One region gives rise to seizures but the other does not. Cortical dysplasia tends to spare the hippocampal formation and principally affects the neocortex. Cortical gliosis can occur following any brain injury - trauma, infection. Traumatic insults which produce epilepsy are more frequent with lesions that penetrate the skull and particularly those which penetrate the dura . These areas are recognized by cystic changes within the brain parenchyma with loss of volume of adjacent brain.
Partial epilepsy tends to be associated with cavernous hemangiomas and arteriovenous malformations.
Seizures may in fact be the only clinical manifestation with these lesions. AVMs are typically be associated with irregular looking flow voids. Familial cavernous hemangiomas are inherited as an autosomal dominant trait. During a seizure, there may be a 3-4 fold in cerebral blood flow. This means that a scan done several hours after the injection will reflect blood flow at the time of injection.