Hemispherectomy is a surgery that is performed by a neurosurgeon where an unhealthy hemisphere of the brain is disconnected or removed. There are two types: Functional hemispherectomy refers to a simple surgical disconnection of the diseased hemisphere so that it can no longer send signals to the rest of the brain and body. Anatomical hemispherectomy refers to actual physical removal of the diseased hemisphere from the skull. This surgery is mostly used as a treatment for medically intractable epilepsy, which is the term used when anti-seizure medications are unable to control seizures.

History

The first anatomical hemispherectomy was performed and described in 1928 by the American Walter Dandy. This was done as an attempt to treat glioma, a brain tumor, and hemiplegia. The first known anatomical hemispherectomy performed as a treatment for intractable epilepsy was in 1938 by Kenneth McKenzie, a Canadian neurosurgeon. This marked a significant shift from tumor surgery toward the treatment of severe epilepsy.

In 1950, R.A. Krynauw in South Africa reported one of the earliest large case series in pediatric patients with infantile hemiplegia, demonstrating improvement in motor function, cognition, and seizure control. Despite these and other early successes, enthusiasm for the procedure declined by the late 1950s due to high rates of long-term complications such as superficial hemosiderosis, obstructive hydrocephalus, and progressive neurological decline. Oppenheimer and Griffith (1966) systematically described these adverse effects and highlighted the need for safer modifications.

In response, Theodore Rasmussen and others pioneered the functional hemispherectomy, which reduced the amount of brain tissue removed while disconnecting the epileptogenic hemisphere. This approach aimed to maintain seizure control while minimizing complications. European surgeons, including Delalande and Villemure, further refined disconnective procedures such as peri-insular hemispherotomy and vertical parasagittal hemispherotomy, which have since been widely adopted at epilepsy centers worldwide.

Over time, terminology has also evolved: while “functional hemispherectomy” was initially widely used, contemporary surgical literature increasingly favors the term “hemispherotomy” to describe modern disconnective approaches with minimal resection.

Oppenheimer and Griffith were one of the first to describe the potential complications, and they reported their findings in 1966, describing superficial hemosiderosis, granular ependymitis and obstructive hydrocephalus. They posited a theoretical solution to this problem, a surgery that is now known as a functional hemispherectomy. -->

Nomenclature

There are two principal forms of hemispherectomy: anatomical and functional.

  • Anatomical hemispherectomy involves removal of nearly the entire cerebral hemisphere, including all four lobes, with or without excision of the basal ganglia and thalamus.

In recent decades, the term “hemispherotomy” has been adopted to describe a group of modern disconnective surgeries that achieve functional isolation of the epileptogenic hemisphere with minimal brain removal. Variants such as the peri-insular hemispherotomy and vertical parasagittal hemispherotomy are now widely practiced, and are often considered the contemporary standard at major epilepsy centers.

Emerging minimally invasive variations, including endoscope-assisted hemispherotomy, have been reported in select centers, though these remain experimental and are not yet considered standard of care. However, they do carry a risk of incomplete disconnection, which refers to when the surgeon inadvertently leaves remnants of fibers that continue to connect the hemisphere to the brain and body. These remaining fibers can be problematic, as they may lead to seizure recurrence.

Another term that falls under the hemispherectomy umbrella includes hemidecortication, which is the removal of the cortex from one half of the cerebrum, while attempting to preserve the ventricular system by maintaining the surrounding white matter. Hemidecortication was originally developed as a possible strategy to mitigate some of the complications seen with complete anatomical hemispherectomy. The most common underlying etiologies include malformations of cortical development (MCD), perinatal stroke and Rasmussen's encephalitis. A recently developed scoring system has been proposed to help predict the probability of seizure freedom with more accuracy:  HOPS (Hemispherectomy Outcome Prediction Scale).

In terms of postoperative motor function, some patients may have improvement or no change of their weaker extremity, Predictors of poor outcome may include seizure recurrence and structural abnormalities in the intact hemisphere.

See also

  • Corpus callosotomy
  • Hemispherectomy Foundation

References

Further reading

  • The Deepest Cut by Christine Kenneally, The New Yorker