recurrent pain or who are poor operative candidates, percutaneous radiofrequency rhizotomy offers the best pain response rates and has the advantage of being able to selectively target affected trigeminal divisions.
Key points
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Microvascular decompression offers superior long-term pain outcomes for patients with type I trigeminal neuralgia; however, it is associated with the highest rate of serious complications.
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For patients with recurrent pain after microvascular decompression or who are poor operative candidates, percutaneous radiofrequency rhizotomy is the best option among the percutaneous procedures.
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Percutaneous radiofrequency rhizotomy offers the best initial and long-term pain response rates and has the advantage of being able to selectively target affected trigeminal divisions.
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Stereotactic radiosurgery may be useful in patients who fail multiple operative procedures or who have multiple sclerosis–associated trigeminal neuralgia.
Introduction
Trigeminal neuralgia (TN) is characterized by severe, episodic pain in the distribution of the trigeminal nerve. Type I TN is characterized by episodic lancinating pain, and type II TN has a constant pain component. A variety of methods are used to measure pain severity in TN, with one of the most common being the Barrow Neurologic Institute (BNI) pain scale, which ranges from a score of I indicating no pain and not taking any medications to V indicating severe pain with no relief. Although pharmacologic treatment with medications such as carbamazepine is the first-line therapy, for patients who have resistant pain or who cannot tolerate medications owing to adverse effects a number of operative interventions are available. These include microvascular decompression (MVD), percutaneous radiofrequency rhizotomy (PRR), percutaneous glycerol rhizotomy (PGR), percutaneous balloon compression (PBC), and stereotactic radiosurgery (SRS), including gamma knife radiosurgery (GKRS) or cyberknife. These procedures have varying success rates and risk profiles. We review the evidence supporting the risks and benefits of the various operative modalities.
Introduction
Trigeminal neuralgia (TN) is characterized by severe, episodic pain in the distribution of the trigeminal nerve. Type I TN is characterized by episodic lancinating pain, and type II TN has a constant pain component. A variety of methods are used to measure pain severity in TN, with one of the most common being the Barrow Neurologic Institute (BNI) pain scale, which ranges from a score of I indicating no pain and not taking any medications to V indicating severe pain with no relief. Although pharmacologic treatment with medications such as carbamazepine is the first-line therapy, for patients who have resistant pain or who cannot tolerate medications owing to adverse effects a number of operative interventions are available. These include microvascular decompression (MVD), percutaneous radiofrequency rhizotomy (PRR), percutaneous glycerol rhizotomy (PGR), percutaneous balloon compression (PBC), and stereotactic radiosurgery (SRS), including gamma knife radiosurgery (GKRS) or cyberknife. These procedures have varying success rates and risk profiles. We review the evidence supporting the risks and benefits of the various operative modalities.
Microvascular decompression
Success Rates
MVD involves performing a suboccipital craniotomy to find and resolve the underlying trigeminal nerve compression ( Fig. 1 ). MVD offers excellent pain control results. The rate of initial pain control is 80.3% to 96%. One prospective study found that 92.5% of patients were pain free without medication at average 28 month follow-up. In another study at mean of 38 months of follow-up, 85% of patients maintained adequate pain control. At 5 years, 72% to 85% have good pain control. One of the largest studies of MVD with long-term follow-up found that at 10 years 70% of patients had complete pain relief and 4% had partial pain relief. Another study with very long-term follow-up found that at 15 years 73.4% of patients were pain free. Pain relief after MVD is generally instantaneous, although a delay of up to 1 month before the benefit is evident has been reported.
MVD has highest success rates in patients with type I TN. Type II TN may have more advanced underlying nerve damage contributing to worse immediate and long-term outcomes. Arterial versus venous compression may also be associated with TN type and is associated with better outcomes after MVD. In patients with episodic pain that evolves into constant pain, MVD may still provide significant pain relief, especially for the episodic component of pain. However, freedom from pain is less likely if constant pain comprises more than 50% of the pain experienced.
