There are several available surgical methods. In the most common method, implantation of the brain electrode is performed with the patient awake for part of the procedure, using only local anesthetic and occasional sedation. The basic surgical method is called stereotaxis (stereotactical or functional neurosurgery), a method used for approaching deep brain targets through a small skull opening. For stereotactic neurosurgery, a rigid frame is attached to the patient's head just before surgery, after the skin is anesthetized with local anesthetic. A brain imaging study (MRI or CT) is obtained with a frame in place. The images of the brain and frame are used to calculate the position of the desired brain target and guide instruments to that target with minimal trauma to the brain. After the frame placement, MRI/CT is obtained, and calculation of appropriate coordinates, the patient is taken to the operating room. At that point, an intravenous sedative is given and the stereotactic frame is fixed to the operating table. A patch of hair on top of the head is shaved (usually not the entire head), and the scalp is washed. After giving local anesthetics to the scalp, an incision is made on the top of the head behind the hairline and a small opening (about the size of a nickel) is made in the skull. At this point, all intravenous sedatives and turned off so that the patient becomes fully awake.
To maximize the precision of surgery, many centers employ a "mapping" procedure in which fine recording microelectrodes are used to record brain cell activity in the region of the intended target to confirm correct placement and adjust location if necessary. The brain mapping does not cause pain or sensation for the patients, but the patient must be calm and cooperative during the recording. The neuronal electrical activity is played on an audio monitor to that the entire surgical team can hear the signals and assess their pattern. The mapping takes from 30 minutes to 2 hours for each side of the brain depending on the individual patient. In addition, the neurological status, including vision, speech and strength is monitored frequently by the surgeon or the neurologist present.
When the correct target site is confirmed, the permanent DBS electrode is inserted and tested for about 20 minutes. The testing does not focus on relief of parkinsonian symptoms (as this can take several hours or days), but rather on presence of unwanted side effects, which tend to happen immediately. For this testing, the neurosurgeon will deliberately turn the device up to a higher intensity that used in clinical practice, in order to produce stimulation-induced side effects (tingling in arms or legs, a pulling sensation in face, tongue or arms, slurred speech or flashing lights). These sensations may be perceived as strange but are not painful.
Once the permanent DBS electrode is inserted and tested, intravenous sedation is resumed to make the patient asleep. Then the electrode is anchored securely to the skull with a plastic cap, and the scalp is closed with sutures. The stereotactic frame is removed and then the patient is placed under general anesthesia to be completely asleep for the placement of the pulse generator (battery) in the chest and for tunneling of the connector wire between the brain electrode and the pulse generator unit. This part takes approximately 45 minutes.
Certain surgical centers, such as at the University of California San Francisco (UCSF), have been investigating an alternative method for DBS electrode placement, in which the surgery is performed entirely within a high resolution MRI scanner. This method is being used under an investigational protocol, and so far, accuracy and side effect profile are very similar that to the standard technique. One advantage is that patients may be under general anesthesia for the entire implantation procedure, since no physiological testing is required.
Most patients with Parkinson’s disease affecting both sides of the body will require usually both sides of the brain to be implanted. Whether to implant both sides simultaneously or staged at two different time points depends on the specific patient and surgical center.