The dramatic procedure of hemispherectomy originally involved the removal of one whole side of the brain. Now, it usually involves disconnecting one cerebral hemisphere from the rest of the brain, with removal of only a limited area.
It is only considered in patients, usually children, with severe epilepsy in whom seizures arise from only one side of the brain and in which that hemisphere functions poorly. Before surgery, these patients typically have severe weakness (paralysis) and loss of touch sensation and vision on the opposite side of the body. Therefore, the side of the brain that is to be disconnected is already functioning very poorly and often impairs the functions of the other side of the brain. If the operation is performed on young children, the opposite hemisphere may make up for the loss.
One major consequence of hemispherectomy is that the patient will never have movement or normal sensation in the hand, forearm, foot, and leg on the side opposite the operation. However, controlled movements are possible in the upper arm and thigh, thus permitting the person to walk. Physical therapy is often needed after hemispherectomy.
The results of hemispherectomy are quite good. More than 75% of the patients experience complete or nearly complete seizure control. If the patient has a progressive disorder, such as Rasmussen’s syndrome, the prognosis for seizure contro is less good.