Symptomatic spinal arachnoid cyst triggered by seat belt injury--case report.

A 49-year-old male presented with a symptomatic thoracic intradural arachnoid cyst triggered by seat belt trauma, which appeared within 3 weeks following a traffic accident. The initial symptom was a dull back pain induced immediately after the accident. Three and half months later, magnetic resonance (MR) imaging diagnosed the cystic nature of the lesion consistent with a low intensity on T1-weighted image which extended dorsally between the T-4 and T-6 levels. One month later, MR imaging showed that this cystic mass had enlarged in the anteroposterior direction associated with developing clinical symptoms. The final diagnosis of arachnoid cyst was made based on surgical findings and histological examinations. The spinal arachnoid cyst was probably a congenital arachnoid cyst or diverticula originating from the septum posticum which became enlarged due to sudden increase of intra-abdominal pressure caused by the fastened seat belt during the accident.