What Are the Risks of Epilepsy Surgery?

Epilepsy surgery is a neurosurgical procedure to prevent or reduce the occurrence of epileptic seizures. Epilepsy surgery involves removal or surgical alteration of the part of the brain which is the focal point for onset of seizures.

Epileptic seizures are caused by sudden bursts of abnormal electrical activity in certain brain cells, which may spread to other parts of the brain. Epilepsy surgeries are performed to remove the brain tissue where these electrical signals originate, or disrupt the pathways by which they are transmitted.

Surgical procedures vary depending on the type of epilepsy syndrome and the focal point of seizures. A team composed of a neurosurgeon, neurologist, neuropsychologist, neuroradiologist and anesthesiologist are involved in the evaluation of a patient and performance of an epilepsy surgery. 

Certain minimally invasive procedures may be performed as outpatient procedures or with short hospital stays. Invasive epilepsy surgeries require general anesthesia and involve varying periods of hospitalization, depending on the type of surgery.

Preparation

An accurate diagnosis of the exact seizure focus area is essential for a successful epilepsy surgery. Prior to the surgery, the patient undergoes several tests which may include:

• Blood and urine tests to assess medical fitness for surgery
• Imaging tests such as:
  • Skull radiography
  • CT scan
  • MRI test
  • PET scan
  • Single-photon emission tomography (SPECT)
  • Magnetoencephalography/magnetic source imaging (MEG/MSI)
• Individually tailored neuropsychological testing to assess cognitive functions
• Intracarotid amobarbital (Wada) test to determine which brain hemisphere contains language and memory function
• Electroencephalography (EEG) and long-term video EEG (VEEG) monitoring to obtain data on frequency of seizures and seizure foci, in case there are more than one.

Invasive procedures

All invasive procedures are performed with the patient under general anesthesia.

Prior to the procedure

• The patient is required to
  • Avoid eating and drinking for eight hours
  • Check with the surgeon before taking any regular medications
  • Inform the surgeon of any allergies
• The doctor may
  • Reduce or stop antiepileptic drugs.
  • Administer antibiotics.
• The patient’s hair on the operative area is shaved and the skin sterilized.

During the procedure,

• The patient lies on their back or turned to one side depending on the type of surgical procedure.
• The anesthetic team administers anesthesia and monitors the patient’s vital functions throughout the procedure and during recovery.

The surgeon

• Makes an incision in the scalp and retracts the scalp
• Cuts out a flap of bone in the skull in a procedure known as craniotomy.
• Opens and retracts the brain’s membrane (dura) to access the brain tissue.
• Performs the required surgical procedure.
• Closes the dura, fixes the flap of bone using surgical glue and sutures the incision close.

In some procedures which can be performed with a smaller opening, the surgeon drills a burr hole in the skull and closes it with sutures in the scalp.

The patient is weaned off anesthesia and monitored for a few hours in the recovery room.

Invasive intracranial monitoring

invasive intracranial monitoring known as electrocorticography (ECOG) may be performed if noninvasive evaluation fails to find a conclusive diagnosis of seizure focus. The surgeon implants electrodes in the brain, guided by continuous X-ray (fluoroscopy).

The electrodes are connected with wires to an EEG device which maps and records seizure activities. The patient may be monitored for two to seven days. Surgery or other therapeutic procedures may follow based on the diagnosis.

Three types of electrodes are used for intracranial monitoring:

• Strip electrodes: Strip electrodes are strips of small metallic disks sheathed in silicon. The surgeon inserts the electrodes through a burr hole and places them on the surface of the brain. The leads from the electrodes are connected to an EEG device.
• Grid electrodes: Grid electrodes are arrays of electrodes which form a grid. Grid electrodes require a craniotomy and the surgeon sutures them to the dura.
• Depth electrodes: Depth electrodes can be inserted through a burr hole and are placed in deep parts of the brain, typically the amygdala or the hippocampus.

Neurostimulation procedures

Neurostimulation procedures involve implantation of electrodes connected to a battery-operated electrical stimulation device, which is also implanted under a flap of skin, typically in the upper chest. The neurostimulator delivers small electric impulses that interrupt electrical communication in the brain and prevent seizures.

The types of neurostimulation include:

• Vagus nerve stimulation (VNS): The electrodes are implanted in the neck adjacent to the vagus nerve and the neurostimulator is implanted in the top of the chest. The wires connecting them are tunneled under the skin.
• Responsive neurostimulation device (RNS): The electrodes are implanted on the surface of the brain’s seizure focus region, and the neurostimulator is implanted under the scalp.
• Deep brain stimulation (DBS): The electrodes are implanted in the hippocampus or amygdala, and the stimulator is implanted in the upper chest.

