Craniocervical junction arachnoid cyst causing hydrocephalus: case report and review of the literature.

<bold>Objective: </bold>Arachnoid cysts (ACs) of the craniocervical junction are extremely rare entities. This report describes a craniocervical junction AC with unusual clinical course at an unusual anatomical location.<bold>Methods: </bold>A 21-year-old man was admitted to our clinic after a craniospinal trauma. Examination was unremarkable. Computed tomography scans demonstrated mild to moderately enlarged third and the lateral ventricles, but the fourth ventricle was typically normal. Neuroimaging studies obtained after the onset of clinical symptoms revealed marked enlargement of the ventricular system and a new cyst formation at the C1-2 level which was absent before. He underwent suboccipital craniectomy and C1-2 laminectomies. The cyst was fenestrated into subarachnoid space.<bold>Results: </bold>He made a good recovery. The histopathological diagnosis was confirmed as AC.<bold>Conclusion: </bold>Due to rarity of this clinical entity, we urge readers to keep in mind the possibility of the development of this kind of AC with unusual clinical course. [ABSTRACT FROM AUTHOR]