Published online before print March 7, 2002, 10.1148/radiol.2231010751
(Radiology 2002;223:574-580.)
© RSNA, 2002
MR Guidance of Sympathetic Nerve Blockade: Measurement of Vasomotor Response—Initial Experience in Seven Patients1
Daniel Y. Sze, MD, PhD and
Sean C. Mackey, MD, PhD
1 From the Division of Cardiovascular and Interventional Radiology, Department of Radiology (D.Y.S.), and Division of Pain Management, Department of Anesthesiology (S.C.M.), Stanford University Medical Center, 300 Pasteur Dr, Stanford, CA 94305. Received April 11, 2001; revision requested May 18; revision received August 24; accepted September 28. Address correspondence to D.Y.S. (e-mail: dansze@stanford.edu).
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ABSTRACT
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The authors performed sympathetic nerve blockades in seven patients with peripheral ischemia and possible autonomic dysfunction. Magnetic resonance (MR) imaging was used to guide needle placement, to monitor distribution of injected agents, and to measure increases in blood flow, which were as much as 10-fold. MR imaging can provide both procedural imaging guidance and measurement of efficacy for sympathetic nerve blocks.
© RSNA, 2002
Index terms: Anesthesia, 30.1264, 90.1266 • Blood, flow dynamics, 30.12141, 90.12941 • Magnetic resonance (MR), cine study, 30.12141, 30.12144, 90.12941, 99.12944 • Magnetic resonance (MR), guidance, 30.1264, 90.1266 • Nerves, interventional procedures, 30.1264, 90.1266 • Nerves, peripheral, 30.1264, 90.1266
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INTRODUCTION
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Regional anesthesia was originally developed to be performed with use of only anatomic landmarks for needle guidance (1,2). With improved imaging technology and with increased collaboration between disciplines, the scope of regional anesthetic applications has greatly expanded. Although fluoroscopy is accessible and well accepted, the advantages of cross-sectional imaging such as ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging can be exploited to maximize the chances for success, particularly in patients at high risk (3–5). The superior soft-tissue characterization of MR imaging can be especially useful for guidance of percutaneous procedures in deep structures, such as the retroperitoneum. This advantage of superior tissue characterization and the lack of ionizing radiation are responsible for the increasing enthusiasm for MR imaging as the preferred imaging modality for guidance of particularly challenging percutaneous procedures, including biopsies, needle localizations, and tumor ablations (6,7).
Recently, MR imaging guidance has been successfully used to perform regional nerve blocks, including blockade of the stellate, celiac, lumbar sympathetic, hypogastric, and impar ganglia (8). In addition to providing cross-sectional images at infinitely adjustable obliquities for needle guidance, MR imaging can provide direct visualization of the distribution of injected anesthetic or neurolytic agents in three dimensions and in nearly real time. MR imaging guidance has proved especially valuable when normal anatomy is distorted by tumor, scarring, or surgery (8).
With the continuing expansion of the diagnostic capabilities of MR imaging, the role of MR imaging in imaging-guided interventions will no longer be confined to providing morphologic depiction of instruments and targets but will encompass monitoring of the effects of therapeutic interventions. For instance, MR thermometry can be used to provide immediate feedback on the extent of tissue damage after percutaneous tumor ablation (7). The purpose of this study was to evaluate the capability of MR imaging to detect and quantify blood flow to affected extremities after performance of MR-guided sympathetic nerve blockade.
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Materials and Methods
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Nine procedures in 11 limbs were performed in seven consecutive patients with a variety of vascular diseases (Table 1). MR imaging-guided procedures were reviewed and approved by the hospital institutional review board, and informed consent was obtained from each patient or the parents or guardians of the three minor patients. The patients were aged 17–77 years (mean, 39.1 years). Three patients were male, four were female. Three patients, all younger than 20 years, experienced complex regional pain syndrome (CRPS) that resulted from physical injuries to the upper (n = 1) or lower (n = 2) extremities. Other vascular diseases included atherosclerotic peripheral vascular disease; thromboangiitis obliterans (Burgher disease); end-stage scleroderma; and multiple sclerosis treated with stem cell transplantation, complicated by CRPS and erythromelalgia. All patients had undergone previous therapies for their conditions, including two who had undergone fluoroscopy-guided sympathetic nerve blocks and one who had undergone surgical sympathectomy 3 years previously.
