“Idiopathic seizures are those whose cause is unknown. Unfortunately, about 6 out of 10 seizures are idiopathic. In the case of focal seizures, we presume that there is an irritation to or scar on some part of the brain, but the scar is invisible to MRI. With generalized seizures, the genetic or metabolic abnormality is unidentified.”
Epilepsy Foundation (epilepsy.com)