Functional Brain Mapping for Brain Tumors and Epilepsy Surgery

Introduction:

Resection (removal) of brain tumors, and removal of areas of the brain which are generating seizure activity in medically intractable epilepsy (cortical resections), are delicate operations that often require identification of essential areas of the brain. Neurosurgeons at the University of Washington in Seattle use a technique called Functional Brain Mapping that helps them identify critical functional regions of the brain -- motor areas, which control movement; somatosensory areas, which control sensation; and expressive and receptive language areas, which control both talking and understanding communication. By mapping the brain, the neurosurgeon can find a balance between removing tumors and areas of seizure activity, and minimizing damage to areas affecting patient quality of life.

Overview and Characteristics of Brain Tumors and/or Epilepsy:

Symptoms -
The symptoms of brain tumors depend on the location of the tumor. Common symptoms include headaches, confusion, weakness, seizures, language troubles, double vision. However, tumors can be very large and cause no symptoms, or very small and cause major problems.

Because injuries to the brain are manifested by injury location, rather than injury type, strokes, head injuries, infections and other insults to the brain can have similar symptoms to brain tumors.

Types -
Any condition that requires entry into the brain or resection of part of the brain may be aided by functional mapping. This is determined by the proximity of the surgery to areas of the brain that are critical for function. These conditions include surgery for brain tumors of all types and surgery for medically refractory epilepsy.

Incidence and Risk Factors -
There are no common risk factors for brain tumors. There are rare inherited (familial) syndromes that can be associated with brain tumors. Tumors in the brain are not known to be associated with foods, chemicals, cell phone use, or exposure to electrical wires. Primary brain tumors (those that start in the brain) occur in about 6 out of every 10,000 people in the United States each year. Secondary (metastatic) brain tumors (those that spread to the brain from other tumors) occur in about 20% of those with cancer. Some of these tumors have known associations, such as lung cancer and smoking.

On the other hand, epilepsy can be due to any type of brain injury (tumor, infection, stroke, birth injury, high childhood fever, head trauma) and can run in families.

Diagnosis -
The most important tests for brain tumors are MRI and/or CT scans. These show where the tumor is located, the size of the tumor, and often give hints about the type of tumor and its degree of malignancy.

Figure 1: The “chemical signature” of tumor can be quite different from normal brain, stroke or infection. To view this, MRI spectroscopy is used to make a “chemical map” of the brain. These figures show an example of MRI multi-voxel spectroscopy demonstrating a brain tumor in the brainstem and corpus callosum.

Figure 2: Blood flow often increases in brain tumors. MRI perfusion studies can demonstrate this phenomenon. This Figure shows the increased blood flow in the tumor shown in Figure 1.

All cases are presented at the multi-disciplinary Neuro-Oncology Tumor Board for management decisions (Figure 3 - to right). This team includes neurologists, neurosurgeons, neuropathologists, neuroradiologists, radiation oncologists, brain tumor researchers, nurses and social workers.

For epilepsy surgery, there is a standard pre-operative workup. First, the patient's seizures must be incurable (intractable) with medications. The patient is then admitted for scalp EEG monitoring to localize the area of seizure onset. When scalp recordings do not clearly delineate the epileptic focus, electrodes must be placed intracranially, over the surface of the brain. An MRI scan is obtained to look for lesions that could be causing the epilepsy. Preoperative neuropsychological testing helps the epilepsy team localize the seizure onset region. All cases are discussed at the Regional Epilepsy Center's epilepsy surgery conference, where a multi-disciplinary team makes management decisions. This team includes neurologists, neurosurgeons, neuropsychologists, occupational therapists, social workers, nurses and epilepsy researchers.

For some patients with tumors or epilepsy, a preoperative "Wada test" is performed. This involves angiography with administration of sodium amobarbital into each carotid artery to put each half of the brain to sleep in order to test the "awake" half for language and/or memory skills. This tells the team which side of the brain is important for these functions.

Management and Treatment:

Brain tumors require a "tissue diagnosis" prior to any treatment. Without a diagnosis, ineffective therapies might be used. Sometimes chemotherapy is used following surgery. Most epilepsy can be treated successfully with medications. It is only untreatable cases (medically intractable) where surgery is considered a viable option. Unfortunately, exercise does not help with either of these conditions.

Possible Benefits of Surgery -
For brain tumors, surgery has three goals: obtain a diagnosis, decrease the tumor "mass effects" on the brain (stop the pressure effects of the tumor mass within the skull) and remove as much of the tumor as can be done safely. For some brain tumors, surgery is curative. Others require additional therapies after surgery to address invading tumor cells. Even for the most malignant brain tumors, surgery is the first step toward aggressive therapy.

For epilepsy surgery the single goal is to stop the seizures. The success rate depends on the location of the seizures and the presence (or absence) of a structural brain lesion.

Surgery:

Who should consider surgery?
Brain tumors almost always require surgery for diagnosis and tumor removal (resection). When a tumor is inoperable, a computer-directed (stereotactic) biopsy is performed to obtain a diagnosis. When operable, surgery is usually the best choice. When epilepsy is medically intractable, the patient is a candidate for a preoperative workup. Surgery is recommended when the epilepsy arises from only one place and that place can safely be removed.

What kinds of surgery are recommended?
Brain tumors usually require surgery. This may be a biopsy to obtain a definitive diagnosis, or a larger operation to remove the tumor. The surgical treatment of epilepsy is undertaken to remove the area of the brain where the seizures begin.

What are the logistics of surgery?
The patient arrives the day of surgery. Most patients have stickers applied to their head followed by an MRI scan. This MRI is used to train an intra-operative navigational system. The surgeon uses three ways of "looking" at the brain: the "Stealth" navigational system, intra-operative ultrasound and the surgeon's vision augmented with magnification.