Procedures were performed with an open-configuration 0.5-T MR imaging system (Signa SP; GE Medical Systems, Milwaukee, Wis). The six patients who underwent lumbar sympathetic blockade were placed prone on the procedure table and fitted with a large flexible surface coil. Self-adhesive liquid crystal thermometers with temperature range of 34.0°C–40.5°C (Crystaline II; Sharn, Tampa, Fla) were affixed to bilateral plantar and dorsal surfaces of the feet and medial and lateral surfaces of the ankles. Small doses of sedatives (fentanyl citrate, 25–50 µg; midazolam hydrochloride, 0.5–1.0 mg) were administered via peripheral intravenous catheters as needed, with total doses of 42 µg and 0.9 mg, respectively (fentanyl range, 0–125 µg; midazolam hydrochloride range, 0–3.0 mg). Cardiac rhythm, blood pressure, and pulse oximetry were continuously monitored. Ambient room temperature was kept at 20°C ± 2, and patients were offered blankets for comfort. Velocity-encoded transverse cine MR imaging (9,10) (repetition time msec/echo time msec of 20/9.1, velocity encoding of 150 cm/sec, 10-mm section thickness, two signals acquired, 256 x 128 matrix) was performed in the popliteal arteries and veins at the level of the femoral condyles. The surface coil was then repositioned to the pelvis, and cine images of the common femoral arteries and veins were obtained at the level of the femoral heads. The surface coil was then further repositioned to the torso and lumbar spine region.
Initial transverse and sagittal images of the lumbar spine region were obtained with multiplanar spoiled gradient-echo, T1- and T2-weighted fast spin-echo, and fast imaging with steady-state precession, or FISP, sequences. The optimal pulse sequence for imaging guidance of needle placement was selected (D.Y.S., S.C.M.) from these images and varied by patient. Oblique axial trajectories were mapped from the lateral aspect of the quadratus lumborum muscle, medial to the kidney and either lateral to or traversing the psoas muscle, to the anterolateral retroperitoneum posterior to the aorta or inferior vena cava at the level of L2. Image interpretation, treatment planning, and actual procedures were performed by a team of one interventional radiologist (D.Y.S.) and one anesthesiologist (S.C.M.).
After administration of approximately 3 mL of 1% lidocaine hydrochloride for local anesthesia, a 20-gauge 10-cm-long nonferromagnetic stainless steel needle (MREye; Cook, Bloomington, Ind) was advanced with repetitive single-section gradient-echo MR imaging guidance to the target site. Three milliliters of preservative-free 0.25% bupivacaine hydrochloride solution (Abbott Laboratories, Abbott Park, Ill) doped with 1:100 gadolinium-based contrast agent (Omniscan; Nycomed, Princeton, NJ) was injected after the stylet was removed. Transverse and sagittal T1-weighted fast spin-echo and fast imaging with steady-state precession sequences were repeated to document the distribution of this test injection of anesthetic agent.
After confirmation of needle location and distribution of bupivacaine hydrochloride, a total of 15 mL of bupivacaine hydrochloride solution (37.5 mg) was injected, and imaging was repeated. Distribution of the injected agent in craniocaudal, anteroposterior, and lateral directions was evaluated (D.Y.S., S.C.M.) on these images to confirm saturation of the expected region of lumbar sympathetic nerves in the anterolateral prevertebral space and to confirm at least three vertebral body lengths of distribution. In two patients with bilateral disease, this procedure was repeated on the contralateral side. In one patient, limited craniocaudal distribution of the injected agent required placement of a second needle at level L4 and additional injection of 10 mL of anesthetic agent.
