It has become apparent that a proportion of ostensibly idiopathic cases are caused by compression of the trigeminal roots by a small tortuous branch of the basilar artery. This was originally pointed out by Dandy and brought to greater attention by Jannetta, who has observed it frequently and has devised a procedure that is now widely used to relieve the pain by decompression of the trigeminal root. The offending small vessel is removed from contact with the proximal portion of the nerve (see below). The tortuous vessel can often be visualized by special MRI sequences or by MR angiography but these vessels can be found asymptomatic patients as well. This and other disorders of the fifth nerve, some of which give rise to facial pain, are discussed in Chap. 44.
Carbamazepine is effective in 70 to 80 percent of patients (600 to 1,200 mg/d), but half become tolerant over a period of several years. Other antiepileptic drugs such as phenytoin (300 to 400 mg/d), valproic acid (800 to 1,200 mg/d), clonazepam (2 to 6 mg/d), gabapentin (300 to 900 mg/d or more), pregabalin (150 to 300 mg/d), and carbamazepine in combination with other medications, suppress or shorten the duration and severity of the attacks in most patients for varying times. Baclofen may be useful in patients who cannot tolerate carbamazepine or gabapentin, but it is most effective as an adjunct to one of the anticonvulsant drugs. Capsaicin applied locally to the trigger zones or the topical instillation in the eye of an anesthetic has been helpful in some patients. By temporizing and using these drugs, one may permit a spontaneous remission to occur in perhaps 1 in 5 patients over a year or two.
Many patients with intractable pain, however, come to vascular surgery or a surgical form of root destruction. The vascular decompression procedure, which requires a posterior fossa craniotomy but leaves no sensory loss, has been the most consistent approach. Barker and colleagues reported that 70 percent of 1,185 patients were relieved of pain by repositioning a small branch of the basilar artery that was found to compress the fifth nerve, and this benefit persisted with a recurrence rate of less than 1 percent annually for 10 years. The procedure has been done sometimes without confirmation of a vascular loop by vascular imaging.
A procedure employed more in the past but still finds use, was stereotactically controlled thermocoagulation of the trigeminal roots (Sweet and Wepsic). In recent years, there has been a preference for microvascular decompression on the basis of its sparing of sensation, especially late in the course of the illness (Fields). Several forms of stereotactic radiation are less intrusive alternatives, but their full effect is not evident for months. In practice, an antiepileptic medication is often required for some period of time after any of these procedures, and it must be reinstituted when symptoms reoccur, as they often do.
This syndrome is much less common than trigeminal neuralgia but resembles the latter in many respects. The pain is intense and paroxysmal; it originates in the throat, approximately in the tonsillar fossa, and is provoked most commonly by swallowing but also by talking, chewing, yawning, laughing, etc. The pain may be localized in the ear or radiate from the throat to the ear, implicating the auricular branch of the vagus nerve. For this reason, White and Sweet suggested the term vagoglossopharyngeal neuralgia. This is the main craniofacial neuralgia that may be accompanied by bradycardia and even by syncope, presumably because of the triggering of cardioinhibitory reflexes by afferent vagal pain impulses. There is no demonstrable sensory or motor deficit.