Of 28 cases of intracranial arachnoidal cysts reported from the Clinica Las Condes, Santiago, Chile, 17 were located in the middle cranial fossa, 3 in the quadrigeminal cistern, 2 were parasagital, 3 suprasellar and 3 were in the posterior fossa. Of 23 (82%) treated surgically, 3 received craniotomy with fenestrations, 8 had shunts and 15 were treated by the insertion of cystoperitoneal drainage with excellent results. Twenty-one of the 22 treated cases are asymptomatic and leading a normal life. MRI or CT follow-up showed disappearance of cysts in 14 and marked reduction in size in 7. 
COMMENT. The diagnosis of intracranial arachnoidal cysts and reports in the literature have become more frequent since the routine use of neuroimaging. The danger of intracystic hemorrhage with a high possibility of secondary hydrocephalus following head injury has been quoted as a reason for surgical intervention, as a preventive measure in some cases. See Ped Neur Briefs Oct 1991, 5:80 for a report of 67 childhood arachnoidal cysts treated surgically and 1 report of spontaneous disappearance of a cyst. Small or medium sized cysts without clinical manifestations are not usually treated but are monitored carefully.