The surface coil was replaced over the pelvis at 20 minutes after therapeutic injection, and additional velocity-encoded images were obtained of the common femoral vessels. The coil was then repositioned over the knees, and images were obtained of the popliteal vessels. Changes in skin surface temperature as indicated by the adhesive liquid crystal thermometers were recorded (by the attendant nurse) to the nearest 0.5°C. Patients were asked to rate their limb pain on a scale of 1 to 10 to evaluate anesthetic response. Skin coloration was periodically inspected (D.Y.S., S.C.M.). The entire procedure required approximately 2 hours, including 30–45 minutes of preprocedural imaging, 30–45 minutes of needle placement and agent injection, and 30–45 minutes of postinjection imaging and observation.
In two patients in whom symptoms were temporarily alleviated but recurred within 10 days, repeat treatment with bupivacaine hydrochloride was performed 11 days later (patient 4), and a neurolytic sympathectomy was performed with 8 mL of 10% phenol in aqueous solution 19 days later (patient 7). Patient 6, who had temporary relief from a previous fluoroscopy-guided bupivacaine hydrochloride treatment, also underwent a neurolytic sympathectomy with phenol solution as part of this study. Chemical sympathectomy was performed in patients who wished to avoid surgical sympathectomy but required longer periods of efficacy.
In patient 2, with CRPS of bilateral lower extremities, previous fluoroscopy-guided sympathetic nerve blockade provided a period of analgesia and partial recovery, and a longer period of anesthetic administration was desired. In this patient, bilateral 20-gauge indwelling catheters designed for epidural infusions (Braun, Bethlehem, Pa) were inserted through 18-gauge introducing needles (Cook), tunneled subcutaneously, and fitted with hubs after the introducing needle was removed. Initial 3-mL test dose and 15-mL therapeutic dose injections were administered via the catheters, and the distribution was imaged as described previously. Continuous infusion of 0.125% bupivacaine hydrochloride at a rate of 5 mL/h into each catheter was then performed over 6 days with intensive physical therapy, after which the catheters were removed.
In patient 3, the left shoulder was injured in a football game, which led to CRPS of the entire extremity. Previous fluoroscopy-guided stellate ganglion block provided brief relief, and an implanted catheter was also requested. Flow imaging, needle guidance, and catheter placement techniques were adapted for application to the stellate ganglion, and instead of femoral and popliteal vessels, common carotid, internal jugular, and subclavian vessels were imaged in transverse and sagittal planes. Anesthetic and motor and sensory radicular effects were evaluated by asking the patient to rate his pain on a scale of 10, by subjectively rating the patient’s grip strength, and by performing cutaneous pin pricks. An indwelling catheter was inserted and tunneled subcutaneously, and 0.25% bupivacaine hydrochloride was continuously administered at a rate of 5 mL/h for 2 days.
Patient characteristics and treatments are summarized in Table 1: In seven patients, 11 limbs were treated during nine procedure sessions. The first two patients underwent imaging in both prone and supine positions to determine whether the prone position compressed the femoral vessels and restricted blood flow. No noticeable difference was seen between prone and supine positions, and subsequently, all patients underwent imaging in only the prone position to minimize repositioning of the patient and coil.
Quantitation of flow was performed (D.Y.S.) with the program and technique described by Pelc et al (11). Volumetric flow was calculated by integration of velocities over each of 16 partitions of the cardiac cycle, gated by fingertip plethysmography. Flow in the arteries and veins was independently calculated, and the total volume of blood flow through a region was calculated as the average of the mean arterial and venous flows. In some patients, popliteal veins were duplicated or substantial flow was detected in greater saphenous veins, and the total venous flow was calculated as the sum of the flows in the individual vessels. Flow in each of the cardiac cycle partitions was plotted to obtain pulse-volume curves. Prior validation studies in phantoms and in human subjects indicated method variability and error to be within 10% (12,13). Peak systolic cross-sectional diameters of the arteries and veins were also measured on the MR images.