A greater degree of neurovascular compression has been associated with better long-term outcomes in some studies, as has the presence of preoperative trigger points. Patients with immediate postoperative pain relief, male gender, absence of venous compression, and shorter disease duration may have better outcomes. Bilateral pain is correlated with worse outcomes. MVD is less effective for multiple sclerosis (MS)-related TN, with 50% experiencing complete pain relief and 10% partial pain relief at a mean of 2 years of follow-up.
Because MVD is more invasive than other surgical procedures for TN, its safety and efficacy in older patients has been debated. One study suggested that although all ages had the same rate of initial pain relief (>95%), patients over age 60 had a shorter time to recurrence. However, the older patient group had a longer duration of symptoms before surgery, which may have contributed to worse outcomes. Another study found lower recurrence rates in elderly patients. Older patients may have better outcomes after repeat MVD. Young patients may have worse outcomes after MVD, perhaps related to a lower incidence of arterial compression at the time of surgery.
MVD can be successful as a repeat procedure for appropriately selected candidates who have recurrence of TN after initial MVD or other surgical procedure, although rates of pain relief are likely lower than with initial MVD, with 90.3% to 93.3% initial complete pain relief, 67% success rate at 12 months, and 42% excellent results at 10 years. Another study that included partial sensory rhizotomy in repeat MVD found 10% good outcome at the 4-year follow-up. Patients with previous ablative procedures have worse outcomes after MVD, with 64% reported excellent outcome at a mean of 5.1 years of follow-up.
Complications
Although MVD is the most invasive operative procedure for TN, in experienced hands the complication rate is relatively low. There is a 4% rate of serious complications. Mortality rate is reported at 0.15% to 0.8%. There is a lower complication rate and lower rate of mortality or discharge to other than home with greater hospital and surgeon volume.
MVD has a 1.6% to 22% rate of postoperative trigeminal nerve deficit, with approximately one-half of cases being transient. Facial weakness occurs in 0.6% to 10.6%, with some deficits improving with time. There is a 1.2% to 6.8% rate of hearing loss. Monitoring brainstem evoked responses during the procedure may help to decrease this complication, which is often associated with retraction. Two percent experience aseptic meningitis. Hydrocephalus occurs in 0.15%. The reported rate of cerebrospinal fluid (CSF) leak is 1.5% to 4%. Cerebellar infarct or hematoma may occur in 0.075% to 0.68%. Anesthesia dolorosa is reported at rates from 0% in one large series to 4% in patients who underwent internal neurolysis during MVD.
Two studies using the Nationwide Inpatient Sample found a relationship between mortality and discharge to other than home and age. Age also correlates with incidence of cardiac, pulmonary, thromboembolic, and cerebrovascular complications but not with CNS infection, wound complications, cranial nerve deficits, or CSF leak. Other studies including a meta analysis of studies examining MVD and age have reported no difference in complication rates.
Patients with prior MVD may have a higher complication rate. Trigeminal nerve complications may be higher and have been reported at 8.3% to 32% after repeat MVD. Hearing loss occurs in 6.7%.
Percutaneous treatments
Percutaneous Radiofrequency Rhizotomy
Success rates
Percutaneous procedures use a needle to access the gasserian ganglion and introduce injury via heat, chemical injury, or mechanical compression ( Fig. 2 ). Reported outcomes after percutaneous procedures are more variable, depending in part on the outcome measure used. Initial response rate to PRR is reported at 97.6% to 99%. At 6 months, there is a 83.3% to 89.9% response rate. Reports of recurrence rates vary from 38.2% at 1 year to 10% at 6.5 years follow-up. A large series reported 41% of patients retaining complete pain control after 20 years.
Type I TN is associated with better outcomes after PRR, although bilateral pain and comorbid psychiatric conditions may be associated with worse outcomes. An advantage of PRR is that it may allow more selective targeting of trigeminal nerve distributions than other percutaneous procedures. PRR is effective for MS-related TN, but requires the production of anesthesia in the affected trigeminal divisions.
