Impact of probe tip orientation and distance on collecting system injury during renal microwave ablation in a porcine model

Monday, March 6, 2023

3:18 PM – 3:27 PM

Location: Phoenix Convention Center, 221AB

Abstract Speaker(s)

Amanda R. Smolock, MD, PhD

Assistant Professor
Medical College of Wisconsin

Disclosure(s): AstraZeneca: Advisory Committee or Review Panel Member (Ongoing); Histosonics Inc: Advisor/Shareholder (Ongoing); J&J / Ethicon / NeuWave: Research Grant Recipient (Ongoing), Speaking and Teaching (Ongoing)

Author/Co-author(s)

RV

Radha Vaddavalli, PhD

Postdoctoral Fellow
Medical College of Wisconsin
VG

Venkateswara Gogineni, PhD

Assistant Professor
Medical College of Wisconsin
SW

Sarah B. White, MD, MS, FSIR

Professor
Medical College of Wisconsin

Disclosure(s):

Amanda R. Smolock, MD, PhD: AstraZeneca: Advisory Committee or Review Panel Member (Ongoing); Histosonics Inc: Advisor/Shareholder (Ongoing); J&J / Ethicon / NeuWave: Research Grant Recipient (Ongoing), Speaking and Teaching (Ongoing)

Sarah B. White, MD, MS, FSIR: Cook Inc: Consultant (Ongoing); PENUMBRA INC: Speaking and Teaching (Ongoing); TriSalus: Advisory Committee or Review Panel Member (Ongoing)

Purpose: The purpose of this study was to evaluate the effect of microwave ablation (MWA) probe tip and orientation relative to the central renal collecting system on the incidence of collecting system injury.

Materials and Methods: A single MWA probe (NeuWave PR 15, Madison, WI) was placed under ultrasound guidance into the lower pole of each kidney in 6 pigs (female, ~50kg). Perpendicular and parallel orientation relative to the collecting system was alternated and distance of tip to collecting system was varied. All ablations were performed at 65W for 5 minutes. Non-contrast CT was obtained to document probe position followed by contrast-enhanced CT to evaluate ablation zone and any complications. Kidneys with proximal ureter were fixed in formalin. Histologic assessment was made for damage to the collecting system and ureter and graded using a standard system.

Results: The median distance of probe tip to collecting system was 1.75 (0.1-3.2) cm in the parallel group and 0.85 (0.1-1.3) cm in the perpendicular group. Mean maximum probe temperature in the parallel group was 118.7 (+/- 8.5) °C and in the perpendicular group was 109.5 (+/- 6.8) °C. Ablation zones abutted the collecting system in 67% of the parallel group and 83% of the perpendicular group. Four of 12 (33%) ablations resulted in injury to the collecting system/ureter. One was in the parallel group with injury to the renal pelvis identified as mucosal epithelium attenuation and ulceration. Three were in the perpendicular group demonstrating acute injury to the ureter with ureter muscularis hemorrhage and necrosis. All injuries were seen when ablation zones abutted the collecting system/ureter. There were no findings on CT that appeared to be predictive of histological evidence of ureteral injury. A hematoma with contrast extravasation confirmed on pathology was seen in 1/12 ablations. There were no urine leaks on CT or histopathology.

Conclusion: Ablation zones that contact the collecting system/ureter, regardless of orientation of probe placement, appear to cause acute damage. However, transmural injury causing urine leak was not seen in any case. Survival studies are needed to fully elucidate the long-term significance of the findings of acute injury.