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Results
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Procedures were successfully completed in all nine attempts and 11 limbs. The optimal pulse sequence for visualizing the target, needle, and injected agent differed for each patient. Specifically, documentation of the distribution of injected agent was best seen on T1-weighted fast spin-echo images in some patients (in six patient visits in four patients to treat seven limbs), on gradient-echo images in some (in one patient visit in one patient to treat two limbs), and on fast imaging with steady-state precession images in others (two patient visits in two patients to treat two limbs). For patients who underwent lumbar sympathetic blockade, needle tips were positioned so that test injections of anesthetic agent were seen to course in the paravertebral space anteromedial to the psoas muscle. In all but one patient, the 15 mL of injected therapeutic agent channeled in a craniocaudal direction to span three vertebral bodies, usually from L1 to L4 (Fig 1). One patient showed only about two vertebral body lengths of distribution and required an additional 10-mL injection at L4.
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Figure 1a. T1-weighted fast spin-echo MR images (500/19 [effective]) in a prone patient with multiple sclerosis complicated by CRPS and erythromelalgia. (a) Oblique sagittal and (b) oblique transverse images depict placement of a 20-gauge needle (arrows) to the expected region of the lumbar sympathetic plexus, anterolateral to L2. (c) Sagittal and (d) oblique transverse images delineate the distribution (arrows) of injected anesthetic agent (15 mL of 0.25% bupivacaine hydrochloride doped with 1:100 gadolinium-based contrast agent).
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Figure 1b. T1-weighted fast spin-echo MR images (500/19 [effective]) in a prone patient with multiple sclerosis complicated by CRPS and erythromelalgia. (a) Oblique sagittal and (b) oblique transverse images depict placement of a 20-gauge needle (arrows) to the expected region of the lumbar sympathetic plexus, anterolateral to L2. (c) Sagittal and (d) oblique transverse images delineate the distribution (arrows) of injected anesthetic agent (15 mL of 0.25% bupivacaine hydrochloride doped with 1:100 gadolinium-based contrast agent).
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Figure 1c. T1-weighted fast spin-echo MR images (500/19 [effective]) in a prone patient with multiple sclerosis complicated by CRPS and erythromelalgia. (a) Oblique sagittal and (b) oblique transverse images depict placement of a 20-gauge needle (arrows) to the expected region of the lumbar sympathetic plexus, anterolateral to L2. (c) Sagittal and (d) oblique transverse images delineate the distribution (arrows) of injected anesthetic agent (15 mL of 0.25% bupivacaine hydrochloride doped with 1:100 gadolinium-based contrast agent).
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Figure 1d. T1-weighted fast spin-echo MR images (500/19 [effective]) in a prone patient with multiple sclerosis complicated by CRPS and erythromelalgia. (a) Oblique sagittal and (b) oblique transverse images depict placement of a 20-gauge needle (arrows) to the expected region of the lumbar sympathetic plexus, anterolateral to L2. (c) Sagittal and (d) oblique transverse images delineate the distribution (arrows) of injected anesthetic agent (15 mL of 0.25% bupivacaine hydrochloride doped with 1:100 gadolinium-based contrast agent).
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In patient 3, in whom stellate ganglion block was attempted, the initial test injection after needle placement confirmed the desired position. However, when the closed-tip catheter was threaded through the needle, it inadvertently dissected into the epidural space at C7. Injection of bupivacaine hydrochloride solution doped with 1:100 gadolinium-based contrast agent enhanced only the epidural space and not the region of the stellate ganglion. The patient exhibited hypoesthesia of bilateral upper extremities and mild motor weakness, with a greater effect in the contralateral arm and chest. No respiratory depression or other complications were noted. Because the degree of anesthesia correlates with the efficacy of treatment of CRPS (14) and because this epidural injection was producing effective hypoesthesia, we proceeded with epidural infusion despite lack of evidence of sympatholysis. Infusion was continued for 48 hours without difficulty, after which the catheter was removed. No evidence of inadvertent somatic nerve damage was detected in the patients undergoing lumbar sympathetic blockade.
