Unusual Nerve-Artery Relationship in Microvascular Exploration for Tic Douloureux

To the Editor: The patient, a white woman, developed tic douloureux involving the right first and second divisions at the age of 48 years. She was treated conservatively with carbamazepine (Tegretol; Novartis Pharmaceutical Corp., East Hanover, NJ), but after 2 years, her pain had become increasingly difficult to control with an adequate dosage of Tegretol; thus, surgical intervention was recommended. After discussing the pros and cons of microvascular decompression versus percutaneous thermocoagulation, she elected to undergo decompression. At surgery, the anteroinferior cerebellar artery initially seemed to be compressing the superior aspect of the trigeminal nerve. However, careful dissection of arachnoid tissue around the artery-nerve complex revealed that the artery was, in fact, penetrating the midportion of the nerve approximately 5 mm distal to the brainstem (Fig. C4). After penetration, the artery disappeared ventrally and caudally. The portio minor of the nerve was not involved.FIGURE C4.: Drawing showing the anteroinferior cerebellar artery (AICA)-nerve complex.Preoperative magnetic resonance imaging suggested that the anteroinferior cerebellar artery was adjacent to the nerve. At surgery, dissection was not extended farther than required for the procedure; thus, the anteroinferior cerebellar artery could not be confirmed with certainty. It is possible that the artery was the superior cerebellar artery, although a persistent abnormal pontine artery could be considered (1, 2). Because the pain involved the first division, resection of the upper portion of the nerve was thought inadvisable and there was concern that sectioning the lower portion of the nerve would fail to relieve the pain. Resection of the artery was not considered. Therefore, with the use of careful blunt dissection, the upper and lower halves of the trigeminal nerve were carefully separated distal to the artery, allowing for a large opening for the artery and precluding compression of the nerve. This enlargement allowed the artery to be freely movable in its passage through the nerve. Nothing further was done. After surgery, the patient was pain-free. Within 6 months, some pain in the right first division was occasionally felt. This slowly worsened, again, with inadequate control by Tegretol. Therefore, 2 years after her decompressive procedure, percutaneous thermocoagulation of the first division of the right trigeminal nerve was carried out with relief of the recurrent pain. Subsequently, she developed some occasional flicks of pain along with some return of pinprick pain perception in the right first division. However, the corneal reflex remains absent, and she has some continuing problems of dryness of the cornea and conjunctiva in the right eye requiring ophthalmological follow-up and the use of artificial tears. The mild pain is controlled with gabapentin (Neurontin; Pfizer, New York, NY). Bernard S.