Over the past several decades, stereotactic radiosurgery has become a viable noninvasive treatment option for patients with trigeminal neuralgia. The scientific literature regarding the radiosurgical treatment of trigeminal neuralgia has evolved to identify factors that predict both efficacy and toxicity. Radiosurgical management has, thus, become complementary to medical management, microvascular decompression, and percutaneous ablative procedures. Thus, effective management often requires multidisciplinary collaboration. The intent of this review is to discuss the role of radiosurgery in the modern management of trigeminal neuralgia and to review radiosurgical outcomes, targeting, and controversies.
Key points
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Stereotactic radiosurgery represents a safe and effective noninvasive treatment option for patients with trigeminal neuralgia.
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The major limitation of radiosurgery as compared with microvascular decompression is the limited durability of pain relief.
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Optimal populations for radiosurgery include patients older than 70 years, patients with multiple sclerosis, and patients with significant medical comorbidities.
Introduction
Trigeminal neuralgia, also known as tic douloureux , is a severe paroxysmal facial pain located within the trigeminal distribution on the face. This condition has been described as a “suicide disease” because of the severe intensity of the pain. Approximately 45 000 people in the United States have been diagnosed with trigeminal neuralgia.
Classification and Cause
Trigeminal neuralgia is one of several different types of facial pain that can have similar characteristics. The most widely accepted classification scheme for facial pain was published by Burchiel. The Burchiel classification is summarized in Table 1 . Classic idiopathic trigeminal neuralgia is known as type I trigeminal neuralgia in the Burchiel classification. It is defined as pain that is episodic at least 50% of the time. It is located within any of the 3 divisions of the trigeminal nerve. It is also commonly described as sharp, stabbing, or electrical shocklike in quality. The intensity of the pain has been described using the Barrow Neurologic Institute (BNI) pain scale. This scale is commonly used in the scientific literature to describe pain before and after an intervention and to compare results between multiple series. The BNI scale is summarized in Table 2 .
| Diagnosis | Clinical History |
|---|---|
| Type I trigeminal neuralgia | >50% episodic pain |
| Type II trigeminal neuralgia | <50% episodic pain |
| Trigeminal neuropathic pain | Caused by unintentional trauma (eg, tooth extraction) |
| Trigeminal deafferentation pain | Caused by intentional trauma (eg, rhizotomy) |
| Symptomatic trigeminal neuralgia | Multiple sclerosis |
| Postherpetic neuralgia | Herpes zoster outbreak in trigeminal distribution |
| Atypical facial pain | Somatoform pain |
| Pain Score | Definition |
|---|---|
| I | No trigeminal pain, no medication |
| II | Occasional pain, not requiring medication |
| III | Some pain, adequately controlled with medication |
| IV | Some pain, not adequately controlled with medication |
| V | Severe pain, no pain relief |
The pathophysiology of type I trigeminal neuralgia has been explained by what has become known as the vascular hypothesis . This hypothesis posits that the episodic pain syndrome of trigeminal neuralgia is caused by compression of the trigeminal nerve by a blood vessel. The most common offending vessel is the superior cerebellar artery. It is also thought that the brain settles within the cranial vault with age and, thus, creates a greater likelihood for such an interaction between blood vessel and trigeminal nerve in the more elderly population.
Other causes that can produce pain syndromes similar to idiopathic trigeminal neuralgia include multiple sclerosis, tumors of the skull base (eg, meningioma, acoustic neuroma, metastatic disease), Charcot-Marie-Tooth disease, Lyme disease, herpes zoster, traumatic nerve injury, and somatoform pain disorders. The importance of the various causes of facial pain with regard to the use of stereotactic radiosurgery (SRS) is the fact that radiosurgical management has a high rate of response for type I pain but an inferior response rate for some of the other causes. The risk of SRS-related toxicity, although low, is another reason to differentiate between the various causes of facial pain. Patients with herpetic neuralgia and neuropathic pain from traumatic nerve injury are unlikely to respond to radiosurgery.
