Arachnoid cysts can be intra-cranial or along the spinal cord.Intracranial arachnoid cyst is a very rare finding, trauma being the leading case of it.It is extremely rare for the development of intra-diploic arachnoid cyst without a traumatic click here history.We present a case of an intra-diploic arachnoid cyst communicating with the greater wing of the sphenoid and in close proximity to the cavernous sinus in a known case of Wilson disease for 22 years.Due to its low incidence, there is a gap in the knowledge and discussion of this cystic lesion, its pathophysiology and management, which are discussed powell and mahoney bloody mary mix in this case report.