[A case report of an arachnoid cyst in the craniovertebral junction].

We reported a case of arachnoid cyst in the craniovertebral junction which was extremely rare. A 36-year-old man presented truncal ataxia and dysesthesia in the right upper extremity. CT and MR images revealed a large cyst in the craniovertebral junction. As for findings of MR images, cystic lesion showed similar intensity as cerebrospinal fluid. Intradural arachnoid cyst with thickened dura was opened to communicate with subarachnoid space. Fluid in the cyst was watery clear. Histological finding of the surgical specimen was arachnoid cyst without inflammatory changes. Arachnoid cyst in the craniovertebral junction is discussed with literature.