両側性三叉神経痛の1例—手術所見に基づく発生機序に関する考察

A Case of Bilateral Trigeminal Neuralgia and the Possible Onset Mechanisms Based on the Operative Findings

Ⅰ．はじめに

　特発性三叉神経痛は，三叉神経根のroot entry zone（REZ）近傍を走行する動脈あるいは静脈による圧迫で生じる場合が多く，その大半は片側性発症例であり，両側性三叉神経痛は0.6〜5%と稀である^2,21)．両側性三叉神経痛の特徴として，同時に発生する場合もあるが，その多くは一側発症後数カ月〜数年を経過して，反対側に時間差をもって発症することが多い^12,19,21)．また，両側性の場合は女性例が多く，静脈が責任血管として関与する場合が比較的多いとも報告されている^12,19,21)．しかしながら，三叉神経痛が両側性に発生する機序についての報告はほとんどないのが現状である．

　今回われわれは，三叉神経痛に対する神経血管減圧術（microvascular decompression：MVD）施行2年後に反対側に三叉神経痛を来し，再度MVDを施行した両側性症例を経験した．その手術所見に基づいて，両側性に三叉神経痛が発症する機序について考察したので報告する．

　Several cases of bilateral trigeminal neuralgia（TN）have been reported;however, the possible onset mechanism has rarely been discussed. We encountered a case of bilateral TN occurring in two stages. A 64-year-old woman presented with left TN. Magnetic resonance imaging showed the transverse pontine vein adhering to the left trigeminal root and superior cerebellar artery adhering to the right trigeminal root;however, no symptoms were noted. Immediately after microvascular decompression（MVD）on the left side, TN disappeared completely. However, 2 years postoperatively, the patient presented with right TN. The second MVD surgery revealed that the right cerebellar surface severely adhered to the dura mater, particularly under the surface of the tentorium. The arachnoid membrane at the cerebellopontine angle was slightly adhered. The patient was completely free from pain after the second MVD. The intraoperative findings suggested that the brain stem may have shifted and the cerebellopontine cistern may have narrowed because of cerebellar adhesion to the surrounding structures and arachnoid adhesion. We speculate that such structural changes in the posterior fossa after the first operation may have caused the asymptomatic vascular adhesion to change into the symptomatic offending adhesion over time.