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Yücel Kanpolat, M.D., Ali Savas, M.D., Sükrü Çaglar, M.D., Cüneyt Temiz, M.D., and Serdar Akyar, M.D.
Departments of Neurosurgery and Radiology, University of Ankara, School of Medicine, Ankara, Turkey
Percutaneous bilateral cordotomy performed using conventional techniques may cause the patient to develop sleep-induced apnea due to bilateral destruction of the ventrolateral reticulospinal tract. Computerized tomography (CT)guided percutaneous cordotomy using a newly designed needle electrode system has the advantages of safe, selective, and controlled lesioning under direct visualization in the lateral spinothalamic tract. Given its low complication rate, bilateral selective cordotomy performed with CT guidance using this new needle electrode system may prove to be the treatment of choice for cancer patients with bilateral pain of the lower trunk and extremities.
The present series included five cancer patients suffering from intractable pain bilaterally in the lower trunk and extremities. All were treated with CT-guided bilateral selective cordotomy: the results demonstrate that this technique may be used effectively and safely.
Key Words * bilateral percutaneous cordotomy * cancer pain * computerized tomography guidance
Cordotomy is an effective procedure for relieving intractable pain and has been used to treat patients with unilateral pain of the lower body and lower extremities. Formerly, cordotomy was performed as an open surgical procedure. Conventional percutaneous cordotomy with x-ray visualization, a much less invasive procedure, allowed safe unilateral operations at the high cervical level. On the other hand, bilateral lesions high in the cervical spinal cord involving the anterior portion of the lateral spinothalamic tract have been associated with sleep-induced apnea due to bilateral destruction of the ventrolateral reticulospinal tract.[21,22,25,31,37]
The fibers transmitting pain from the lower part of the trunk and lower extremities are located in the posterolateral part of the lateral spinothalamic tract, which is farther from the ventrolateral reticulospinal tract than from its anteromedial part.[3,12,15,44] For this reason, bilateral destruction of the pain fibers from the lower trunk and extremities at the upper cervical level seems to be safer than destruction of fibers from the upper trunk and upper extremities.[28,35]
In the past decade, computerized tomography (CT)guided percutaneous cordotomy has been used as an effective and safe method to destroy the lateral spinothalamic tract in patients with cancer pain.[17,18,20] Computerized tomography guidance offers the advantage of superior topographical orientation in the spinothalamic tract, which supplies selective ablation of the upper or lower segments of the body. To maximize the advantages, the technique described should be performed with the newly designed radiofrequency needle electrode system.[19]
Computerized tomographyguided percutaneous bilateral selective cordotomy may prove to be the treatment of choice for patients suffering from bilateral cancer pain, because of the advantages of higher segmental selectivity and controlled ablation of neural structures at a higher cervical level under direct visualization. The present series included five patients with bilateral cancer pain in the lower trunk and extremities who were treated with CT-guided bilateral selective cordotomy. The bilateral selective cordotomy technique is described.
CLINICAL MATERIAL AND METHODS
Computerized tomographyguided cordotomy has been routinely used in our department since 1987. Between 1987 and 1996, 98 patients with intractable cancer pain were treated using CT-guided percutaneous cordotomy. Bilateral procedures were performed in five patients diagnosed with osteosarcoma, lumbar ependymoma, metastatic prostatic carcinoma, metastatic pulmonary carcinoma, and metastatic breast carcinoma, respectively. All patients had suffered from intractable bilateral pain of the lower extremities and lower trunk (Table 1). Only patients without pulmonary functional disorders were selected for bilateral cordotomy.
A special needle electrode system was used for the CT-guided procedures (KCTE Kit; Radionics, Inc., Burlington, MA).[19] For this system, 20-22 gauge, thin-wall needles with plastic hubs were designed to avoid imaging artifacts. Measurements of the spinal cord diameter were made, and the portion of the active electrode that had been inserted was adjusted accordingly. We recently began using different electrode tip diameters for bilateral and unilateral cordotomies: we use 0.4-mm open-tip electrodes for unilateral procedures and 0.25-mm diameter and 2-mm open-tip electrodes for bilateral procedures.
Placement of the needle at the C12 level can be seen in the lateral scanogram (Fig. 1). The needle is manipulated toward the anterior part of the spinal cord aided by axial CT sections, which facilitate topographical localization (Fig. 1). The target in percutaneous cordotomy is the lateral spinothalamic tract in the anterolateral part of the spinal cord at the C12 level, although the posterolateral part of the lateral spinothalamic tract should be targeted to control pain from the lower trunk and extremities, as is done in bilateral procedures.
Fig. 1. Computerized tomography scans showing the needle and electrode in their final positions located in the right (upper) and left (lower) spinothalamic tracts posterolaterally at the C12 level for lesioning.