Figure 4: Intra-operative ultrasound is used in conjunction with the operating microscope and the MRI-based intra-operative navigation system. The image on the left shows the ultrasound being used to delineate the tumor prior to opening the coverings of the brain (the dura). The image on the right shows a combination ultrasound and vascular Doppler image of the tumor. This enables visualization of the tumor and the surrounding blood vessels.

From the MRI scanner, the patient is transferred to the pre-operative area, where IV's are started and the patient talks with the operating room nurse and anesthesiologist. From there, the patient is taken into the operating room.

The patient is then placed under anesthesia. Motor mapping and sensory mapping can be performed with the patient under general anesthesia, while language mapping requires the patient to be awake during the mapping. For awake mapping, the patient is under anesthesia (asleep) except during the mapping part of the procedure.

Sensory mapping is performed by electrically stimulating a nerve in the arm or leg and then recording the brain's response. This is called somatosensory evoked potentials or SSEP's. (Figure 5 - to right)

Motor mapping is performed by electrically stimulating the brain directly in order to elicit patient movement. Although the patient may be under general anesthesia, movements can still be evoked.

Figure 6: The areas of the brain essential for movement (motor cortex; shaded area in left photo) and sensation (sensory cortex; shaded area in right photo) are on the opposite side of the body can be identified with electrical stimulation of the surface of the brain.

Language mapping commences after all anesthetic is stopped and the patient is fully awake. Why isn't this painful? Only the scalp has sensation. The skull and the brain have no sensation at all. After the patient is asleep, the surgeon injects local anesthetic (just like at the dentist) into the scalp. The patient is asleep during this part of the procedure, so this is not painful. Once the patient is fully awake, the surgeon electrically stimulates the patient's brain, the patient names objects presented on slides. When the area that is essential for language is stimulated, the patient is unable to name the presented object.

Figure 7: Recording the electrical activity from the surface of the brain (electrocorticography) can be used to identify epileptic areas (left photo) and to determine the current needed for electrical stimulation mapping (right photo).

Once the surgeon knows where the "bad stuff" is located (the tumor or the epileptic brain region) and where the "good stuff" (important functional brain) is located, the surgeon can formulate a strategy which maximizes patient safety and resection. Figure 8: This photograph of the brain during surgery shows the findings from mapping sensation, movement and language. The area of the brain important for sensation is underneath numbers 1, 2, 3, 10, 11.The brain region essential for movement lies beneath numbers 4, 5, 7, 8, 9. Essential language cortex is located beneath B and C.

Figure 9: Temporal lobe language sites (shaded area in left photo) are important for understanding language. Frontal lobe language sites (shaded area in right photo) are important for language expression.

Surgery typically lasts 3-6 hours. Following surgery, the patient is transferred to the recovery room and the surgeon speaks with family and friends in the surgery waiting room. The patient is moved to the intensive care unit (ICU). If all is going as expected, the patient moves to the regular floor the next day. The typical hospital stay is 3-4 days.

The patient and family return to the surgeon's outpatient clinic 6-10 days after surgery. During this visit, staples are removed from the incision and pathology is discussed. It is important to know that pathology results (e.g. type of tumor) take 5-7 days. When postoperative therapies are recommended by the multi-disciplinary team (the Neuro-Oncology Tumor Board or the Epilepsy Team), these are conveyed to the patient and family. Additional appointments are made if the other physicians needed for care are unavailable during this clinic visit.

Our goal is to provide safe, multi-disciplinary, compassionate state-of-the-art care. Each physician member of these specialized, multi-disciplinary teams is also involved in research so that in the future, care will be better than it is today.

Effectiveness of Surgery -
The prognosis for brain tumors depends on the type of tumor (name and grade of malignancy). For some tumors, surgery is curative. For others, it is part of a multi-step treatment program.

Following epilepsy surgery, patients who are seizure-free begin getting off their anti-convulsants six months after surgery. Patients who remain seizure-free at two years rarely have recurrent seizures.

Risks of Surgery -
Although the risks are small, brain surgery carries serious risks. The precise risks depend on the patient, the procedure planned and the location of the tumor or epileptic brain to be removed. General risks include bleeding, infection, anesthesia, heart problems, lung problems, stroke, coma and injury to brain near the surgery.

Risks of not having Surgery -
Brain tumors grow. This growth can lead to worsened symptoms and can make an operable tumor unsafe for surgery.

Epilepsy surgery can stop medically intractable seizures. Without surgery, the seizures continue to disrupt and limit the patient's life.

Urgency -
Surgery for brain tumors may be urgent or elective (can be planned when it is convenient). This depends on the symptoms and tumor size. Epilepsy surgery is always elective.

Managing Risk -
Although rare, all surgical and postoperative problems are taken very seriously. Every step is taken to minimize the risks of surgery. When problems do occur, a team approach is usually used to provide optimal care. For instance, infections are managed with the University of Washington's Infectious Diseases service. The Rehabilitation Medicine service becomes involved whenever appropriate, providing speech therapy, physical therapy, occupational therapy and other services that help pateints improve the quality of their lives.

Contraindications -
Some people cannot have surgery due to unrelated medical problems. This is rare and can be investigated by the Anesthesia team at the University of Washington.

Contact Us -
Patients with brain tumors or medically intractable epilepsy can arrange a clinic appointment or multi-disciplinary team review of records and films by calling our neurosurgery nursing team, at 206-598-9469.

Introduction | Aneurysms | Brain Mapping | Case Studies | Chiari Malformation
Congenital Abnormalities | Epilepsy | Movement Disorders | Pain and Spasticity
Pediatrics | Peripheral Nerves | Radio Surgery and Radiotherapy
Spine | Stroke and Vascular Lesions | Trauma | Tumors

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