Some children with infantile spasms have large brain abnormalities affecting an entire hemisphere, i.e. the left or right half of the brain. Common examples include large focal cortical dysplasias (FCD), large strokes, hemimegalencephaly, and Rasmussen encephalitis. A hemispherectomy is an operation in which one half of the brain is removed.

Like smaller focal lesions, these larger abnormalities are similarly confirmed and characterized by a variety of neurodiagnostic tests including electroencephalography (EEG), magnetic resonance imaging (MRI), positron emission tomography (PET) or single photon emission computed tomography (SPECT), and magnetoencephalography (MEG). In some cases, additional studies are needed as well, including invasive electrical monitoring with depth electrodes or electrocorticography (ECoG), functional magnetic resonance imaging (fMRI), or the WADA test (a procedure in which a portion of the brain is temporarily "inactivated" by a medication to simulate a post-surgical state). These studies aim to determine the structural and functional characteristics of the lesions, both during seizures (ictal), and in between seizures (interictal).

If a large abnormality is identified and deemed appropriate for surgical removal with hemispherectomy, excellent rates of seizure-freedom are possible in select patients. Hemispherectomy operations are often performed when more limited resections are unsuccessful. However, as you may imagine, removing half of a brain is no small task, and carries significant operative and postoperative risks. In older children and adults, loss of one-half of the brain can have a major impact on control of movement and sensation on the opposite side of the body, vision on the opposite side, speech and language production and comprehension, memory, personality, mood, decision making capacity, and many other subtle and sophisticated neurological functions. Though in young children, as well as older children and adults with long-standing hemispheric dysfunction (one half of the brain not performing well), the risks are much smaller. In fact, among very young children, amazing recovery of these functions is often possible—so much so that with recovery and rehabilitation, a casual observer can't tell such a surgery had been performed. As is the case when considering any epilepsy surgery, the risks and benefits must be very carefully considered. As is the case in considering focal resections (discussed elsewhere), a multidisciplinary team including neurologists (epileptologists), neurosurgeons, neuroradiologists, neuropsychologists, and others must consult with parents and patients to decide if a given patient is a candidate for hemispherectomy.

As mentioned elsewhere, surgery to remove brain regions generating seizures is not a therapy of last resort. In general, if a patient has failed therapy with several well-chosen medications, surgery may be considered depending on risks and benefits of the procedure—including the risk of not performing surgery.

News stories regarding hemispherectomy at UCLA:



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