Impedance measurements and stimulation are very important in localizing the active electrode tip in the spinal cord. General anesthesia should not be used because patients must be awake and responsive throughout the procedure to facilitate observation of their neurological functions. The final controlled lesion is made at 70 to 80°C for 60 seconds: usually two but a maximum of three lesions are made in each side in bilateral cordotomy. Bilateral staged procedures were performed at 1-week intervals for each patient.
RESULTS
Sensation in the upper trunk and extremities was preserved in all five patients, and destruction of the pain sensation in the lower trunk and extremities was obtained selectively (Table 1). Satisfactory pain control was obtained in all patients. The follow-up period ranged from 4 to 18 months (mean 7.6 months). We observed transient complications in one patient: unilateral Horner's syndrome and urinary retention. No other complications, including sleep-induced apnea, were observed.
DISCUSSION
Neurosurgical procedures represent an alternative approach to pain control in patients with malignancy in whom analgesic therapy is not effective. Neuroablative procedures have been directed toward the surgical interruption of pain fibers at various levels, from the anatomical site of the lesion to the cerebrum. Percutaneous cordotomy is known to be effective and advantageous in relieving unilateral intractable cancer pain. Therefore, percutaneous cordotomy has become a frequently performed procedure among the operative pain-relieving approaches at most centers.
Bilateral cordotomy is performed in patients with intractable cancer pain of the lower trunk and extremities with midline involvement. However, serious complications such as sleep-induced apnea after bilateral procedures with conventional techniques have restricted its application; mortality and morbidity rates associated with this procedure have been very high.[23,25,27,31,38]
Sectioning of the lateral spinothalamic tract in the anterolateral spinal cord is known as cordotomy. The name cordotomy was first used by Schüller.[40] The first cordotomy in man was performed by Martin at Spiller's instigation.[43] Cordotomy operations were originally open procedures, performed in the upper thoracic region via the posterior approach. High cervical cordotomy was first performed by Foerster[9], and anterior open cordotomy was described by Collis[7] and Cloward.[6]
A new dimension was added to the cordotomy procedure developed by Mullan, et al.[29] He implanted a radioactive strontium needle to interrupt the pain tract of the spinal cord. Difficulties in controlling the energy needed to create a lesion with radioactive material led to the development of new techniques that made use of electrical currents.[30] Electrolytic lesions made by unipolar anodal electrodes were also found insufficient to create well-defined, controlled lesions. Given these difficulties, Rosomoff and coworkers[36] suggested making thermal lesions with a variety of radiofrequency needle electrode systems. Since then, techniques involving radiofrequency thermal lesioning have been the standard in the performance of percutaneous cordotomy. Radiofrequency generators and needle electrode systems have also allowed stimulation and measurement of the impedance of the tissues, thus enabling neurophysiological localization.[11,44]
Until the end of the 1980s, percutaneous cordotomy was conventionally performed with x-ray visualization of the cervical spine and the cord after administration of intrathecal contrast material.[2,42] Despite the use of contrast agents, x-ray visualization does not show the target area directly. Direct visualization of the target area during cordotomy has been possible only with the use of CT guidance, as described by Kanpolat and colleagues.[17,20] With the advent of this imaging technology, cordotomy has entered into the realm of stereotactic functional procedures. Computerized tomography is used to define the target area and the spinal cord segment morphologically. Neurophysiological control is obtained by using electrical stimulation and making impedance measurements; a controlled radiofrequency lesion of a specific volume is then made.
Bilateral cordotomy has opened new doors to pain alleviating procedures in the management of intractable cancer pain. On the other hand, bilateral cordotomy procedures are associated with a higher rate of complications than are unilateral procedures.[14,22,31,35,39,41] Most complications after bilateral cordotomy are due to bilateral lesioning of the anteromedial portion of the spinal cord. In his series of 100 patients undergoing bilateral percutaneous cordotomy, Rosomoff[35] reported ataxia in 34%, bladder dysfunction in 17%, paresis in 10%, hypotension in 4%, and respiratory problems in 4%. In this series, mortality due to sleep-induced apnea was 2%. Ischia, et al.,[14] reported mortality rates ranging from 0 to 9% (2% on average) in unilateral versus 11% in bilateral procedures after C12 percutaneous cordotomy. Sindou and Daher[41] reported rates as high as 50% after bilateral cordotomy. Percutaneous bilateral cordotomy using conventional techniques is thought to be a risky operation because patients may develop sleep-induced apnea caused by destruction of the ventrolateral reticulospinal tract bilaterally, as observed after clinical and experimental studies.[3,4,12,21,22,31,32,33,37] The most critical area involving the reticulospinal tract in this region is located 3 to 5.5 mm in depth from the surface of the spinal cord.[3]
Although bilateral cordotomy is considered dangerous, even unilateral destruction of the reticulospinal tract may cause respiratory problems in patients with severe pulmonary dysfunction. For this reason, Mullan[28] proposed that unilateral cordotomy not be performed in patients with a blood PO2 level of less than 70 mm Hg.