Introduction
Trigeminal neuralgia, also known as tic douloureux , is a severe paroxysmal facial pain located within the trigeminal distribution on the face. This condition has been described as a “suicide disease” because of the severe intensity of the pain. Approximately 45 000 people in the United States have been diagnosed with trigeminal neuralgia.
Classification and Cause
Trigeminal neuralgia is one of several different types of facial pain that can have similar characteristics. The most widely accepted classification scheme for facial pain was published by Burchiel. The Burchiel classification is summarized in Table 1 . Classic idiopathic trigeminal neuralgia is known as type I trigeminal neuralgia in the Burchiel classification. It is defined as pain that is episodic at least 50% of the time. It is located within any of the 3 divisions of the trigeminal nerve. It is also commonly described as sharp, stabbing, or electrical shocklike in quality. The intensity of the pain has been described using the Barrow Neurologic Institute (BNI) pain scale. This scale is commonly used in the scientific literature to describe pain before and after an intervention and to compare results between multiple series. The BNI scale is summarized in Table 2 .
| Diagnosis | Clinical History |
|---|---|
| Type I trigeminal neuralgia | >50% episodic pain |
| Type II trigeminal neuralgia | <50% episodic pain |
| Trigeminal neuropathic pain | Caused by unintentional trauma (eg, tooth extraction) |
| Trigeminal deafferentation pain | Caused by intentional trauma (eg, rhizotomy) |
| Symptomatic trigeminal neuralgia | Multiple sclerosis |
| Postherpetic neuralgia | Herpes zoster outbreak in trigeminal distribution |
| Atypical facial pain | Somatoform pain |
| Pain Score | Definition |
|---|---|
| I | No trigeminal pain, no medication |
| II | Occasional pain, not requiring medication |
| III | Some pain, adequately controlled with medication |
| IV | Some pain, not adequately controlled with medication |
| V | Severe pain, no pain relief |
The pathophysiology of type I trigeminal neuralgia has been explained by what has become known as the vascular hypothesis . This hypothesis posits that the episodic pain syndrome of trigeminal neuralgia is caused by compression of the trigeminal nerve by a blood vessel. The most common offending vessel is the superior cerebellar artery. It is also thought that the brain settles within the cranial vault with age and, thus, creates a greater likelihood for such an interaction between blood vessel and trigeminal nerve in the more elderly population.
Other causes that can produce pain syndromes similar to idiopathic trigeminal neuralgia include multiple sclerosis, tumors of the skull base (eg, meningioma, acoustic neuroma, metastatic disease), Charcot-Marie-Tooth disease, Lyme disease, herpes zoster, traumatic nerve injury, and somatoform pain disorders. The importance of the various causes of facial pain with regard to the use of stereotactic radiosurgery (SRS) is the fact that radiosurgical management has a high rate of response for type I pain but an inferior response rate for some of the other causes. The risk of SRS-related toxicity, although low, is another reason to differentiate between the various causes of facial pain. Patients with herpetic neuralgia and neuropathic pain from traumatic nerve injury are unlikely to respond to radiosurgery.
Therapeutic options
Several treatment options have evolved over time, including the use of antiepileptic medications, microvascular decompression (MVD) surgery, percutaneous rhizotomy, and SRS. The treatment option used for each individual case depends on factors such as patients’ age, medical comorbidities, and prior treatment options that have either succeeded or failed. A proposed management algorithm is depicted in Fig. 1 .
Medical Management
The first-line therapeutic option for newly diagnosed trigeminal neuralgia is medical management. In general, antiepileptics are the most common type of medication used for trigeminal neuralgia, though tricyclic antidepressants, benzodiazepines, and narcotics have all been used. The single most effective medication for trigeminal neuralgia is carbamazepine (Tegretol). Other medications that have reported responses include phenytoin (Dilantin), baclofen (Gablofen), oxcarbazepine (Trileptal), gabapentin (Neurontin), and lamotrigine (Lamictal). Patients who have an initial response to medical management can undergo a trial of withdrawal of medications over time as the pain may undergo remission. It is not uncommon, however, for patients to become refractory to medical management over time, and these patients will commonly require surgical or ablative management. Furthermore, some of the antiepileptics will commonly have associated toxicities, such as sedation, cognitive changes, and ataxia. Carbamazepine, in particular, can have a high rate of such toxicities. Oxcarbazepine and gabapentin may have lower rates of toxicity. A common indication for surgical or radiosurgical intervention is when patients experience medication-related toxicity from antiepileptics that start to affect their quality of life.
