Trigeminal neuralgia: an anatomically oriented review.

Trigeminal neuralgia (TGN) is a peculiarly painful paroxysmic disorder with an annual incidence of 4.3 per 100,000, which undergoes spontaneous remissions and recurrences. The pain, which is subserved by large not small fibers, can in some cases be triggered from outside the trigeminal territory and by other than mechanical stimuli. There are strong autonomic influences on the pain, and there is cutaneous vasoconstriction in the trigeminal territory in which it occurs. There are also sensory perception deficits for temperature in the affected region and for touch in the whole trigeminal territory. There is now increasing evidence that the majority of cases are caused by vascular compression of the fifth nerve at its point of entry into the pons, for the pain can be relieved (with restoration of the sensory deficit) by surgical decompression. No anatomical abnormalities of the (peripheral) trigeminal nerve have ever been satisfactorily demonstrated. Arguments are examined for the hypothesis that TGN is essentially a disorder of central processing, the term being taken to include the oligodendroglial-sheathed proximal segment of the nerve.