Patrick E. Sewell

PERCUTANEOUS RENAL TUMOR CRYOABLATION WITH MAGNETIC RESONANCE IMAGING GUIDANCE

PURPOSE Cryoablation of small renal tumors has been performed mainly via the laparoscopic or open approach. This study was done to assess the feasibility and safety of performing percutaneous renal tumor cryoablation using interventional magnetic resonance imaging (MRI) for monitoring. MATERIALS AND METHODS Patients with radiography documented small renal tumors 4 cm or less in diameter were offered percutaneous renal tumor cryoablation performed in an interventional MRI unit. Patients received general anesthesia or intravenous sedation and were placed into the interventional MRI unit. Under MRI guidance a 2 or 3 mm cryoprobe was advanced into the renal mass and the mass was subjected to 3 freeze-thaw cycles at -80 to 70C. Patients were hospitalized overnight for observation. Followup imaging with MRI or computerized tomography and physical examinations were done at 1 week, and 1, 3, 6 and 12 months. RESULTS Ten men and 10 women 49 to 76 years old (mean age 58) with a total of 22 tumors have been treated, including 1 with bilateral lesions and another with 2 tumors in 1 kidney. Mean tumor diameter was 3 cm. (range 1.8 to 7.0). Two patients with a mass exceeding study entry criteria (5 and 7 cm, respectively) who were not open surgery candidates were treated on a compassionate basis. Average treatment time was 97 minutes (range 56 to 172). To date 1 patient has had evidence of persistent tumor on followup imaging and required re-treatment. The only complication was a superficial wound abscess. Mean followup was 9.1 months (range 3 to 14) with no radiographic evidence of disease recurrence or new tumor development. CONCLUSIONS In this small series of patients percutaneous renal tumor cryoablation was technically feasible with minimal morbidity. At limited followup there appears to be no radiological evidence of new tumor development. Percutaneous cryoablation may prove to be an additional treatment option for small renal tumors.

Interventional magnetic resonance image-guided percutaneous cryoablation of renal tumors.

We describe the first two cases of percutaneous cryoablation under magnetic resonance imaging guidance. To date, this minimally invasive procedure has been used for the treatment of renal cell tumors in patients who cannot tolerate or refuse surgical nephrectomy. The two patients described showed no evidence of recurrence or complications 35 and 36 months after the procedure.

PERCUTANEOUS CRYOABLATION OF PORCINE KIDNEYS WITH MAGNETIC RESONANCE IMAGING MONITORING

PURPOSE We determined the feasibility of a percutaneous approach using magnetic resonance imaging (MRI) for creating cryoablation lesions in the porcine kidney. METHODS AND METHODS Three domestic swine underwent renal cryoablation under MRI guidance with a total of 6 cryoablation lesions created in 5 kidneys. A 3 mm. cryoprobe was placed under MRI guidance using an interventional MRI unit. With a pressurized argon gas cooling unit the cryoablation lesion was created and monitored by MRI. Gross and histological examination of the kidneys was performed 1 week after the procedure. RESULTS All animals survived the procedure without difficulty. A total of 6 cryoablation lesions were produced in 5 kidneys. The lesions were 1.9 x 1.3 to 3.9 x 1.9 cm. on MRI. Histological examination 1 week after treatment showed that the lesions were 1.7 x 1.0 to 3.2 x 1.2 cm. There was an area of coagulation necrosis surrounded by a transition zone of inflammatory reaction a mean of 0.5 cm. in diameter with each lesion. CONCLUSIONS Percutaneous renal cryoablation using MRI imaging proved to be a successful technique for guiding probe placement and monitoring ice ball formation. Because MRI allows imaging in 3 planes, it may be useful for cryoablation of intraparenchymatous tumors.

Effects of cryoablation on short-term development of urinary fistulas in the porcine kidney.

PURPOSE To determine the effect of cryoablation on the collecting system in the porcine kidney and the possible development of pelvic injury or fistula. MATERIALS AND METHODS Six kidneys from three domestic swine were utilized. Under MRI guidance, a 3-mm cryoprobe was placed percutaneously and advanced to a point adjacent to the collecting system. The tissue then was frozen to -40 degrees C for 4 to 6 minutes to create a 2-cm iceball. At 1 week postprocedure, the kidneys were harvested and underwent gross and microscopic examination for evidence of fistula formation or renal pelvis injury. RESULTS The procedures were performed without complications, although during placement of the probe in one pig, the collecting system was inadvertently entered. The diameter of the iceballs ranged from 2.0 to 2.5 cm. On pathologic examination, five of six of the kidneys, excluding the one noted above, were found to have no gross evidence of injury or fistula formation from the collecting system. Microscopic examination of the collecting system demonstrated necrosis extending up to the mucosa but no injury to the collecting system itself. CONCLUSIONS In this animal model, no evidence of damage to the renal collecting system secondary to freezing was found. Treatment of renal tumors that are close to the collecting system may be possible without damage to the collecting system.