Arachnoid Cyst

Arachnoid Cysts

Arachnoid Cysts

Arachnoid cysts are the benign cysts in the cerebrospinal axis. These cysts usually occur in association with arachnoid cisterns. These cysts are congenital and diagnosed accidentally. Some time they are formed due to surgery and infections. The symptoms may include headache, bulging, l hypertension, visual loss, and seizures. If this cyst is not causing problem then there is no need of surgery. Even large size of these cysts does not cause problems.

Arachnoid cysts are more common in males with a ratio of 2:1   and are more frequently seen within the left hemisphere than the right ; however, there is no definite known cause for the left sided predominance nor their tendency to occur more frequently in the male population. Interestingly, studies of arachnoid cysts discovered antenatally and followed in the neonate, have often found them to undergo spontaneous regression and only progress in rare instances. 

Diagnosis of Arachnoid Cysts

From the diagnostic point of view, arachnoid cysts are typically a serendipitous discovery on imaging studies. On CT, they typically appear as extra-axial CSF density lesions causing local space occupying effect and occasionally calvarial remodeling.

CT can be helpful to identify a cyst complicated by internal haemorrhage as the quickest and most readily available neuroimaging test. However, MRI is the definitive diagnostic tool for evaluation of arachnoid cysts as it confirms the extra-axial location and shows homogenous T2-weighted signal hyper intensity within the cyst similar to that of CSF.  


Arachnoid cysts are most commonly an incidental discovery on neuroimaging and have for the most part, a benign natural history. They comprise 1% of intracranial masses and are more common in males. Increasingly, arachnoid cysts are being discovered at earlier ages due to more widespread use of antenatal and cross-sectional imaging. For the few that cause symptoms, their clinical presentation will depend on their location and the adjacent structures onto which they cause mass effect on. They also may present with hemorrhage or rupture. Treatment is generally reserved for symptomatic cysts with a range of neurosurgical techniques available 

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