Four patients out of 52 patients with
temporal lobe epilepsy (TLE), who underwent
epilepsy surgery in our hospital since September of 1994, had cystic lesions in the temporal lobe and middle cranial fossa. Case 1 had old
hematoma cavity in the inferior temporal gyrus and chronic subdural
electrode recording revealed the ictal onset zone to be localized in the ipsilateral medial temporal region. Case 2 had cystic
ganglioglioma in the temporal tip, and intraoperative electrocorticography demonstrated independent paroxysmal activities from medial temporal region and temporal tip near the
cyst. Both area were resected and the patients became seizure free. Case 3 and 4 had
arachnoid cysts in the middle cranial fossa. Chronic subdural
electrode recording revealed that the ictal onset zone was localized in the ipsilateral inferior temporal gyrus (that had microdysgenesis) in Case 3 and contralateral medial temporal region (that had
hippocampal sclerosis) in Case 4, respectively. These finding suggest that co-existence of extra-axial
cyst such as Case 3 and 4 is incidental and that arachnoid
cyst is less epileptogenic. However, intra-axial
cyst such as Case 1 and 2 is epileptogenic and complicated physiological mechanism such as kindling phenomenon or secondary epileptogenesis may effect on the hippocampus. Comprehensive presurgical evaluation including electrocorticography is needed in the surgical treatment of TLE with cystic lesion.