Hemispherectomy

Hemispherectomy is a very rare surgical procedure in which one cerebral hemisphere (half of the brain) is removed, disconnected, or disabled. This procedure is used to treat a variety of seizure disorders where the source of the epilepsy is localized to a broad area of a single hemisphere of the brain, notably Rasmussen's encephalitis. About one in three patients with epilepsy will continue to have persistent seizures despite epileptic drug therapy.^[1] Hemispherectomy is reserved for the most extreme cases of this one-third in which the individual’s seizures are irresponsive to medications or other less invasive surgeries and significantly impair functioning or put the patient at risk of further complications. The procedure successfully cures seizures in about 85%-90% of patients. Additionally, it is also known to often markedly improve the cognitive functioning and development of the individual.^[2]

History and Development

Hemispherectomy was first performed on a dog in 1888 by Friedrich Goltz. The first such operation on humans was done by Walter Dandy in 1923 for glioblastoma multiforme. Hemispherectomy was revitalized in children in the 1980s by Ben Carson at Johns Hopkins Hospital.^[3]

In the 1960s and early 1970s, hemispherectomy involved essentially removing an entire half of the brain. This procedure is known as anatomical hemispherectomy. Anatomical hemispherectomy decreases the likelihood that seizures will return, as there is no longer any part of the identified epileptic brain area left to cause seizures. A second type of hemispherectomy, known as functional hemispherectomy, has become more prevalent in recent years. In this procedure, only the epileptic portions of that side of the brain are removed, as opposed to the entire hemisphere. If a functional hemispherectomy is chosen over an anatomical hemispherectomy, it is likely because it allows for less blood loss and greater chance of resilience for the patient.^[4][5] Additionally, functional hemispherectomy is less likely to cause hydrocephalus, the “excessive accumulation of (cerebrospinal) fluid in the brain,” which leads to complications from harmful pressure on brain tissues.^[6]

Within the last fifteen years, a few types of functional hemispherectomies have emerged. One such procedure is known as peri-insular hemispherectomy. Peri-insular hemispherectomy has been developed to allow for seizure relief with minimal brain tissue removal. In this procedure, the surgeon aims to disconnect (rather than remove) the hemisphere, in order to minimize long term complications.^[7] Another procedure relatively new to epilepsy surgery is endoscopic surgery (see endoscopy), surgery performed using small camera scopes and little incision sites. Its appeal lies in its minimally invasive nature, which generally decreases chance of infection and increases speed of physical recovery.^[8]

Patient Criteria

Because of the dramatic alteration of brain composition and the inherent risk that hemispherectomies pose, there are criteria that must be met in order for a person to qualify for the procedure. Criteria include no successful control of seizures throughout a variety of drug trials, and a reasonable to high chance of procedural success.^[9]

One such predictor of success is often the age of the patient. This procedure is almost exclusively performed in children because their brains generally display more neuroplasticity, allowing neurons from the remaining hemisphere to take over the tasks from the lost hemisphere. This likely occurs by strengthening neural connections which already exist on the unaffected side but which would have otherwise remained small in a normally functioning, uninjured brain.^[10] In one study of children under 5 who had this surgery to treat catastrophic epilepsy, 73.7% were freed of all seizures.^[11]

Success of the procedure is not, however, limited to children. A study in 2007 indicated the long-term efficacy of anatomic hemispherectomy in carefully selected adults, with seizure control sustainable over multiple decades.^[12] A case study published in 2015 of 2 adults aged 48 and 38 demonstrated the success of functional hemispherectomy in treating status epilepticus (SE), an epileptic condition in which seizures are prolonged or occur closely together.^[13] In 2012, a case study following 30 individuals having undergone some form of hemispherectomy in adulthood found that 81% of individuals were seizure free post-procedure. Furthermore, almost all participating patients reported improved quality of life. The conclusion: “(a)dult patients do not have to expect more problems with new deficits, appear to cope quite well, and mostly profit from surgery in several quality of life domains.”^[14]

Ultimately, the chances of benefit and improvement to the individual must outweigh the costs. For example, a neurosurgeon would not recommend hemispherectomy in a patient who still possessed significant functionality, despite frequent seizures. Such a patient would risk losing their remaining functionality. Likewise, hemispherectomy likely would be recommended to a patient with debilitating seizures. A patient with little or severely deteriorating functioning does not have as much to risk by having the procedure, thus the chance of benefit to them is greater.^[15] Depending on the case, a recommendation for a hemispherectomy could be more risky than for a child than for an adult. Thus, age is not always the deciding success factor for hemispherectomies.

Results

Overall, hemispherectomy is a successful procedure. A 1996 study of 52 individuals who underwent the surgery found that 96% of patients experienced reduced or completely ceased occurrence of seizures post-surgery.^[16] Studies have found no significant long-term effects on memory, personality, or humor,^[17] and minimal changes in cognitive function overall.^[18] For example, one case followed a patient who had completed college, attended graduate school and scored above average on intelligence tests after undergoing this procedure at age 5.5. This patient eventually developed "superior language and intellectual abilities" despite the removal of the left hemisphere, which contains the classical language zones.^[19]

When resecting the left hemisphere, evidence indicates that some advanced language functions (e.g., higher order grammar) cannot be entirely assumed by the right side. The extent of advanced language loss is often dependent on the patient's age at the time of surgery.^[20] One study following the cognitive development of two adolescent boys who had undergone hemispherectomy found that “brain plasticity and development arise, in part, from the brain’s adaption of behavioral needs to fit available strengths and biases…The boy adapts the task to fit his brain more than he adapts his brain to fit the task.”^[21] Neuroplasticity after hemispherectomy does not imply complete regain of previous functioning, but rather the ability to adapt to the current abilities of the brain in such a way that the individual may still function, however differently the new way of functioning is.

Along with neuroplasticity, people who undergo hemispherectomies remarkably recover due to resilience. Resilience is the ability, in this case, of the brain being able to recover from a tough situation and take back its shape. Neuroplasticity resilience explains why the hemisphere that is still intact is able to recover many of the functions that were once the removed hemisphere's job. Resilience here is an action in patients with hemispherectomies in which they recover and navigate back to health.^[22]

Traumatic Hemispherectomy

There are cases where a person that received major trauma to one side of the brain, such as a gunshot wound, has required a hemispherectomy and survived. The most notable case is that of Ahad Israfil, who lost the right side of his cerebrum in 1987 in a gun-related work accident. He eventually regained most of his faculties, though he still required a wheelchair. It was noted that reconstructive surgery was difficult due to the gunshot shattering his skull, and he is living with a large indentation on that side of his head.

See also

• Corpus callosotomy
• Hemispherectomy Foundation
• Epilepsy

References

External links

• Johns Hopkins Children's Center research findings
• Hopkins Medical News article on the topic
• The Hemispherectomy Foundation
• The Deepest Cut by Christine Kenneally, The New Yorker

Further reading

• Battro, Antonio M. (2001). Half a Brain is Enough: The Story of Nico. Cambridge University Press. ISBN 0-521-78307-0. 
• Kenneally, Christine (July 3, 2006). "The Deepest Cut". The New Yorker: 36–42. 
• Choi, Charles Q. (March 2008). "Do You Need Only Half Your Brain?". Scientific American. 298 (3): 104. doi:10.1038/scientificamerican0308-104.