Hemispherectomy

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 term hemispherotomy refers to a surgery that is akin to a functional hemispherectomy in that it functionally severs the damaged hemisphere from the other and leaves some of the severed hemisphere within the skull, but the difference is that it removes even less tissue from the skull. The term hemispherotomy is now used as an umbrella term to describe the group of modern techniques and procedures that predominate at most contemporary epilepsy centers. There is no statistically significant difference in seizure-free rates between the four different types of surgeries: Hemispherotomy, functional hemispherectomy, anatomical hemispherectomy and hemidecortication. The overall rate of seizure freedom is estimated to be 73.4%. However, hemispherotomy procedures may be associated with a more favorable complication profile. --> == Candidates ==

The typical candidates for hemispherectomy are pediatric patients with drug-resistant epilepsy caused by extensive unilateral cerebral pathology. 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. == Procedure ==

Patients often shave the area of the scalp that will be involved with the surgery. Patients undergo general anesthesia and are unconscious for the procedure. The surgical site is sterilized, after which the skin is incised. A substantial portion of the bone is removed, followed by incision of the dura, which is the outer covering of the brain. There are several blood vessels that have connections with both sides of the brain, and these are carefully identified and clipped in such a way that spares the healthy hemisphere. Ultimately, a bundle of fibers that connect both of the cerebral hemispheres, the corpus callosum, is removed which results in the functional separation of one hemisphere from the other. Portions of the cerebral lobes from the damaged side of the brain are removed, depending on the specific procedure being performed. The surgeon may leave some brain tissue, such as the thalamus or choroid plexus. After completing the resection, the surgical site is irrigated with saline, the brain covering called the dura is sutured back together, the bone that was removed is replaced and the skin is sutured. This surgery often takes four to five hours. Patients often spend a few nights in the hospital post-operatively, and they undergo physical and occupational therapy soon after the surgery. == Potential complications ==

The most common complication from surgery is hydrocephalus, a condition in which fluid accumulates within the brain, and this is often treated with a shunt to divert the fluid away. The rate of shunts following surgery ranges from 14 to 23%. Other complications include wound complications, epidural hemorrhages, subdural hemorrhages, intraparenchymal hemorrhages, intracranial abscesses, meningitis, ventriculitis and venous thrombosis. Additional epilepsy surgery following hemispherectomy is rare (4.5%), but may be recommended if there is a residual connection between the two hemispheres that is causing frequent seizures. Mortality rates are low and estimated to be <1% to 2.2%. Most patients do not experience changes in cognition, but some individuals may be at risk. A visual deficit called contralateral homonymous hemianopsia is expected to occur in most patients, where the entire visual field contralateral to the removed hemisphere is lost. There is a risk of motor deficits, and this is variable. Other possible complications include infection, aseptic meningitis, hearing loss, endocrine problems and transient neurologic deficits such as limb weakness. == Outcomes ==

Since seizures are the most common indication for hemispherectomy surgery, most research on hemispherectomy analyzes how the surgery affects seizures. Many patients undergoing surgery obtain good surgical outcomes, some obtaining complete seizure freedom (54–90%) and others having some degree of improvement in seizure burden. 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 ==