Abstract
Arachnoid cysts are common in the younger generation and most commonly found in the middle fossa, while those in the interhemispheric fissure have been rarely reported. Two adult cases of arachnoid cyst, one within the interhemispheric fissure and another one over the cerebral convexity, are presented. Protein content of the cyst fluid, 19.6 mg/dl and 9.0 mg/dl, respectively, was lower than that of the lumbar cerebrospinal fluid in each case.
Coexisting defects of the brain are not likely to represent the primary process; they seem to be the secondary results of an expansion of the cyst. The primary arachnoid cyst seems to be caused by a developmental error on the side of the arachnoid and not on the side of cerebral tissue.
