SURGERY WITHOUT SCALPEL

AT FIRST, Christine's headache, although severe, was thought to be no cause for alarm; after all, it disappeared within a day. But then Christine developed a stiff neck. Next, her headache returned, and she became disoriented—unusual symptoms for anyone, much less an eight-year-old child.

At the hospital a computed tomography (CT) scan revealed that Christine had an arteriovenous malformation (AVM) in her brain—a condition in which arteries are entangled with veins.* Without treatment, Christine could eventually have suffered a lethal stroke.

Until recent years such AVMs could be treated only with invasive brain surgery. In this procedure the surgeon pulls back the scalp and cuts through the skull. Then, he must weave through a delicate maze of nerves and brain tissue to reach the lesion. Clinical reviews reveal that during 1995, there were complications in about 12 percent of AVM operations.

Christine's parents opted for the Gamma Knife rather than the surgical knife. The name is somewhat deceiving, for the Gamma Knife is not really a knife. Rather, it is a device that fires 201 finely focused beams of radiation through the intact skull. Each beam on its own is too weak to damage the tissue it penetrates. But all 201 beams are carefully aimed to intersect and deliver a high dose of radiation at the precise location of the lesion.



The Development of Radiosurgery

The Gamma Knife was developed almost 50 years ago by neurosurgeon Lars Leksell and biophysicist Börje Larsson. Leksell discovered that a single, intense dose of irradiation could demolish deep-seated brain lesions without an incision—hence, without bleeding or risk of infection.

Leksell called his new procedure stereotactic radiosurgery. Finally, doctors had a means of treating previously inaccessible parts of the brain, without having to use a scalpel to weave crudely through a maze of delicate nerves and brain tissue. However, the application of this new procedure had to wait many years for the development of modern imaging techniques, such as the CT scan and MRI, which can tell surgeons precisely where to aim the radiation. The first Gamma Knife unit was installed in Stockholm in 1968.



The Gamma Knife has in some studies proved cost-effective, and there are significantly fewer cases of postoperation infection than with conventional neurosurgery. But how is the procedure performed?
The Four Steps of Radiosurgery

Gamma Knife radiosurgery is performed in four basic steps. First, the patient's head is fitted with a lightweight frame, which will hold the patient still during treatment. Second, a "map" of the patient's brain is made, by means of either a CT scan, magnetic resonance imaging (MRI), or an angiogram. Next, images of the brain are transferred to a computerized treatment-planning system, which isolates the target and determines its coordinates.

Finally, it is time for the treatment phase, during which the patient's head is positioned in a helmet with 201 portals through which the gamma rays are emitted. The duration of treatment? Only 15 to 45 minutes, during which the patient is mildly sedated and feels no pain.


THE FOUR STEPS OF GAMMA KNIFE RADIOSURGERY

1. Fitting the frame
Fitting the frame

2. Making images
of the brain
Making images of the brain

3. Computerized images help
with treatment planning
Making computerized images

4. Treatment phase Treatment phase

Images courtesy of Elekta Instruments, Inc., manufacturers of the Gamma Knife


When treatment is completed, the patient remains in the hospital for observation and is usually discharged by the following morning. This was so in the case of Christine, mentioned at the outset. She was treated on Thursday, released on Friday, and back in school the following Monday.
What Happens to the AVM?

Radiosurgery does not literally destroy the arteriovenous malformation. Instead, it causes cells in the lining of the vessels to multiply, thus sealing off blood flow to the problem area. As a result, in perhaps a year or two, the defective vessels are completely blocked off. Then the arteriovenous malformation shrinks and eventually is dissolved by the body.

The Gamma Knife has also been used to treat small malignant tumors that have well-defined borders as well as some metastatic tumors, which are spread to the brain from cancer in other parts of the body. In addition, it has shown promising results with trigeminal neuralgia (a painful condition that affects the facial nerve), epilepsy, Parkinson's disease, and some cases of intractable pain.

Of course, there are still some brain tumors and conditions that defy the Gamma Knife. Whether advances in neurosurgery will lead to even more effective treatments remains to be seen. In the meantime, Gamma Knife radiosurgery offers hope to many tumor patients.

* A CT scan is a cross-sectional X ray of a part of the body.