Tension arachnoid cyst causing uncal herniation in a 60 year old: A rare presentation

Arachnoid cysts are congenital benign cysts accounting for approximately 1% of all intracranial mass lesions. Uncal herniation due to arachnoid cyst is a rare mode of presentation. It is hypothesized that only tension arachnoid cyst could cause the life-threatening condition that results from a progressive deterioration and worsening of a simple and usually congenital arachnoid cyst, associated with the formation of a "ball valve" at the point of an opening on the cyst wall. To-date only one case of an arachnoid cyst causing Uncal herniation has been reported to the best of our knowledge. We present a rare case of uncal herniation in a 60-year-old lady caused by a giant left temporal arachnoid cyst. She presented to us in emergency room after experiencing headaches since last one week followed by vomiting, seizures, and altered state of consciousness. She was operated immediately and marsupialization of the arachnoid cyst was performed. She showed good recovery. Although arachnoid cyst is a benign slowly growing pathology, it can lead to Uncal herniation as a "tension" arachnoid cyst, possible due to "ball-valve" mechanism. Elective treatment should be considered to prevent progressive significant enlargement of cyst.