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  • Updated 03.21.2019
  • Released 09.13.1995
  • Expires For CME 03.21.2022

Arachnoid cyst



The authors review 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). Arachnoid cysts are usually intracranial and supratentorial in location, but spinal, and even intraneural, cysts may be identified and possibly cause symptoms. Asymptomatic cysts do not require active management. However, some are associated with seizures, local pressure effects, or hydrocephalus and may require treatment. 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. Surgical intervention 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. In over 40% of patients, some other underlying condition on the differential diagnosis, and not the arachnoid cyst, was revealed to be the cause of the symptoms.

• 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%).

• A systematic review of published case reports for individuals with arachnoid cysts who suffered a structural brain injury during a sport or recreational activity did not find evidence to support recommending against participation in sports for patients with arachnoid cysts.

Historical note and terminology

Arachnoid cysts are classified as developmental cysts; they were first described in 1831 (10). These cysts lie between 2 membranes of normal arachnoid matter and are more properly described as intra-arachnoid cysts (101). 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) (113).

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 (60). One of the first successful surgical interventions for an arachnoid cyst was a partial removal by Placzek and Krause in 1907, resulting in clinical improvement (78). The traditional surgical approach to arachnoid cyst, namely removal of as much of the cyst wall as was possible (56), 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 (103).

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