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Paranephric Water Instillation: A Technique to Prevent Bowel Injury During Percutaneous Renal Radiofrequency Ablation

¹ Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
² Department of Urology, Mayo Clinic, Rochester, MN 55905.

Received March 11, 2003; accepted after revision May 1, 2003.

 
Address correspondence to M. A. Farrell.

Introduction

Top Introduction Case 1 Case 2 Discussion References

 
Radiofrequency ablation is a promising new minimally invasive treatment option for solid renal tumors in a select group of patients with a low incidence of side effects [1, 2]. The close relationship of tumors to critical structures may make the lesion unsuitable for percutaneous ablation. When the bowel lies adjacent to the tumor, it increases the risk of thermal bowel injury and perforation [3]. Although repositioning the patient may cause displacement of the bowel, it is not always successful, necessitating either a surgical partial nephrectomy or a radiofrequency ablation performed as an open or laproscopic procedure. Most patients referred for renal radiofrequency ablation are not good surgical candidates, and avoidance of a surgical procedure would be optimal.

We describe a technique we have successfully used to safely treat two renal tumors in close proximity to the bowel by displacing the bowel away from the tumor with imaging-guided percutaneously instilled sterile water. We refer to this technique as hydrodis-placement of the bowel.

Case 1

Top Introduction Case 1 Case 2 Discussion References

 
A 45-year-old woman with von Hippel-Lindau disease was referred for the treatment of two solid enhancing left renal masses noted on CT. She had a history of bilateral partial nephrectomies for multiple renal cell carcinomas. One of the lesions measured 1.5 cm in diameter and was in the anterior mid kidney adjacent to the descending colon. Sterile water (135 mL) was instilled into the tissues between the anterior aspect of the kidney and the adjacent descending colon using a 21-gauge spinal needle under sonographic guidance. This resulted in the bowel being displaced approximately 2.5 cm from the anterior aspect of the renal tumor. The tumor was then treated for 12 min with a 2-cm single-tip active electrode using the Radionics system (Burlington, MA). Contrast-enhanced CT performed 4 hr after the procedure showed complete ablation of the tumor and no evidence of bowel injury. Repeated CT 2 months after ablation showed no evidence of residual or recurrent tumor, and the adjacent bowel had a normal appearance.

Case 2

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The second patient was a 49-year-old woman with von Hippel-Lindau disease referred for percutaneous radiofrequency ablation of two solid enhancing renal tumors seen on CT, one in each kidney. She had a history of multiple right partial nephrectomies for renal cell carcinomas. A 1.3-cm mass in the left kidney arose exophytically from the anterior lower pole adjacent to the jejunum and colon (Fig. 1A). Placement of the patient in an oblique or lateral position did not effectively displace the adjacent small bowel and colon. Using a 20-gauge spinal needle, we instilled sterile water (150 mL) with real-time sonographic guidance into the space anterior to the tumor for approximately 2 min. Repeated CT after the instillation of water showed the bowel to be displaced 2.1 cm from the tumor, an adequate margin for radiofrequency ablation to proceed (Fig. 1B). The tumor was then treated for 9 min with a 2-cm single-tip active electrode using the Radionics system. Fluoroscopic CT images were obtained intermittently during the ablation to ensure that an adequate safety margin persisted during the procedure. Contrast-enhanced CT performed immediately after the procedure showed complete ablation of the tumor and no evidence of bowel injury (Fig. 1C). The patient remained asymptomatic for the observation period of 6 weeks after the radio-frequency ablation treatment.

View larger version (162K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —49-year-old woman with von Hippel-Lindau disease and prior right partial nephrectomies for renal cell carcinoma. Axial, contrast-enhanced CT image shows small enhancing exophytic tumor (straight arrow) arising from lower pole of left kidney, adjacent to small bowel (open arrow) and colon (curved arrow).

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —49-year-old woman with von Hippel-Lindau disease and prior right partial nephrectomies for renal cell carcinoma. Unenhanced axial CT image obtained after sonographically guided instillation of water (large curved arrow) at time of radiofrequency ablation shows small bowel (open arrow) and colon (small curved arrow) to have been lifted off tumor (long straight arrow). Tiny locules of air were injected with water (black arrow).

View larger version (153K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —49-year-old woman with von Hippel-Lindau disease and prior right partial nephrectomies for renal cell carcinoma. Contrast-enhanced CT image obtained immediately after radiofrequency ablation shows normal appearance of small bowel (open arrow) and colon (small curved arrow) and lack of enhancement in ablated tumor (black arrow). Some water has diverted laterally (large curved arrow).