Complications
Hypesthesia lasting at least 1 month occurs in 3.3%. There is a 5.7% to 17.3% rate of decreased corneal sensation with an 0.6% to 1.9% rate of keratitis. Four percent of patients experience masseter weakness. There is a 0.6% to 0.8% rate of anesthesia dolorosa. PRR damages small unmyelinated pain fibers contributing to adverse effects. Higher temperatures may be associated with the rate of hypesthesia.
Percutaneous Glycerol Rhizotomy
Success rates
Seventy-one percent to 97.9% of patients have immediate and complete pain relief. PGR has mean duration 11 months. At 1 year to 13.5 months of follow-up, there is a 53% to 63% rate of pain control. At 54 months, the recurrence rate is 72%. At 5 years, 56.5% recur. Another study reported a 10-year recurrence rate at 18.8%, with most recurrences occurring within the first 3 years.
High preoperative pain score, postoperative hypoesthesia, and presence of pain-free intervals are correlated with outcome after PGR. CSF outflow during the procedure is correlated with lower recurrence rates. Three or more prior PGRs are correlated with shorter time to recurrence.
There are reports of similar and worse outcomes for type II TN after PGR, with 100% experiencing recurrence within 1 year. PGR may relieve the episodic but not constant pain component in type II TN.
MS-related TN may have a higher recurrence rate, with 78% recurring within a mean of 13 months. Another study found 78% initial complete pain relief with 59% recurrence at a mean of 17 months. Outcomes were better in patients with hypesthesia.
Complications
Aseptic meningitis occurs in 0.12% to 3% of patients and bacterial meningitis in 1.5% to 1.7%. Carotid puncture occurs in 0.77%. Penetration of buccal mucosa occurs at a rate of 1.5%, and cheek hematoma in 7%. Hypesthesia occurs in 23.3% to 72%, with higher rates in patients undergoing repeat procedures. Decreased corneal sensation occurs in 6.3% to 15%. There is a 1.9% rate of hearing loss.
Percutaneous Balloon Compression
Success
There is a 82% to 93.8% initial response rate. At 1 year, there is a 25.4% recurrence rate. At a mean of 4 years, long-term pain control is 69.4%. Another study found a 20% recurrence rate at 5 years. At a mean of 10.7 years of follow-up, there is a 31.9% recurrence rate. Time to symptom recurrence may be related to balloon compression time and to duration and extent of hypesthesia.
Repeat PBC for recurrent TN may be effective with 83% to 93.8% of patients having immediate pain relief. At a median of 64.8 months of follow-up, 54.5% remained free of pain.
Complications
PBC has a high rate of hypesthesia, with 89% to 100% of patients having initial numbness and 4.6% to 40% having some persistent symptoms. Trigeminal nerve dysfunction may be proportional to the rate and duration of balloon compression. There is a 0% to 3.1% rate of decreased corneal sensation. PBC selectively injures medium and large myelinated pain fibers, preserving small myelinated and unmyelinated fibers, which help to preserve corneal sensation.
Hearing loss occurs in 2.4% to 6.3%, whereas 1.2% to 12% experience masseter weakness. Cheek hematoma occurs in 3.5% to 6.7%. Aseptic meningitis is reported in 0.7% and bacterial meningitis in 0.7% to 1%. Pseudoaneurysm may occur in 1%. PBC may have a higher rate of trigeminal reflex bradycardia and hypotension than other percutaneous procedures, potentially making it less suitable for patients with underlying cardiac comorbidities.
Patients undergoing repeat PBC may have a higher rate of jaw weakness and decreased corneal sensation. There is a high rate of trigeminal nerve dysfunction, with 55% experiencing persistent numbness. One study of PBC after previous other failed procedure found a 7% rate of ipsilateral facial weakness and 0% to 3.4% of anesthesia dolorosa.
