ハローベスト牽引固定により不安定性を証明し得た頭蓋底陥入症の1例

Efficacy of Halo-Vest Fixation in the Assessment and Prediction of the Effectiveness of Permanent Fixation in a Patient with Basilar Invagination with Ambiguous Vertebral Instability

Ⅰ．はじめに

　頭蓋底陥入症は大孔周囲構造が後頭蓋窩に陥入する機序により，直接の脳幹圧迫，もしくは脊髄空洞症を伴って症状が発現する．治療には前方圧迫要素である歯状突起の削除，併存するChiari奇形に対する大孔減圧術，不安定要素の解除を目的とした後頭骨・頚椎固定などが病態を考慮した上で選択されるが，どの要素が主たる病態なのかは確定困難であることも多く，疾患の稀少性も相まって病態診断から治療選択まで難渋することがある．今回われわれは若年男性の頭蓋底陥入症が，軽微外傷を機に脊髄空洞症の悪化を来して症状を発現し，苦慮しつつ診断・治療を行った症例を経験した．その病態診断・外科的治療に至る経緯について文献的考察を加え報告する．

　Basilar invagination is a developmental anomaly of the craniovertebral junction in which the odontoid abnormally prolapses into the foramen magnum. It is also associated with Chiari malformation, syringomyelia, and hydrocephalus. Patients require surgical treatment to prevent progression of neurological symptoms, but assessment of anterior or posterior decompression can be difficult owing to bone instability and ambiguous compression of neural structures. Here, we describe a case of basilar invagination in a young adult. He presented with neurological symptoms, including syringomyelia, 3 months after a traffic trauma that might have led to instability of the bony structures. Since it was unclear whether the instability of the bony structures contributed to the clinical deterioration, the patient was first treated using halo-vest fixation. Significant improvements were observed in both neurological symptoms and magnetic resonance images. These results justified the invasive fixation and the patient was treated further with an occipito-cervical fusion；good results were achieved in this case. Owing to the invasiveness of the procedure, occipito-cervical fixation should only be adopted following strict indication criteria. Halo-vest fixation was effective in treating the instability of the bony structures and as a trial treatment for permanent fixation.