Percutaneous cordotomy is routinely performed using an RF system consisting of a generator, specially designed needles, and electrodes. The diameter and length of the uninsulated tip of the electrode are critical, because the lesion size is directly related to these parameters. The author uses an electrode kit (KCTE Kanpolat CT Electrode Kit, Radionics, Inc., Burlington, MA) with 20-gauge, thin-walled needles and plastic hubs designed to avoid imaging artifact problems. Demarcations on the cannula indicate the depth of insertion (Fig. 1A). The kit also includes two open-tip thermocouple electrodes with 2-mm tips and diameters of 0.30 mm and 0.40 mm (one straight-tip electrode and one curved tip). The smaller-caliber electrode (0.30 mm) is usually used for bilateral cordotomy, whereas the larger electrode is preferred for unilateral cordotomy .
The patient should have been fasting for 5 hours preoperatively. In CT-guided PC, contrast material should be administered into the subarachnoid space of the spinal cord by lumbar puncture (7-8 ml of 240 mg/l Iohexol) 20 to 30 minutes before the operation. If lumbar puncture cannot be tolerated, contrast material (5 ml Iohexol) is injected at the C1-C2 level. The patient is placed in the supine position, and the upper cervical spine must be kept in a horizontal position, particularly for X-ray-guided cordotomy (Fig. 1A, B). In conventional lateral and anterior cordotomy, the head is flexed and fixed. In CT-guided cordotomy, the procedure is performed in the CT unit with the patient in the supine position. The head is placed on the head holder, flexed and fixed with a fixation band. Local anesthesia is usually adequate, but neuroleptic anesthesia may be used if necessary. General anesthesia is used by some surgeons , although rarely, but is not recommended by the author because of the need for communication with the patient during the procedure.
The electrode system is placed on the anterolateral aspect of the an-terolateral spinal cord with the assistance of an imaging method (Fig. 2, Fig. 3). Computed tomography shows the morphology of the spinal cord segment directly, whereas X-ray allows only indirect visualization of the spinal cord without demonstration of the relationship between the spinal cord and the needle electrode.
In conventional C1-C2 lateral cordotomy, the needle is inserted perpendicularly, 1 cm below and behind the mastoid process after deep local anesthetic infiltration (Fig. 1A, B). The local anesthetic needle is used as a guide needle before the initial puncture if an X-ray or CT image is taken. As a safety precaution the author uses a cannula (Kanpolat cannula, Radionics) with demarcations demonstrating the amount penetrated.
In CT-guided cordotomy, the skin-dura distance and needle direction must be monitored. The needle is then placed 1 to 2 mm anterior to the
Figure 4 Incomplete insertion of the electrode.
dentate ligament. As lateral puncturing of the dura usually causes pain, local anesthetic infiltration is recommended. The needle position is seen at every step of manipulation on lateral scanogram and axial CT scans using a 1-mm slice thickness (Figs. 2, 3). Multiple maneuvers under CT guidance may be needed to fix the needle in this position. The active electrode is then inserted into the cannula using one insertion. The location of the electrode in the spinal cord, as well as displacement or rotation of the spinal cord, can be visualized (Figs. 1C, D; 4, 5).
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