Planning and positioning
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Under most circumstances, deep brain stimulation (DBS) is performed under local anesthesia. The exception is a rare situation in which an intractable movement disorder precludes stable positioning; general anesthesia might then be used.
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The most frequent targets are (1) subthalamic nucleus (STN), (2) globus pallidus internus (GPi), and (3) ventralis intermedius (Vim) nucleus of the thalamus. STN and GPi stimulation are used for Parkinson disease that involves all three cardinal manifestations (i.e., bradykinesia, rigidity, and tremors); GPi is preferred to STN when there is a question about the patient’s mood status, given the potential depressive effect of STN stimulation. GPi stimulation is currently used for surgical treatment of dystonia. Vim stimulation is used for symptomatic treatment of tremors of Parkinson disease and essential tremors.
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Worldwide, some form of digital atlas is used for operative planning. Memorization of the coordinates of each target from the anterior commissure (AC), the posterior commissure (PC), and the mid-commissural point (the reference point) in stereotactic functional neurosurgery is unnecessary. The Schaltenbrand and Bailey atlas can be used to extract coordinates, if needed ( Table 42-1 ). All coordinates constitute a range and can change with head size, age, degree of brain atrophy, and possible anatomic brain asymmetry.
TABLE 42-1
Schaltenbrand and Bailey Atlas
Target Nucleus
Coordinates *
Corresponding Target
STN
Vertical = −4
Center of motor territory of STN
Lateral = 12
AP = −3/−4
GPi
Vertical = −5
Inferior border of motor territory of GPi, immediately superior to optic tract
Lateral = 18 from lateral ventricular wall
AP = +2
Vim
Vertical = 0 or −1
Labial commissure of Vim
Lateral = 50% of AC-PC distance but should be <12 mm of lateral ventricular wall
AP = 25%-30% of AC-PC distance anterior to posterior commissure
AC-PC = anterior commissure–posterior commissure; AP = anteroposterior; GPi = globus pallidus internus; STN = subthalamic nucleus; Vim = ventralis intermedius.
* Negative value in vertical axis = inferior; negative value in AP axis = posterior.
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If a manual method of calculation is contemplated, accurate knowledge of the mathematical/trigonometric principle of the frame used is necessary for calculation (contact the manufacturer of the particular frame used).
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Surgery is undertaken in two stages: The first involves the placement of one or more DBS electrodes, and the second consists of the placement of a DBS generator and connection to the electrodes.
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Placement of one DBS electrode on one side is shown in the following figures; in the case of bilateral electrode placement, the same steps are repeated on the other side.