Discussion

Top Introduction Case 1 Case 2 Discussion References

 
Radiofrequency ablation of renal tumors has recently been described as a nephron-sparing, minimally invasive option for the treatment of renal tumors and is typically reserved for patients who are not surgical candidates [1, 2]. It can be performed percutaneously using imaging guidance or surgically using either an open or laproscopic approach. In our practice, the percutaneous approach is contraindicated for treatment of lesions that are within 1 cm of the bowel because visceral injury has been reported in radiofrequency ablation of a pig liver model when the edge of the thermal lesion was less than 1 cm from the liver surface [3]. Colonic and jejunal thermal injury resulting in perforation has been previously reported during human liver radiofrequency ablation [4]. Therefore, tumors adjacent to the bowel that are referred for percutaneous ablation are typically deferred for either a partial nephrectomy or radiofrequency ablation using a laparoscopic or open approach. In our institution, approximately 50% of patients referred for radiofrequency ablation have a medical comorbidity (excluding prior partial or total nephrectomy) that precludes surgery [1]. Therefore, a technique that allows safe percutaneous ablation of renal lesions adjacent to bowel that traditionally would have required an open or laproscopic ablation approach appears desirable for these patients.

Ohmoto and Yamamoto [5] created artificial ascites with 40–50 mL of 0.5% lidocaine to treat a superficial hepatocellular carcinoma and prevent thermal injury to the abdominal wall while performing percutaneous microwave coagulation. They also described using 300–400 mL of saline to create artificial ascites to improve tumor conspicuity by separating the lung and liver in a different patient with a hepatocellular carcinoma in the dome of the liver that was then treated with percutaneous microwave [6]. To our knowledge, a technique has not been described regarding bowel displacement when using percutaneous radiofrequency ablation for renal masses.

The parameter governing tissue destruction during radiofrequency ablation is temperature, and the volume of ablation is governed by the temperature distribution within the lesion. However, a bowel that is contiguous with the renal tumor is also at risk for thermal injury and perforation. The amount of heat that is conducted from the edge of the ablation volume to the adjacent bowel is inversely proportional to the distance between them. Therefore, increasing this interval distance with water, which has a low thermal conductivity, reduces the thermal conduction between the tumor and the bowel and protects the bowel from thermal injury.

In addition, water has another advantage over saline. For a given total radiofrequency current, the power deposition at each point in space is strongly dependent on the local conductivity. Injection of saline into the targeted tissue during ablation leads to an increase in the ablated tissue volume by increasing the electric conductivity because of the strongly ionic nature of saline [7]. Although this technique does not involve the injection of fluid directly into the targeted tissue, water is preferred over saline to reduce the risk of an unpredictable zone of thermal ablation. No obvious heat sink effect occurred from locating the water adjacent to the tumor. Prolonged ablation times were not required; both tumors required 12 and 9 min of ablation time. The water is at room temperature and stagnant and therefore unlikely to lead to significant heat loss.

Sonography is the guiding modality of choice in our practice for the ablation of renal masses. However, we advocate using CT guidance as a monitoring method when hydrodis-placement is being used. Bowel can be difficult to visualize on sonography, whereas CT accurately shows the bowel and its displacement with water from the overlying tumor. Also, to ensure that the instilled water provides adequate displacement of bowel from the entirety of the ablation area, we recommend intermittent fluoroscopic CT. Water may divert away from the intended site and cause the bowel to remain adjacent to the tumor surface. During the ablation treatment, gas is produced. When using sonography, this procedure causes a shadowing artifact because of its high acoustic impedence, which obscures the area and makes assessment of adequate bowel displacement difficult.

In summary, we have found hydrodis-placement to be a useful technique for safely treating renal tumors that are in close proximity to the bowel.

References

Top Introduction Case 1 Case 2 Discussion References

 

1. Farrell MA, Charboneau WJ, DiMarco DS, el al. Imaging-guided radiofrequency ablation of solid renal tumors. AJR2003; 180:1509 –1513[Abstract/Free Full Text]
2. Gervais DA, McGovern FJ, Arellano RS, et al. Renal cell carcinoma: clinical experience and technical success with radiofrequency ablation of 42 tumors. Radiology2003; 226:417 –424[Abstract/Free Full Text]
3. Hansen PD, Rogers S, Corless CL, et al. Radiofrequency ablation lesions in a pig liver model. J Surg Res1999; 87:114 –121[Medline]
4. Livraghi T, Solbiati L, Meloni MF, et al. Treatment of focal liver tumors with percutaneous radiofrequency ablation: complications encountered in a multicenter study. Radiology2003; 226:441 –451[Abstract/Free Full Text]
5. Ohmoto K, Yamamoto S. Percutaneous microwave coagulation therapy using artifical ascites. AJR2001; 176:817 –818[Free Full Text]
6. Ohmoto K, Tsuzuki M, Yamamoto S. Percutaneous microwave coagulation therapy with intraperitoneal saline infusion for hepatocellular carcinoma in the hepatic dome. AJR1999; 172:65 –66[Free Full Text]
7. Goldberg SN, Ahmed M, Gazelle GS, et al. Radiofrequency thermal ablation with NaCl solution injection: effect of electrical conductivity on tissue heating and coagulation—phantom and porcine liver study. Radiology2001; 219:157 –165[Abstract/Free Full Text]

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