Direct compression by megadolichobasilar anomaly as a cause of trigeminal neuralgia; a case diagnosed by MRI.

A 49 year-old man with trigeminal neuralgia caused by megadolichobasilar anomaly was described. The patient having neuralgic attacks in the second branch of the right trigeminal nerve for two and a half years showed the angiographic evidence of a tortuous and elongated vertebrobasilar artery and MRI of the brain clearly visualized the root entry zone of the nerve having been compressed by the main trunk of ectatic basilar artery. Cases of trigeminal neuralgia due to the compression by the basilar artery itself have been rarely described previously. In order to evaluate trigeminal neuralgia, MRI is essential to determine the relationship of the involved site of nerve to the pathogenic artery.