Stereotactic Radiosurgery
Success rates
After GKRS 79% to 91.8% of patients have initial pain improvement. Pain improvement after GKRS is delayed, with 10 days to 3.4 months weeks until pain relief. Duration of symptoms is associated with latency of response. Earlier response may be associated with durability of response. Median duration of pain relief is reported at 32 months to 4.1 years. At 1 year, 75% to 90% have BNI I to IIIB pain scores. At 3 years, 70% maintain improvement in pain, with 34% pain free without medication. At 5 to 5.6 years, 44% to 65% of patients retain pain relief. Another study reported 76% are pain free at 7 years. At 10 years, 30% to 51.5% maintain good pain relief. In a large cohort of TN patients who underwent GKRS, 29% ultimately required further procedures for pain control.
Patients who have not previously undergone surgery have more durable pain relief. Initial medication responsiveness is also a positive predictor of outcome. Some studies report no difference in response rates between different radiation doses. With a constant radiation dose, the dose rate may be associated with pain relief outcomes after GKRS. Older age may also be associated with better outcomes, as is shorter duration of symptoms. Postprocedure facial numbness is associated with pain outcomes. Although neurovascular compression does not predict response to GKRS, dose to site of compression and distance from isocenter to site of compression are associated with pain relief. Type I TN patients are more likely to have initial response and less likely to relapse after GKRS. In bilateral TN GKRS has 80% pain control rate at 12 months and 65% at 36 months.
Repeat GKRS may be effective in patients who have recurrence after initial GKRS, with 60% to 100% with initial pain response after repeat procedure, with 75% maintaining pain freedom at 1 year and a median duration of response of 3.8 years. Patients who have a good response to initial GKS have better response to repeat procedure, as do those with hypesthesia after initial procedure. Radiation dose may be correlated with response to repeat GKRS. In patients undergoing a third GKRS procedure, 47.1% had initial BNI I scores and 47.1% BI II to IIIb scores at a mean of 2.9 months after the procedure, with 35.3% maintaining BNI I and 41.2% BNI II to IIIb scores at a mean of 22.9 months of follow-up.
Patients who underwent GKRS after failing previous surgical treatment for TN had 81% BNI I to IIIb rates of pain control at 1 year. In another study, patients undergoing GKRS for recurrent pain after initial MVD, GKRS, or PRR found 66% with a BNI score of I to IIIb at a median of 3 years of follow-up. At 6 years, there is a 58% rate of BNI I to IIIb pain control. Hypesthesia is associated with better outcomes, as is fewer previous interventions. In patients who had previously undergone MVD, 77.8% achieved initial pain freedom after median 14 days, significantly faster than in the general TN population. At 10 years, 44.3% remained pain free without medication.
After cyberknife radiosurgery, 61.9% to 87.2% of patients have initial pain relief. There is a 19-month median time to pain recurrence. At a median of 24 to 28 months of follow-up, 72% of patients have good pain outcomes. At 2 years of follow-up, 72% of patients had good pain outcomes. Hypesthesia is associated with better outcome. A higher initial pain score may be associated with better pain outcomes.
Complications
There is a 6% to 42% rate of hypesthesia after GKRS, with similar rates after cyberknife radiosurgery. Hypesthesia may be delayed, occurring at a median of 12 months. Hypesthesia is dose dependent and may be related to the proximity of the target to the brainstem. Anesthesia dolorosa has been reported in 0.2%.
After repeat GKRS, there is a higher rate of hypesthesia at 11% to 80% and a 6.6% rate of corneal dryness. A cumulative radiation dose of more than 115 Gy may be related to hypesthesia. A reported 1.3% of patients experienced anesthesia dolorosa.
When GKRS is performed after initial failed MVD, GKRS, or PRR, there is a 9.3% to 26% rate of new facial numbness, which is associated with radiation dose. Anesthesia dolorosa occurs in 0.5%.
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