Dorsal craniovertebral junction arachnoid cyst

Arachnoid cysts causing symptoms, at the level of the craniovertebral junction (CVJ), are very infrequently reported. Inadequate imaging (either only of brain up to foramen magnum or only cervical spine) often leads to delayed diagnosis in these cases. Those that straddle the CVJ do not cause tonsillar descent and differ from the more common pure retro or supracerebellar posterior fossa cysts that cause tonsillar descent, although they present in an identical manner. We treated the index case by fenestration of the lower end of the cyst into the spinal subarachnoid space instead of the more extensive surgeries hitherto described as we felt that cerebrospinal fluid flow patterns with an intact foramen magnum and help conferred by gravity would prevent re-accumulation.