The maximum temperature readings of the affected limbs increased from less than 34°C (below the lower limit of the thermometer scale) to a mean of 36.5°C (range, 35.5°C–38.0°C). (Temperatures indicated by the liquid crystal thermometers are corrected for core temperature and are approximately 1.5°C higher than the actual skin temperature. Thus, a reading of 38°C indicates a true skin temperature of 36.5°C. Visual inspection of the limbs revealed resolution of livedo and cyanosis and a geographic but progressively confluent rubor in the patients with CRPS and erythromelalgia. Increased rubor was also noted in the patients with fixed lesions, but the findings were more subtle. All seven patients after all nine procedures reported subjective analgesia, increased warmth, and pulsatility of all 11 affected limbs. However, subjective analgesia proved impossible to quantify, mostly due to the narcotic and amnestic effects of the intravenous sedation. In the younger patients without fixed lesions (patients 1–4), both arteries and veins increased in luminal diameter (Fig 2). Common femoral arteries (common carotid artery in patient 3) in these patients increased in diameter by a mean of 23% (range, 11%–30%) and common femoral veins (internal jugular vein in patient 3) by a mean of 57% (range, 20%–100%).
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Figure 2a. Baseline peak systolic transverse velocity-encoded cine MR images (20/9.1; velocity encoding, 150 cm/sec) in the (a) common femoral region and (b) popliteal region in a supine patient with multiple sclerosis complicated by CRPS and erythromelalgia. Arteries (white arrows) and veins (black arrows) demonstrate opposite directions of flow. (c, d) MR images obtained after bilateral blockade at the same levels show dilatation of the arteries (white arrows) and veins (black arrows), higher signal intensity within the lumina, and the appearance of flow in the greater saphenous veins (arrowheads in d).
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Figure 2b. Baseline peak systolic transverse velocity-encoded cine MR images (20/9.1; velocity encoding, 150 cm/sec) in the (a) common femoral region and (b) popliteal region in a supine patient with multiple sclerosis complicated by CRPS and erythromelalgia. Arteries (white arrows) and veins (black arrows) demonstrate opposite directions of flow. (c, d) MR images obtained after bilateral blockade at the same levels show dilatation of the arteries (white arrows) and veins (black arrows), higher signal intensity within the lumina, and the appearance of flow in the greater saphenous veins (arrowheads in d).
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Figure 2c. Baseline peak systolic transverse velocity-encoded cine MR images (20/9.1; velocity encoding, 150 cm/sec) in the (a) common femoral region and (b) popliteal region in a supine patient with multiple sclerosis complicated by CRPS and erythromelalgia. Arteries (white arrows) and veins (black arrows) demonstrate opposite directions of flow. (c, d) MR images obtained after bilateral blockade at the same levels show dilatation of the arteries (white arrows) and veins (black arrows), higher signal intensity within the lumina, and the appearance of flow in the greater saphenous veins (arrowheads in d).
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Figure 2d. Baseline peak systolic transverse velocity-encoded cine MR images (20/9.1; velocity encoding, 150 cm/sec) in the (a) common femoral region and (b) popliteal region in a supine patient with multiple sclerosis complicated by CRPS and erythromelalgia. Arteries (white arrows) and veins (black arrows) demonstrate opposite directions of flow. (c, d) MR images obtained after bilateral blockade at the same levels show dilatation of the arteries (white arrows) and veins (black arrows), higher signal intensity within the lumina, and the appearance of flow in the greater saphenous veins (arrowheads in d).
