Arachnoid cyst

Robert Grant MD (Dr. Grant of the Edinburgh Centre for Neuro-Oncology has no relevant financial relationships to disclose.)
Edward J Dropcho MD, editor. (Dr. Dropcho of Indiana University Medical Center has no relevant financial relationships to disclose.)
Originally released September 13, 1995; last updated April 20, 2015; expires April 20, 2018


The author reviews the etiology, presentation, investigation, and treatment of arachnoid cysts in the brain and spine. Arachnoid cysts are common incidental findings (1.4% of adults and 2.5% of children having an MRI scan). Asymptomatic cysts should be left alone. Some are associated with seizures, local pressure effects, or hydrocephalus. Urine should be checked for glutaric acid in cases of bitemporal arachnoid cysts as glutaric aciduria type 1 is present in 25% of cases. Symptomatic cysts will require intervention in the presence of hydrocephalus or spinal cord compression. Operation to treat seizures or headache is successful in only 33% to 50% of cases. Electroencephalographic seizure focus coinciding with temporal arachnoid cyst and SPECT imaging demonstrating impaired cerebral perfusion may be helpful when considering intervention. Minimally invasive neuroendoscopic techniques are being more widely practiced where there is hydrocephalus or suprasellar cysts, but resection and marsupialization for large Sylvian fissure and cortical arachnoid cysts has superior success rates to neuroendoscopic procedures. Endoscopic fenestration, although less effective at reducing cyst size, has a lower complication rate. The complication rate of fenestration of arachnoid cysts in pediatric cases is over 35%. About 10% of arachnoid cysts recur after fenestration, and subdural hygromas requiring re-operation occur in 6% of all cases of large Sylvian fissure arachnoid cysts.

Key points


• Be certain that the cyst is responsible for symptoms before considering intervention.


• Arachnoid cysts in children are as likely to decrease in size as they are to increase.


• Two thirds of cases are temporal fossa arachnoid cysts.


• There may be rupture of bridging veins or vessels in the wall of the cyst, which can result in subdural hematoma or bleeding into the cyst.


• Endoscopic procedures for temporobasal arachnoid cysts have the lowest success rate (81%), highest recurrence (19%), and highest complication rate (24%).

Historical note and terminology

Arachnoid cysts are classified as developmental cysts; they were first described in 1831 (Bright 1831). These cysts lie between 2 membranes of normal arachnoid matter and are more properly described as intra-arachnoid cysts (Starkman et al 1958). Congenital or developmental arachnoid cysts differ from secondary or acquired arachnoid cysts, as the latter are loculations of CSF surrounded by arachnoid scarring. A classification of midline cysts based on neuroembryologic analysis and imaging, suggests 2 categories:

Category 1: Expansion of the roof plate of the brain vesicle (eg, Dandy Walker cyst, Blake pouch cyst, communicating interhemispheric cysts with callosal agenesis, or dorsal cyst with holoprosencephaly).

Category 2: Cysts consisting of extra-axial structures, eg, arachnoid membrane or migrating ependymal cells (arachnoid cyst, arachnoid pouch, mega cisterna magna) (Utsunomiya et al 2006).

One of the first successful operations was a partial removal of an arachnoid cyst by Placzek and Krause in 1907; the patient was improved by the operation (Placzek and Krause 1907). The traditional surgical approach to arachnoid cyst, namely removal of as much of the cyst wall as was possible (Matson 1969), was often complicated by damage to the surrounding brain and cyst recurrence. Although shunting recurrent cysts was often successful, shunt insertion as primary treatment was only first advocated in 1981 (Stein 1981). Suprasellar arachnoid cysts have been classified as noncommunicating intra-arachnoid cysts of the diencephalic membrane of Liliequist as well as communicating cystic dilations of the interpeduncular cistern, based on MRI, CT cisternograms, and neuroendoscopy (Miyajima et al 2000).

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