環椎後弓欠損の２例

Abstract

Partial or complete aplasia of the posterior arch of the atlas is a rare anomaly. The purpose of this paper is to illustrate radiological findings and review literature on congenital defects of the posterior arch of the atlas. Case 1 : A 20-year-old woman diagnosed with abnormality of the posterior arch of the atlas was referred for further diagnostic follow-up in this hospital. She complained of nonspecific neck pain and headache, but neurological examination results were normal. Roentgenograms and CT scans revealed absence of the posterior arch of the atlas except for the posterior tubercle. Case 2 : A 20-year-old woman underwent medical check-up for cubital pain and numbness. Routine lateral view of cervical X-rays showed abnormality of the posterior arch of the atlas. There was partial defect of posterior arch of the atlas in 3D-CT. The posterior arch of the atlas became gradually thin in the axial view of CT. As a result, the posterior atlantodens interval remained wide. The symptoms of both subsided quickly with conservative treatment. In recent studies, bony gaps in the posterior arch are bridged by loose connective tissue rather than cartilage, suggesting that the anomaly is a result of defective development of the cartilage rather than disturbance of ossification per se.