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Technical Innovation |
1 Both authors: The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins Hospital, Jefferson Bldg., Rm. 173, 600 N Wolfe St., Baltimore, MD 21287.
Received September 12, 2003;
accepted after revision November 25, 2003.
Address correspondence to S. B. Solomon.
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We report three techniques used to prevent collateral damage to nearby normal structures. A small amount of air was used in the first case to displace a loop of intestine before thermal ablation of an adjacent exophytic renal mass. The second case involved torquing the radiofrequency probe within the kidney to move the kidney away from a loop of bowel. The third case involved applying an ice pack to the skin overlying a superficial paraspinal mass to prevent a skin burn.
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In our first case, an 80-year-old woman who had previously undergone a right nephrectomy for transitional cell carcinoma was incidentally found to have a 3-cm homogeneously enhancing exophytic mass and a 2.5-cm intraparenchymal heterogeneous mass, both at the lower pole of the left kidney. Subsequent CT-guided percutaneous biopsies of the lesions were positive for renal cell carcinoma. The interventional radiology department was consulted in an effort to spare the mid and upper poles of the solitary left kidney by performing percutaneous thermal ablation under local anesthesia.
Under CT fluoroscopy guidance (Somatom Plus 4, Siemens) with the patient in an obliquely supine position, a radiofrequency probe (Starburst XL, Rita Medical Systems) was percutaneously inserted into the left lower pole exophytic renal mass. After complete ablation, the intraparenchymal lower pole mass was targeted. Unenhanced CT scans of the region revealed a loop of small intestine that had moved during the interval to within 8 mm of the left lower pole renal mass. A second percutaneous entry site was then created in the left flank; and under CT fluoroscopy guidance, a 22-gauge Chiba needle (Cook) was introduced between the targeted lesion and the small intestine (Fig. 1A). Three milliliters of air was injected through the Chiba needle, successfully displacing the loop of small intestine away from the adjacent renal mass (Fig. 1B). Thermal ablation was performed for approximately 18 min according to the manufacturer's protocol. CT fluoroscopy was intermittently used during ablation to ensure that no thermal damage was occurring to the adjacent small bowel. No complications occurred, and the patient had no related sequelae.
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In our second case, a 60-year-old woman who previously underwent a left nephrectomy for renal cell carcinoma was referred to the interventional radiology department for radiofrequency ablation of a metastatic lesion in the right kidney. The patient successfully underwent radiofrequency ablation of this 3-cm lesion as an outpatient. Follow-up contrast-enhanced CT of the abdomen performed 6 weeks later showed a focal area of nodular enhancement adjacent to the previously treated right renal mass. Although biopsy did not show residual cancer, the patient returned to the interventional radiology department for repeated radiofrequency ablation of the questionable area.
The patient was placed in the prone position, and under CT fluoroscopy guidance, a 2-cm radiofrequency probe (Boston Scientific) was placed in the lesion. CT performed just before ablation showed a loop of bowel that was not present during the first ablation immediately lateral to the lesion (Fig. 2A). In an effort to minimize thermal injury to the adjacent bowel, the handle of the radiofrequency probe was maneuvered inferiorly under CT fluoroscopy guidance, displacing the kidney and the tip of the probe superiorly by approximately 1 cm (Fig. 2B). This maneuver successfully displaced the kidney enough to prevent thermal injury to the adjacent loop of bowel during subsequent ablation. CT fluoroscopy was intermittently used during the ablation to ensure the integrity of the adjacent intestine.
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Our third case involved a 60-year-old man who presented to his primary care physician with a 1-year history of back pain. Thoracic and lumbar spine MRI revealed a 5-cm right paraspinal mass at the level of T-12 with chest wall extension and erosion into the adjacent vertebral body and right 12th rib. Biopsy of the mass revealed poorly differentiated carcinoma from an unknown primary tumor.
After one round of palliative chemotherapy, the patient's back pain worsened. After discussion with his oncologist, the patient elected an attempt at pain control via a CT-guided percutaneous radiofrequency ablation of the paraspinal mass under general anesthesia. Under CT fluoroscopy guidance, a radiofrequency probe (Starburst XL) was percutaneously placed in the center of the lesion. Because of the superficial location of the lesion, a temperature probe (Rita Medical Systems) was placed on the skin overlying the targeted lesion, and readings were displayed on the radiofrequency generator unit. The baseline skin temperature was 35°C. After the position of the radiofrequency probe within the targeted lesion was again confirmed, the radiofrequency generator was switched on. The skin overlying the targeted mass was directly observed throughout the procedure for signs of tissue damage (erythema, blistering, swelling). After 8 min, the skin temperature reached a maximum of 38°C with no visible signs of tissue damage. The radiofrequency generator was immediately turned off, the radiofrequency probe was kept in place, and an ice pack (Kwik-Kold, Allegiance Healthcare) was placed on the overlying skin (Fig. 3). After 3 min, the skin cooled to a temperature of 32°C, with no change in appearance. The ablation was continued and completed after another 15 min, for a total ablation time of 23 min. After the resumption of radiofrequency ablation, the maximum skin temperature recorded was 36°C. No complications occurred, and the patient had no related sequelae.
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A number of maneuvers have recently been described that may be used to limit injury to adjacent bowel. Ogan et al. [6] reported placing the patient in a modified (30°) prone position to displace an adjacent loop of small intestine. Rendon et al. [7] reported hydrodissection (saline) and gas dissection (CO2) techniques during porcine renal radiofrequency ablation to protect adjacent structures. Recent animal experiments in our laboratory suggest that using air or a contrast-filled balloon placed between targeted and nontargeted structures limits the spread of thermal energy (Solomon SB, unpublished data).
In our first patient, 3 mL of air was introduced between the targeted exophytic renal lesion and the adjacent small bowel before successful radiofrequency ablation. An alternative to air would be CO2, which has the advantage of rapid dissolution if inadvertently injected IV.
In the second case, we successfully maneuvered the radiofrequency probe, thereby percutaneously moving the kidney away from an adjacent loop of small bowel. Retraction, a common surgical technique for moving organs, was applied in this case to separate the ablation target from the bowel. Radiofrequency ablation of the target area was successfully completed, again without thermal injury to the small bowel.
Most reported skin burns involve improper sizing or placement of the grounding pad, which serves as a dispersive electrode in a radiofrequency circuit [1]. Undersized grounding pads do not properly disperse the radiofrequency energy (heat) over a wide enough area, thereby causing a skin burn. Likewise, skin burns may be caused by incomplete contact between the grounding pad and the underlying skin. Skin burns have also been reported at the probe insertion site. Yamagami et al. [5] reported a patient in whom damage to the insulating coating surrounding the ablation probe caused a focal skin burn. Bilchik et al. [8] described a patient who sustained a third-degree skin and abdominal wall burn during the tract ablation portion of percutaneous ablation. In the third patient whom we described, we successfully prevented a skin burn during percutaneous radiofrequency ablation of a superficial soft-tissue mass using a combination of real-time skin temperature monitoring and direct skin cooling.
Percutaneous CT-guided radiofrequency ablation of solid tumors is a promising technique. As the number of procedures performed increases, so too will the number and the variety of reported complications associated with the technique. In this article, we describe three maneuvers to prevent thermal damage to surrounding structures. Although larger series of patients are needed to further evaluate these techniques, we believe that these maneuvers could prove useful in preventing unnecessary complications.
Acknowledgments
We thank William Lao and Mindao Chen for their assistance with the in vitro
work mentioned in this manuscript.
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