Electrical brain mapping and epilepsy surgery

Epilepsy is one of the most common neurologic diseases in the world and is present in 4% 
of the world's population. The majority 
of patients with epilepsy can be managed medically. Intracranial surgery involves inherent 
risks; thus, surgery is only indicated if the benefits outweigh the risks of uncontrolled
 seizures. If surgery is indicated, the patient must undergo a pre-surgical evaluation that involves an extensive medical history focusing on
 seizure activity, type, frequency, and duration. In addition a physical exam must be performed to ensure 
there are no alternative causes for the seizures. The patient is considered a candidate for surgery for a variety of reasons such as inadequate response to medications; inability to tolerate medications due to side effects; seizures that significantly affect quality of life; seizures caused by a lesion such as scar tissue, brain tumor,arteriovenous malformation, or birth defect; partial seizures that always start in one area of the brain; and seizure discharges that spread to the whole brain (secondary generalization). 

iStock_000017465619XSmall.jpgOnce the patient meets the criteria for surgery, electrical brain mapping or electrocorticography is done to provide the surgeon with the necessary information about the brain
 to safely and accurately perform the surgery. Brain mapping is performed to localize the seizure focus, the area of the brain where the seizures begin. In addition, brain mapping identifies significant structures in the brain so the seizure focus may be removed without injuring vital brain structures relating to speech, comprehension, sight, movement, sensation, etc. Brain mapping is essential 
to determine whether the surgery is possible and the potential dangers to the surrounding 
brain regions.

Brain mapping determines the function of a particular area by providing direct stimulation via a current applied to a small area of the brain’s surface. Initially, the physician applies the lowest current and gradually the current is increased until a preset maximum is reached or a significant response is seen. The current interferes with how that area normally functions, but once the current is stopped that area of the brain resumes its usual activity. For example, if a current causes the patient to stop speaking, or to speak unclearly or incoherently, then that area is likely essential for language function. Once the function of an area is identified, a new location in that region is chosen and the physician starts over with the lowest current. Thus, a map is created that illustrates individual functions of different brain areas.

Electrode mapping can be performed in two ways: in a two-stage procedure (the most common way) or directly during the surgery itself. Generally, the current utilized is neither painful nor felt by the patient. However, an electrode occasionally makes contact with the membranes surrounding the brain and at these locations, the patient may experience pain or a tingling sensation when the current is applied. These contacts are easily identified and avoided because physicians always start at a low current.

In the two stage procedure, the surgeon creates an opening in the cranium that exposes the surface of the brain. Electrodes (small electrical contacts) are placed, the scalp is closed, and the patient is then closely monitored in a hospital bed. The electrodes then record the patient’s seizures identifying the seizure focus and map the areas of the brain under electrodes. The two stage procedure utilizes extra-operative brain mapping because it happens outside of an operating room. The patient is always awake, conscious, and able to fully participate during the mapping. The second stage of the procedure is the surgery itself, which removes the abnormal brain tissue using the information gathered from the electrical recordings and brain mapping.

Electrical brain mapping can also be performed during any surgery that exposes part of the brain. Therefore, it is an intraoperative procedure because it occurs during an operation. The surgeon tests locations on the brain’s surface using small electrical probes to create a map of functions. Even if the patient is under anesthesia, areas involved with movement can still be identified electrically; however, the patient must actively participate to map areas involving language, sensation, or vision. The patient is awakened from anesthesia and is given the necessary medications to eliminate pain. Intraoperative mapping is generally done when prior extraoperative mapping discovered important functions adjacent to the area targeted for removal.

Every neurosurgical procedure involves risks such as infection, bleeding, and cerebral edema (accumulation of water in the brain). The major risk for this procedure, specifically for individuals with epilepsy, is that a seizure may be triggered because mapped areas are in close proximity to where the seizures usually begin. Applying electrical currents to areas near the seizure focus can set off a seizure so physicians must closely monitor the patient’s brainwaves during the stimulation. If electrical discharges are noted that could evolve into a seizure, the stimulation is immediately stopped. If a patient suffers from a seizure, the mapping is stopped until the patient fully recovers. If the area being mapped is very sensitive, the patient is often given a powerful anti-seizure medication before receiving any further electrical stimulation.

If the surgeon collects incorrect data during electrical brain mapping and/or excises excessive brain tissue during surgery, the patient may be left with permanent neurological impairment. It is in these scenarios, among others, that a medical malpractice claim could arise.