top of page



In the context of neurology, Hemispherectomy refers to a surgery in which half of the brain (called ahemisphere, or cerebral hemisphere) is removed; either physically or functionally.


  • Word origins

    • hemi - is the root for half

    • sphere - comes from the Greek word sphaira, meaning "globe" or "ball", and refers to the brain

    • -ectomy comes from the Greek -ektomia, meaning "a cutting out of"

    • -otomy - is a medical suffix from Greek tome, meaning "a cutting"

  • Anatomic hemipherectomy refers to complete removal of half of the brain

  • Functional hemispherectomy refers to disconnection of half of the brain without removal of the tissue


There are two types of hemispherectomy:

  1. functional and

  2. anatomic


Anatomic hemispherectomy: refers to disconnecting and fully removing the hemisphere. Historically, this was the way the surgery was initially performed, but is now rare due to late complications that can be avoided if the brain is disconnected, but left in place (see below). The complications (which functional hemispherectomy can reduce), are hydrocephalus and hemorrhage.


Functional hemispherectomy (or hemispherotomy): refers to the disconnection of the hemisphere from the rest of the brain and body. The brain tissue itself is not removed. Because they still have a blood supply, the brain cells do not die, but they are functionally inert. This is possible because brain cells send signals to their neighbors over long wire-like extensions called axons. In a functional hemispherectomy, the axons are severed, and no nerve signals can be sent. Therefore it achieves the same purpose as (and has similar side effects to) complete removal. It may be more accurately called a hemispherotomy, but most use the terms interchangeably.


Hemispherectomy is primarily used to treat epilepsy which is:

  • Not controlled by medication

  • More conservative surgery would not effectively treat the epilepsy

  • The opposite half of the brain is normal, or has low epileptic potential


Some of these factors can be difficult to determine.

In some cases, hemispherectomy can completely eliminate the seizures, and is a surgical cure for the epilepsy in question. A common type of epilepsy for which hemispherectomy is the definitive (and usually inevitable) treatment is Rasmussen's encephalitis (also called chronic focal encephalitis).

bottom of page