Ambulation is usually begun that night or in the morning, but patients are instructed to initially ambulate with assistance for fear of falling because of changes in tone that occurred immediately after surgery. These changes ironically are often secondary to improvement in the contralateral extremity. Patients are discharged the following day and are instructed to maintain their parkinsonian medications at the same doses as before. Adjustments are then made by their referring neurologist as necessary.

Postoperative brain MRI of the pallidotomy/thalamotomy site is performed 1-3 months after surgical intervention. Early in the series in order to ensure ideal placement in all patients, filming was performed approximately 1 month after surgery but we have found that imaging at 3 months after surgery is more reliable since most of the edema from the initial lesion will have disappeared by that time. With recent testing of the safety of MRI on DBS patients postoperatively, we have begun to image patients with DBS placements postoperatively to visualize electrode placement.

CONCLUSION
Imaging is a most important component to the success of this surgery, second only to patient selection. Clearly, patients in whom PD or essential tremor is not defined well before the operative procedure will not receive the operative results that have been seen at our center or other centers where this procedure is performed routinely. The pallidotomy procedure is noted to be, as mentioned above, extremely effective for the treatment of the dyskinesias induced by parkinsonian medication and also helps manage tremor, rigidity, and bradykinesia. It is not as effective in treating some of the other parkinsonian components such as akinesia, freezing episodes, and gait or postural instability. Rigidity appears to almost always be improved with this procedure.

Using more sophisticated techniques for MRI localization that limit distortion to a minimum has proven critical in our center and has significantly improved the effectiveness and the efficiency at which surgery can be performed. We believe that the imaging protocol described in this chapter provides a high degree of safety; in particular, studies performed to precisely localize the target, the adjacent major fiber tracts, and the entry point/trajectory plan can significantly reduce the risk of intracerebral hemorrhage or inadvertent entrance into the ventricular system. Indeed, although it is an older test, we measure impedance as the lesioning electrode is passed to its target and try to maintain the impedance between 400 to 600 ohms throughout its passage, suggesting continued passage through brain substance and no passage through the ventricular system or other structures. Confirmation of MRI distortion has been done via CT, but we have found that we can routinely perform ail planning using the MRI sequences discussed above. This has obviated the need for microelectrodes that were initially utilized to confirm planning but have now been noted to only confirm the expected, and therefore are an unnecessary portion of the procedure. This has been noted throughout the literature with supporters both for microelectrode-guided surgery as well as those claiming the lack of need of microelectrodes. With the planning MRI software and imaging capabilities currently available in our center, we have found that microelectrodes are no longer necessary either for lesioning or stimulation in the globus pallidus or in the Vim nucleus of the thalamus. Whether these recording techniques will be useful for sites such as the subthalamic nucleus remains to be tested.

Using sophisticated imaging, the time spent in the planning of the surgical intervention is increased, although the surgery itself can usually be done in a fairly short period of time. For example, from the time a patient enters the operating room until wound closure and transfer to the patient's room, the pallidotomy procedure can be done in 1 hour or less and the DBS procedure can be performed in 1.5 to 2 hours. We believe that using this procedure results in less discomfort and fewer problems for the patient; in addition, it may actually increase safety, particularly in patients with stimulator placement because the shortened operating room time reduces the risk of infection and safeguards the patient from the potential risks of multiple microelectrode passes during the surgical procedure, which increases the risk of intracranial bleeding and increases the total operating room time by several hours. Knowledge and use of microelectrodes is still useful, particularly in cases where the initial testing does not provide the results desired and should be prepared for ahead of time in these particular instances. In addition, such physiological monitoring using microelectrode techniques will prove invaluable when stereotactic surgeons explore other areas of the brain for surgical treatment in the future, particularly when the target is less defined than the thalamic and pallidal targets are for the current treatment of PD and essential tremor. They will prove particularly useful in the treatment of other movement disorders as well as further understanding of the electrophysiological connections within the basal ganglia and other neurosystems.