Hemispherotomy is a rare but highly effective neurosurgical procedure performed to treat severe neurological disorders originating from one hemisphere of the brain. Unlike a hemispherectomy, which involves removing a portion of the brain, hemispherotomy disconnects the affected hemisphere from the rest of the brain to stop abnormal electrical activity. This surgery is often considered a last resort when medication fails to control severe epilepsy. But what exactly leads to the need for such an invasive intervention?

What makes this surgery unique is that it doesn’t involve the removal of large brain tissue, as in the older technique called hemispherectomy. Instead, hemispherotomy is a less invasive yet equally powerful intervention that cuts off the faulty hemisphere’s communication with the healthy side. This approach reduces surgical trauma while preserving the brain’s structure as much as possible.

What Is Hemispherotomy?

Before diving into the causes, it’s important to understand what hemispherotomy involves. Hemispherotomy is a functional neurosurgical procedure designed to isolate one hemisphere of the brain to prevent the spread of epileptic seizures. The goal is to retain as much brain tissue as possible while halting the seizure activity.

This surgery is most often performed in children, as their developing brains have a higher capacity for neuroplasticity meaning the healthy hemisphere can often compensate for the functions lost in the disconnected side. It is considered when seizures are frequent, drug-resistant, and cause cognitive or physical decline.

The Role of Drug Resistant Epilepsy

The most common cause that leads to a hemispherotomy is drug resistant epilepsy, also known as intractable epilepsy. This condition refers to epilepsy that does not respond to at least two appropriate anti seizure medications. When seizures continue despite pharmaceutical treatment, especially if they arise from one hemisphere, surgical options like hemispherotomy come into play.

Epileptic seizures can severely impair a child’s cognitive, emotional, and physical development. In such cases, early surgical intervention might be the only way to improve quality of life and halt further neurological decline.

Causes of Hemispherotomy

Several specific neurological disorders can affect one hemisphere of the brain to the extent that a hemispherotomy becomes necessary. Below are the primary conditions known to trigger this intervention :-

Rasmussen’s Encephalitis :- One of the leading causes of hemispherotomy is Rasmussen’s encephalitis, a rare chronic inflammatory neurological disorder. It typically affects children and leads to progressive brain damage in one hemisphere. The hallmark symptoms include continuous focal seizures, progressive weakness on one side of the body (hemiparesis), and cognitive decline.

Despite being rare, Rasmussen’s encephalitis is a major reason for early surgical intervention, as it is notoriously resistant to medical treatment. Hemispherotomy can stop the progression of seizures and prevent further brain atrophy.
Hemimegalencephaly :- Hemimegalencephaly is a congenital brain malformation where one cerebral hemisphere is abnormally large due to excessive growth of neurons and supporting cells. This condition often causes severe epilepsy that begins in infancy and doesn’t respond well to medication.

Children with hemimegalencephaly usually suffer from developmental delays, motor deficits, and seizures. Since the condition is localized to one hemisphere, a hemispherotomy may offer significant seizure control and developmental improvement over time.
Cortical Dysplasia :- Cortical dysplasia refers to abnormal development of brain cortical tissue, which can occur in one or both hemispheres. When this malformation is confined to one side, and if the seizures are particularly severe or frequent, hemispherotomy becomes a surgical option.

This condition is one of the most common causes of intractable epilepsy in children. The abnormal brain cells can generate erratic electrical signals that trigger seizures. If medications fail to manage it effectively, surgical disconnection of the affected hemisphere is considered.
Sturge Weber Syndrome :- Sturge Weber syndrome (SWS) is a rare congenital disorder marked by abnormal blood vessels in the brain and skin. It often involves one hemisphere and leads to seizures, stroke like episodes, and developmental delays.

Children with SWS may have frequent seizures originating from the hemisphere affected by the abnormal vascular growth. When these seizures become drug-resistant, a hemispherotomy may help improve seizure control and prevent further neurological damage.
Perinatal Stroke or Brain Injury :- In some cases, perinatal stroke or brain injury occurring shortly before, during, or after birth can severely damage one hemisphere. The resulting scar tissue can become a focus for recurrent seizures.

Such injuries may not always be immediately noticeable but can become evident as the child begins to miss developmental milestones. Seizures that result from early brain injury are often resistant to drug therapy, and surgical intervention may become necessary if seizures are localized to the damaged hemisphere.

When Is Hemispherotomy Recommended?

Hemispherotomy is considered only when there is a clear localization of seizure activity to one hemisphere, and when all other treatment options have failed. This decision is made after extensive diagnostic testing, including :-

MRI scans to detect structural abnormalities
Electroencephalogram (EEG) to monitor seizure activity
PET or SPECT imaging to identify metabolic issues in the brain

Multidisciplinary teams involving neurologists, neurosurgeons, psychologists, and therapists assess whether the surgery would significantly reduce seizures and improve quality of life.

Risks and Benefits of Hemispherotomy

As with any brain surgery, hemispherotomy carries certain risks such as infection, bleeding, or hydrocephalus. Patients will also experience loss of function (motor, visual) on the opposite side of the body to the disconnected hemisphere. However, in many cases especially when the brain is already significantly damaged these deficits are already present or may worsen gradually if surgery is not performed.

The primary benefit is seizure freedom or significant seizure reduction, which leads to better developmental progress and quality of life. Many children who undergo the procedure go on to live active, seizure-free lives with appropriate therapy and support.

Conclusion

Hemispherotomy is a life saving and life changing procedure for individuals suffering from severe, drug resistant epilepsy stemming from one hemisphere of the brain. While it is a drastic step, it often provides the only real hope for seizure control in cases involving conditions like Rasmussen’s encephalitis, hemimegalencephaly, cortical dysplasia, and Sturge Weber syndrome.