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 American neurosurgeon 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. With advances in neuroimaging and perioperative monitoring, hemispherectomy regained prominence in the 1980s and 1990s, as outcomes became more predictable and patient selection improved. 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. Today, hemispherotomy techniques are regarded as the contemporary standard, associated with improved safety profiles and long-term seizure freedom in carefully selected patients.
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. Functional hemispherectomy disables the diseased hemisphere by disconnecting its cortical and subcortical pathways while leaving much of the brain tissue in place and maintaining vascular supply. This approach is preferred in most modern centers because of its lower complication rates, although incomplete disconnection can result in seizure recurrence. Another related procedure is hemidecortication, which removes only the cerebral cortex of one hemisphere while sparing deeper white matter and ventricular structures. It was initially developed as an attempt to reduce complications associated with full anatomical hemispherectomy. 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. Contemporary classification emphasizes the degree of functional disconnection rather than the absolute volume of tissue removed, reflecting the shift toward minimally invasive strategies. In clinical literature, the terms "functional hemispherectomy" and "hemispherotomy" are occasionally used interchangeably, although most modern authors reserve "hemispherotomy" for the newer disconnective approaches. 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. Systematic reviews indicate that seizure-free rates are similar across anatomical hemispherectomy, functional hemispherectomy, hemidecortication, and hemispherotomy (approximately 70–75%). However, hemispherotomy generally carries a more favorable complication profile. Recent ILAE surgical task force reports support hemispherotomy as the preferred modern terminology and technique in most cases.
Candidates The typical candidates for hemispherectomy are pediatric patients with drug-resistant epilepsy caused by extensive unilateral cerebral pathology. In these cases, seizures predominantly arise from one hemisphere, and medical therapy is ineffective. Although bilateral seizure activity may occasionally be observed, surgery can still be considered if one hemisphere is clearly the dominant source of seizures.Preoperative evaluation is comprehensive and usually includes prolonged video electroencephalography (EEG) and high-resolution magnetic resonance imaging (MRI). Additional studies such as functional MRI (fMRI), positron emission tomography (PET), and magnetoencephalography (MEG) are frequently employed to refine localization and lateralization of the epileptogenic focus. Today, hemispherectomy is performed as a treatment for severe and intractable epilepsy, including for young children whose epilepsy has been found to be drug-resistant. The most common underlying etiologies include malformations of cortical development (MCD), perinatal stroke and Rasmussen's encephalitis. MCD is an umbrella term for a wide variety of developmental brain anomalies, including hemimegalencephaly and cortical dysplasia. Other less common underlying etiologies include hemiconvulsion-hemiplegia epilepsy syndrome and Sturge-Weber syndrome.
… excerpt ends here. Continue reading the full article.