Segmental localization of the pain fibers in the lateral spinothalamic tract was described by Walker,[45] and further clinical observations confirmed this segmentation.[5,10,13,33,34,44,46] The anterolateral sensory system has a somatotropic relationship with fibers from higher levels, which laminate medially and ventrally. The topographic representation within the pain tracts usually places the sacral segments most posterolaterally, with the segments lying more ventromedially as the cord is ascended, that is, the cervical segments are situated more medially and anteriorly.[15,44,45] The segments involving pain fibers from the chest and arm are located proximally to the reticulospinal tract. The proximity of these two areas is the source of mortality and morbidity after cordotomy performed to obtain analgesia in the chest and arms.[12,31,37]
An anterior approach to percutaneous transdiscal lower cervical cordotomy at the C45 and C56 levels was described by Lin, et al.,[26] as advantageous over the high cervical technique to avoid the possible complication of a disturbing involuntary respiration. Although the technique described seems to be safer than the lateral approach at the C12 level, it is obviously a more difficult percutaneous technique, and therefore cannot be performed routinely.
In stereotactic pain procedures, the depth of the inserted portion of the active electrode can be calibrated with CT according to the measured diameters of the spinal cord.[16] Additionally, under CT guidance, the needle electrode can be accurately directed into the lateral spinothalamic tract. Thin electrode tips, as described in the Clinical Material and Methods section, and CT guidance are essential components for selective lesioning of the lateral spinothalamic tract.[20]
The ability to create selective lesions with the help of CT guidance has allowed us to perform bilateral selective cordotomy safely and effectively. It is possible to control somatic pain from the lower part of the trunk and legs by making bilateral lesions in this region.
Lahuerta and coworkers[23,24] performed postmortem examinations on patients who had undergone cordotomy. According to their results, the risk of complications seemed to increase when a lesion covering more than 20% of the cord was made.[23] Their study indicated that the most important variable in the success or failure of cordotomy was the use of x-ray guidance with cordotomy. The reason for the complications and the ineffectiveness of pain control after x-rayguided cordotomy was the mislocalization of the lesions. Better results can be obtained with CT guidance and selective lesioning using narrower electrode tips. Therefore, we designed new electrodes with a 0.25-mm diameter and 2-mm open tip; these are more compatible with CT. Brihaye, et al.,[5] and White and Sweet[46] have stated that small lesions may lead to early pain recurrence. On the other hand, CT-guided cordotomy can be repeated safely if pain recurs; for this reason, pain recurrence is not an important problem in light of the potential complications. Additionally, Amano, et al.,[1] reported good results after bilateral cordotomies performed with bipolar concentric thin electrodes.
Because of the small number of cases in our series our data are insufficient to prove that CT-guided bilateral percutaneous selective cordotomy is the most effective treatment. Selective control of bilateral pain was achieved in all patients. Acceptable transient complications were observed, but sleep-induced apnea was not seen.
Bilateral selective cordotomy does not appear to be a safe procedure for the treatment of bilateral pain in the chest and arms. Fenstermaker, et al.,[8] recommended a CT-guided anterior approach at the C56 level for one side, and a lateral approach at the C12 level for the other side. In our opinion, this treatment protocol is preferable in such cases.
Midline myelotomy and central cord lesions (extralemniscal myelotomy) are recognized as effective ways to control intractable pain. We propose performing extralemniscal myelotomy in cases with visceral pain and bilateral cordotomy in cases with predominantly somatic bilateral pain.
In conclusion, bilateral cordotomy under CT guidance may be the technique of choice for selective control of cancer pain located bilaterally in the lower trunk and extremities. It has a low complication rate and offers selective, segmental destruction of the spinothalamic tract. With the use of recently designed needle electrodes, very small and well-defined lesions can be made with great accuracy. On the other hand, this technique should not be used for bilateral pain located in the upper trunk and upper extremities; in such cases, lesions must be made in the anterolateral parts of the lateral spinothalamic tract, and this may cause destruction of the reticulospinal tracts bilaterally.
Acknowledgment
We express our appreciation to Ms. Helen Stevens for editing this manuscript.
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Manuscript received November 22, 1996.
Accepted in final form December 18, 1996.
This study was presented at the XIIth Congress of the European Society for Stereotactic and Functional Neurosurgery, Milan, 1996.
Address reprint requests to: Yücel Kanpolat, M.D., Inkilap Sk. 24/2, Kizilay 06650 Ankara, Turkey.
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