of the hemisphere and disconnecting the rest. This resulted in a much lower rate of complications but less effective seizure control, which led Rasmussen to further modify the technique by removing only the central part of the brain and disconnecting the frontal and occipital parts. He called this approach “functionally complete-anatomically total” hemispherectomy. The seizure control results were comparable to anatomical hemispherectomy whereas the complication rate was very low. Later, further modifications were implemented, all aiming at minimizing the amount of brain tissue removed and instead disconnecting it, including central parasagittal hemispherectomy by Delalande in 1992, periinsular hemispherectomy by Villemure, and transylvian hemispherectomy by Schramm The differences between these techniques was the surgical window used to perform the disconnection, but they all shared excellent seizure outcomes of 80-90% of patients becoming seizure free and minimal complications. These mostly disconnective techniques are now collectively referred to as functional hemispherectomy or hemispherotomy. The surgical access that is typically used to perform a hemispherectomy is through a craniotomy, which involves making a window in the skull. More recently introduced techniques aim at minimizing tis surgical access by utilizing small burr holes to perform “endoscopic hemispherectomy” using either special endoscopic tools. or laser probes to perform the disconnection. Causes of hemispheric epilepsy There is a heterogeneous group of pathologies that could cause hemispheric epilepsy and these are typically divided into 3 groups. The first group is congenital pathologies which means that the patient is born with hemisphere that is malformed with abnormal cortex that is capable of seizing. Examples of such pathologies include focal cortical dysplasia, pending megaloencephaly, package area among others. The second group of etiologies is called acquired where an insult or an injury to one half of the brain is sustained early in life, usually around birth. Such etiologies include strokes that affect 1 hemisphere of the brain, hemorrhage (bleeding) or trauma. The third group is termed progressive etiologies and this group includes diseases that develop later in life with a protracted and progressive course. Such etiologies include Rasmussen's encephalitis, Sturge-Weber syndrome and hemispheric brain tumors. All these causes of hemispheric epilepsy have the common feature of a widespread pathology that is strictly or mostly restricted to one hemisphere. Hemispherectomy workup and patient selection Patients who have drug-resistant focal epilepsy defined as failing 2 or more medications with seizures arising from 1 hemisphere of the brain qualify to be candidate for