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Quantitative analysis of velocity-encoded cine images demonstrated increased blood flow to the affected extremities after sympathetic nerve blockade in all patients (Table 2). Increases in volume of flow in the femoral region ranged from 17% to 485% (mean, 180%) and in the popliteal region ranged from 15% to 975% (mean, 235%). The patients with fixed lesions that involved irreversible vascular occlusions (atherosclerosis, scleroderma) responded less dramatically than those suspected of having autonomic dysfunction (15%–52% increase vs 92%–975% increase) (Fig 3). Interestingly, patient 5, who had thromboangiitis obliterans and abused a variety of drugs, including tobacco, exhibited a marked increase in blood flow of 485% after nerve blockade. This is despite having fixed arterial occlusions documented at angiography, which suggests that his limb ischemia included a substantial component of autonomic dysfunction. Also of interest in the seven procedures that were unilateral, six patients demonstrated some decrease in measured blood flow in the contralateral limb.
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Figure 3. Bar graph depicts patient responses by limb characteristics. Minor negative changes occurred in untreated limbs (1, femoral region; 2, popliteal region). Small positive changes occurred in treated limbs with disease that involved fixed arterial obstructions (3, femoral region; 4, popliteal region). Large changes occurred in treated limbs without fixed arterial obstructions (5, femoral region; 6, popliteal region). The single large responder in group 3 was the patient with Burgher disease (see Results and Discussion).
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The velocity-encoded cine images were pulse gated and partitioned into 16 images per cardiac cycle, and pulse volume tracings were generated for each vessel. In addition to increasing the peak systolic flow, sympathetic blockade had a profound effect on increasing diastolic flow (Fig 4). Waveforms before blockade were of the typical high-resistance muscular pattern, triphasic in the younger patients and mono- or biphasic in those with fixed lesions. At the end of systole, flow was frequently reversed in direction. After blockade, systolic and diastolic arterial flow and venous flow were all increased. Arterial flow was antegrade throughout the cardiac cycle with blunting of the pulsatility, which indicated decreased peripheral vascular resistance.
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Discussion
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Disruption of the sympathetic nervous system has proved useful in a number of vascular diseases where heightened autonomic tone may cause or exacerbate ischemia (1,15). Numerous methods of disruption of the sympathetic nervous system are feasible, including surgical sympathectomy, percutaneous chemical neurolysis, radio-frequency ablation, and percutaneous anesthetic blockade (1,15–17). Each of these methods has different expected durations of efficacy, risks, and technical difficulties. The pursuit of minimum invasiveness has been accelerated by the increased use of imaging-guided percutaneous techniques, which in turn have been facilitated by improved imaging technology. Although many procedures can still be performed safely with use of only anatomic landmarks or of only fluoroscopy, the advantages of cross-sectional imaging guidance are becoming better defined (6,18). This is particularly true in patients with anomalous or distorted anatomy due to surgery, tumor, or scarring (8,18).
Encouraging initial results with MR imaging for imaging guidance of regional nerve blockade were reported (8). For these patients, efficacy was evaluated with the conventional methods of interviewing patients about subjective pain relief, observing skin color, and palpating skin temperature. Although undeniable objective findings could be documented, these pilot studies were performed without controls, and in both that study and the present study, subjective questionnaires were unreliable after patients received intravenous sedatives. In another recently published report, MR imaging-guided celiac plexus blocks were performed and evaluated by means of subjective pain questionnaires (19). The feasibility of an independent, objective, and quantitative measurement of efficacy is thus especially attractive.
All of our patients experienced pain syndromes related to ischemia; thus, measurement of blood flow to the affected limb was considered an objective measurement of treatment efficacy that tended less toward the inaccuracies of subjective pain questionnaires and problematic concerns about the ethics of including a placebo control group (20–24). Blood flow can be measured with Doppler US, laser Doppler perfusion imaging, plethysmography, thermography, or scintigraphy (20,22,24–26), but the instruments required for these techniques are not compatible with MR imaging. Cine MR imaging techniques have been used to quantify blood flow in peripheral arteries in athletes and patients with atherosclerosis (9,27,28). With the same MR imaging hardware used for MR imaging guidance of the blockade procedure and with minimal patient manipulation, we were able to quantify the blood flow in affected limbs before and after sympathetic nerve blockade. Another group reported a different method of using MR imaging to quantify flow after stellate ganglion blockade with use of a contrast material bolus-tracking technique (21). This method required use of intravenous contrast material and yielded only arterial velocities and not volumetric flow.
