Evidence against association between arachnoid cysts and epilepsy.

Arachnoid cysts are often discovered incidentally in MRs performed for a variety of reasons. In this study, we have attempted to determine a possible relationship between the arachnoid cyst, seizure type and EEG abnormalities. Eight patients were classified according to the Classification of Epilepsies and Epileptic Syndromes of ILAE as idiopathic generalized or localized epilepsy: three as idiopathic generalized epilepsy, three as Rolandic epilepsy and two as juvenile myoclonic epilepsy. Two patients with rare nocturnal seizures had normal EEGs in the awaking and sleep stage. The EEGs of five patients with simple or complex partial seizures revealed focal epileptiform abnormalities, but only one patient had the same location with the arachnoid cyst. Five patients with symptomatic epilepsy had diffuse slowing in their EEGs and only one patient had seizure focus in the EEG that was contralateral to the arachnoid cyst. According to our study, seizure type and EEG abnormality corresponds to arachnoid cyst location in only one patient. Therefore, we suggest that arachnoid cysts may not be related to a specific seizure type and EEG focus.