MVD
MVD is a surgical technique involving a craniotomy and decompression of the trigeminal nerve from the offending blood vessel. Intraoperative insertion of an inert implant (generally Teflon, DuPont, Wilmington, DE) allows for the prevention of recurrent vascular compression. The chief advantage of MVD is the fact that the pain relief is durable and likely curative. In general, 70% of patients treated with MVD continue to be pain free 20 years after the operation. Operative morbidity and mortality is generally quite low but increases after 70 years of age, which is the age that noninvasive alternatives may have a greater therapeutic ratio.
SRS
SRS represents a noninvasive treatment option for trigeminal neuralgia, with its main advantage being its noninvasiveness and low morbidity rate. Most of the data that exist for radiosurgical management of trigeminal neuralgia is using the Gamma Knife (Elekta, Stockholm, Sweden), although there is an emerging literature for linear accelerator approaches. The major disadvantage of SRS is the limitation in the durability of the pain response. Most series have shown that the median duration of radiosurgical response to be on the order of 5 years. Although SRS can be repeated, for younger patients, even a second application of SRS may not remain effective throughout their lifespan. Elderly patients and those with surgical contraindications, such as severe cerebrovascular or cardiovascular disease or bleeding diatheses, may also be best treated with a radiosurgical approach.
Percutaneous Rhizotomy
Percutaneous ablative techniques have also shown success in the treatment of trigeminal neuralgia. These techniques include radiofrequency rhizotomy, glycerol rhizotomy, and balloon rhizotomy. The chief advantage of percutaneous ablative techniques is that pain relief is immediate and that they often do not require general anesthesia. Comparison of the percutaneous procedures has suggested that they likely have very similar response rates and durability of response. However, the likelihood of persistent hypesthesia may be higher than what is seen with MVD or a radiosurgical approach. The durability of response for percutaneous techniques is limited and similar to results with SRS.
Outcomes after trigeminal neuralgia radiosurgery
Because most of the data for radiosurgical outcomes have come using the Gamma Knife unit, for the purpose of this review, the following radiosurgical outcomes will refer specifically to Gamma Knife radiosurgery (GKRS) results, with the exception of the section specifically dedicated to linear accelerator approaches.
Prospective Studies
There are few prospective studies for the use of SRS in the treatment of trigeminal neuralgia. The first such study was a prospective study performed by a group from Marseille, France and was a quality-of-life assessment showing improvement in all quality-of-life parameters and finding that 58 of 83 (70%) responders were able to come off of medications. A second prospective study conducted at the Mayo Clinic looked at the cost-effectiveness of SRS versus MVD as a definitive treatment option for trigeminal neuralgia. In this study, MVD was more expensive in the near term; but for patients with longer life expectancies, it seemed to be the more cost-effective treatment option. The University of Pittsburgh conducted a randomized prospective study of 87 patients in which patients were randomized to 1 versus 2 isocenters. The rationale for such a study was to determine whether an increased length of nerve treated resulted in any difference in either efficacy or toxicity of radiosurgical treatment. Although there was no change detected in efficacy, the incidence of complications correlated with the nerve length irradiated (more facial numbness with 2 isocenters vs 1 isocenter).
Response Rate and Durability of Pain Response
Several large retrospective series have also been reported for trigeminal neuralgia after definitive SRS. The results of the largest series of GKRS for the treatment of trigeminal neuralgia are summarized in Table 3 . The series that have been reported have been shown quite similar results regarding pain response. In a series from Wake Forest, Marshall and colleagues reported a cohort of more than 400 patients with trigeminal neuralgia and reported an 86% initial response to pain within 3 months.
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