[Arachnoid cysts: histologic, embryologic and physiopathologic review].

Arachnoid cysts form a cavity containing a cerebrospinal-like fluid, the wall of which is composed of arachnoidal cells. Other types of intracranial cysts have been described, they differ from arachnoid cysts by the histological characteristics of their wall. To analyze homogeneous series, it is thus necessary to differentiate arachnoid cysts from the other types of cysts. Several localizations of these lesions have been described: the most frequent being the temporo-sylvian area. Arachnoid cysts are considered as resulting from congenital malformations that can change during postnatal life. They can no longer be considered as resulting from cerebral atrophy. This arachnoid malformation could be the primary event or be explained by an impairment of the cerebrospinal fluid drainage generated by venous agenesis. Several mechanisms could account for the inflation of these cysts: secretion by the cells forming the cyst walls, unidirectional valve, liquid movements secondary to pulsations of the veins.