3.4  An Algorithm for the Surgical Treatment of Classical Trigeminal Neuralgia

By Margaret Tugend, BA, and Raymond F. Sekula, Jr., MD (USA)

In our clinic, we are working to better understand which patients with TN can benefit from surgical intervention. We know that patients with classical trigeminal neuralgia (TN1) fare better with most of the available surgical treatments than those with other types of TN. Information gleaned from a detailed history (i.e., a short conversation between patient and physician) allows the physician to make a diagnosis of TN1. Patients with TN1 describe sharp, intermittent facial pain usually lasting for seconds or less and never for longer than 2 minutes or so. This pain does not encompass the posterior third of the scalp or the ear. Triggers include innocuous stimuli such as light touch, wind, or chewing. Attacks may occur numerous times each day with periods (from days to months) of remission. Sensory deficit (i.e., orofacial numbness) is not a related symptom. Most patients with TN1 will wince (the so-called “tic douloureux” or painful spasm) with pain.

Figure 3-3. High-resolution MRI image demonstrating trigeminal nerve deformation (purple arrow) by the superior cerebellar artery (orange arrow).

All patients with TN1 will benefit from a neurosurgical consultation. Approximately 85% of patients with TN1 will have evidence of vascular compression of the trigeminal nerve by high-resolution T2-rated MRI images (which enhance the signal of water as opposed to fatty tissue). In our center, we perform high-resolution imaging (Figure 3-3) with a higher-power MRI magnet (i.e., T3 rating) than found in most community-hospital MRI machines.

Perhaps, more important than magnet strength is the “recipe” used to visualize the trigeminal nerve and adjacent vasculature. Too often, we review scans that do not allow a clinician to determine vascular compression of the trigeminal nerve. Why is this important? If a scan is interpreted as negative for vascular compression by a radiologist, the treating neurologist is led to believe that a referral to neurosurgery is unwarranted. We also know that the degree of vascular compression of the trigeminal nerve is important. Patients with more compression of the nerve do better with surgery. In some patients (as many as 15%) with TN1, there is no neurovascular compression. These patients do poorly with MVD. An analogy can be drawn to someone with tooth pain, but no structural problem of the tooth, who undergoes a root canal. The procedure just does not work and often worsens the pain. Those patients with TN1 without evidence of neurovascular conflict or an inability to tolerate a general anaesthetic may be best managed with a referral for an ablative procedure to the trigeminal nerve or ganglion or further medication management.

A patient’s response to the antiseizure drug carbamazepine or oxcarbazepine provides helpful information for the clinician. Many patients report rapid relief of facial pain within just minutes of the first tablet or two of these drugs. Although we do not fully understand why the response to these drugs is an important predictor of response to neurosurgical intervention, we do know that it is important. A few years ago, we and another group developed a readily applicable, quantitative grading or scoring system to aid patients and referring clinicians in understanding whether MVD is the optimal choice (Tables 3-1 and 3-2). Those with TN1 whose pain responds to medication and who have arterial contact or an arterial deformity have a higher probability of achieving long-term pain relief from an MVD. For others, an MVD has a much lower probability of success and might do more damage than good.

One of the unique challenges for individuals with TN1 is to avoid ablative procedures, if possible. Too often, neurologists and other clinicians relegate patients who are over the age of 65 years or in poor health to one of the ablative procedures rather than MVD. For a variety of reasons, this is a mistake. Although ablative procedures are useful in some circumstances, when patients have potentially fulfilling years ahead of them, these procedures are limited by a lack of durability (i.e., pain relief is short-lived) and increasing complications with repeat procedures. We and others have shown that individuals over 65 years of age and people with some medical conditions do as well as, or better than, others with a similar complication profile. Although the risk of stroke may be a bit higher for people over 65 years old, pooled data suggests that the risk of stroke is less than 1% in expert hands. Consult with doctors treating all of your medical conditions to see if you are healthy enough for an MVD. In expert hands, an MVD is the gold standard regardless of age and even considering some medical conditions.

Table 3-1. TN Scoring System
CHARACTERISTIC	POINTS ASSIGNED FOR CHARACTERISTIC
TN Symptom Type
Nonclassical	0
Classical (TN1)	1
Response to Medication
No	0
Yes	1
Neuro-vascular Contact
Absent or venous only	1
Arterial contact	2
Arterial deformity	3
Total TN System Possible Score	1 to 5

In summary, can the individual with TN1 expect from a well-performed MVD? If you consider the scoring system in Table 3-2, you will notice that the chance of long-term pain relief increases with an initial response to ox/carbamazepine and increasing degrees of vascular compression of the trigeminal nerve. Although some individuals with TN1 will experience a recurrence of trigeminal pain over time, the chance of pain recurrence is much lower with MVD than with any of the ablative procedures.

Table 3-2. Probability of Long-Term Relief (Without Medication) from MVD Using TN Score
TN Scoring System Score	Probability of Long-Term Pain-Free Status (%)
1	4
2	16
3	44
4	76
5	93