The patients who demonstrated the greatest increases in measured blood flow were also the ones who exhibited the greatest increases in skin temperature and rubor. Evidently, these patients with CRPS or multiple sclerosis with erythromelalgia had autonomic dysfunction as a major component of their neurovascular pain syndromes. The magnitude of flow increases is comparable with the changes seen after physical exercise, as measured with MR imaging (28), and is comparable with the changes seen after sympathetic nerve block as measured with laser Doppler (22,26). As would be expected, the patients with fixed occlusive disease demonstrated more modest increases in blood flow. In these patients, the cause of ischemia involved permanent destruction of blood vessels (atherosclerosis, scleroderma), which would not be reversible with any manipulation of the autonomic nervous system. However, these modest increases may be clinically important; in our patients, they allowed chronic nonhealing ulcers to heal.
The substantial increase in measured blood flow in the patient with thromboangiitis obliterans exceeded expectations. Thromboangiitis obliterans involves arterial occlusions with development of "corkscrew" collateral vessels, and we expected this patient to respond similarly to the other patients with fixed occlusive diseases. However, the fivefold increase in common femoral flow appeared to reveal a large component of autonomic dysfunction and supports further investigation of sympathetic nerve blockade for the treatment of this debilitating vasculopathy (29).
Of the seven patients who underwent unilateral procedures, six appeared to demonstrate a decrease in measured blood flow in at least one vessel on the contralateral side. The sympathetic plexus may include crossover circuits, and unilateral manipulation may have bilateral effects (30). In these six patients, however, the observed contralateral decrease in blood flow raises the issue of a steal phenomenon or a reflex compensatory vasoconstriction. For patients with bilateral symptoms, unilateral treatment may require special caution to avoid exacerbation of contralateral symptoms, but this will require further investigation.
Other methods of sympathetic nerve blockade or neurolysis, including surgical sympathectomy (31), cryogenic ablation (17), and radio-frequency ablation (16), are also available. Surgical sympathectomy is considered by some to be the best technique because the other methods appear to have higher failure rates. Injected agents can be imaged by mixing them with radiopaque contrast material and using fluoroscopic or CT guidance (18) or by adding a radionuclide and imaging with scintigraphy (32). One other MR imaging study to track the distribution of injected agents after stellate ganglion blockade showed that the actual distribution differed from the expected, which suggests that the theoretic mechanism of action may be incorrect or that refinements of technique may be beneficial (33). Cryogenic and radio-frequency ablations are considerably more difficult to monitor, which could account in part for the lower efficacy rates. The efficacy of these techniques could be reevaluated now that there is the capability to monitor tissue destruction and resultant changes in blood flow with MR imaging.
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FOOTNOTES
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Abbreviation: CRPS = complex regional pain syndrome
Author contributions: Guarantor of integrity of entire study, D.Y.S.; study concepts and design, S.C.M., D.Y.S.; literature research, D.Y.S.; clinical studies, D.Y.S., S.C.M.; data acquisition, D.Y.S., S.C.M.; data analysis/interpretation, D.Y.S.; manuscript preparation and definition of intellectual content, D.Y.S.; manuscript editing and revision/review, D.Y.S., S.C.M.; manuscript final version approval, D.Y.S.
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M. R. Schmid, R. O. Kissling, A. Curt, G. Jaschko, and J. Hodler
Sympathetic Skin Response: Monitoring of CT-guided Lumbar Sympathetic Blocks
Radiology,
November 1, 2006;
241(2):
595 - 602.
[Abstract]
[Full Text]
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ABSTRACT
INTRODUCTION
) and after (
) sympathetic blockade of the (a) left femoral artery, (b) left femoral vein, (c) left popliteal artery, and (d) left popliteal vein. Flow in the saphenous vein was undetectable before nerve blockade. 
in d = after treatment in the saphenous vein.
