Pathogenesis of intracranial arachnoid cysts.

The pathogenesis of intracranial arachnoid cysts is reviewed. Light and electron microscopic features of arachnoid cysts are presented in support of the hypothesis of Starkman et al, that these cysts are truly intraarachnoid in location and are formed by splitting or duplication of the arachnoid membrane. Documentary evidence is provided to prove that Richard Bright's original description in 1831 contains these concepts, which have passed unnoticed for nearly a century and a half. A brief description of the meninges and the subarachnoid spaces is given.