Invasive surgeries

Invasive epilepsy surgeries involve removal of brain tissue or structural alteration of brain include the following:

• Focal resection: Removal of brain tissue from the largest part of the brain known as cerebrum, consisting of two halves (hemispheres). Each hemisphere contains four sections; frontal, temporal, parietal and occipital lobes. Focal resection may be:
• Anteromedial temporal resection (AMTR): Removal of brain tissue from the anterior temporal lobe, the most common epilepsy origin point.
• Extratemporal resection: Removal of brain tissue from any of the three lobes other than the temporal lobe.
• Lesionectomy: Removal of lesions in the brain tissue.
• Corpus callosotomy: Severing of the corpus callosum, a band of nerve fibers that connects the two cerebral hemispheres.
• Functional hemispherectomy: Removal of a minimal amount of brain tissue from one hemisphere as necessary, and disconnection of its communication with the rest of the brain. In a hemispherectomy an entire hemisphere of the brain is removed.
• Multiple subpial transection (MST): Fine, shallow cuts in the brain tissue to interrupt flow of seizure impulses in parts of the brain which have critical functions such as speech, memory, vision and movement, and are not safe to remove.

Minimally invasive procedures

Some newly developed procedures are minimally invasive, and may be performed as an outpatient procedure or with a very short hospital stay. These include:

• Stereotactic radiosurgery: A procedure which delivers high doses of precisely focused radiation to destroy brain tissue in the seizure focus area.
• Laser interstitial thermal therapy (LITT): A procedure using laser to eliminate seizure-causing brain tissue.

Recovery time depends on the type of surgery performed. With minimally invasive procedures the patient usually can resume normal activities within a day or two. Invasive surgeries may require hospitalization of up to a week, and most patients resume normal activity in six to eight weeks.

Patients must continue taking antiepileptic drugs after surgery, though the doctor may reduce the dosage gradually if the patients remain seizure-free. It may take months for cognitive functions like attention span, memory and thinking to return to normal. Some patients may need therapy if they develop any neurofunctional deficits.

All patients may not find relief from seizures after an epilepsy surgery. Surgeries have been found to be effective in preventing seizures in approximately 60% of the patients. Some patients continue to have seizures, but with less frequency and intensity. Some may have no worthwhile benefit.

Epilepsy surgery is a major procedure involving a vital organ and has risks that any major surgery poses. Risks vary with individuals depending on the area of surgery and underlying conditions. Some difficulties from the surgery are temporary and resolve gradually.

One of the primary risks is lack of relief from seizures. Other risks include:

• Anesthetic side effects such as
  • Headache
  • Nausea and vomiting
  • Confusion
  • Reaction to the anesthetic
• Surgical risks such as
  • Hemorrhage
  • Wound infection
  • Aseptic or bacterial meningitis
  • Infection in the operative area
  • Injury to brain tissue, blood vessels or nerves
  • Leakage of cerebrospinal fluid (CSF)

In addition, procedure-specific complications include the following:

• Strip electrode implantation
  • Cortical contusion
  • Cerebral edema
  • Brain abscess and collection of pus under the dura (subdural empyema)
  • Misplacement of displacement of electrodes
• Grid electrode implantation
  • Transient neurologic deficit
  • Hematoma
  • Cerebral edema with elevated intracranial pressure
  • Tissue death (infarction)
• Depth electrode implantation
  • Intracerebral bleeding (intraparenchymal hemorrhage)
  • Bleeding in the space around the brain (subarachnoid hemorrhage)
  • Arterial spasm
  • Misplacement or displacement of electrodes
  • Rarely, permanent neurological deficit
• Focal resection
  • Hemiparesis (weakness in one whole side of the body)
  • Visual field deficits
  • Ocular motor paresis (loss of eye and eyelid movements due to ocular nerve damage)
  • Speech and memory problems
• Corpus callosotomy
  • Hydrocephalus (accumulation of cerebrospinal fluid)
  • Frontal lobe cerebral edema
  • Excessive blood loss
  • Air embolism (blood vessel blockage by a gas or air bubble)
  • Venous infarction (tissue death due to obstruction in veins)
• Functional hemispherectomy
  • Ventriculitis (inflammation of the brain’s ventricles)
  • Hydrocephalus
  • Postoperative hemorrhage
  • Stroke
  • Coma
• Complications are rare with minimally invasive procedures, but stereotactic radiosurgery and laser interstitial thermal therapies carry risks such as:
  • Tissue and nerve damage
  • Cerebral bleeding or edema