Liquid Nitrogen-Based Cryoablation in In Vivo Porcine Tissue: A Pilot Study

Abstract

Introduction: Liquid nitrogen-based cryoablation induces freezing evenly throughout the probe tip surface, resulting in larger ablation volumes and faster treatment times. The purpose of this preliminary investigation is to determine the efficacy of the liquid nitrogen-based Visica2 Cryoablation System (Sanarus Technologies, Pleasanton, CA) in in vivo porcine kidney, liver, and fibro-fatty tissue.

Methods: Ablations were performed under ultrasound guidance in 4 Yorkshire pigs. The target lesion cross-section width (W) and depth (D) were 1 cm for liver (n=8), kidney (n=4), and head-neck (n=5) and 2 cm for kidney (n=4). Expected axial length (L) of the resulting lesion is approximately 4 cm. After three-day survival, the ablated tissue was harvested and histologically analysed. The mean width and depth were compared with the target diameter using a one-sample t-test.

Results: All animals survived the procedure. For the 1 cm target, mean dimensions (L x W x D) were 3.8±1.5 x 1.7±0.3 x 1.7±0.7 for liver, 3.0±0.5 x 2.0±0.4 x 1.7±0.6 for kidney, and 3.3±0.8 x 1.8±0.4 x 1.8±0.4 for head-neck. Mean width and depth were significantly greater than desired dimension. For the 2 cm target, mean dimensions were 3.2±0.5 x 3.1±0.8 x 1.9±0.7. Mean width and depth were not significantly different to desired target.

Conclusion: Our preliminary results show that the Visica2 liquid nitrogen-based cryoablation system can efficiently and reproducibly create ablation volumes in liver, kidney, and fibro-fatty tissue within 4 minutes and 12 minutes for 1cm and 2cm targeted diameters, respectively. Further investigation is necessary to determine the optimal freeze-thaw-freeze protocol for larger ablation volumes.<br />.

Keywords: Cryotherapy; Liver cancer; Minimal invasive surgery; cryoablation; kidney cancer.

Figure 1

Sanarus ICE Probe Inserted Percutaneously into an Animal under Ultrasound Guidance

Figure 2

A-B. Right and left liver lobes with well demarcated ablation areas. C. Kidney upper and lower pole ablated areas with marked hemorrhage in perinephric fat. D. Head and neck fibro-fatty and muscular tissue with a well circumscribed ablated area

Figure 3

A. Periphery of an ablated zone demonstrating from left to right: viable liver, inflammatory response, hemorrhagic necrosis, nuclear dust and necrotic ablated liver (H and E stain). B. NADH staining showing viable liver on the left and necrotic ablated liver on the right. C. High power of viable liver on the left followed by bile duct reaction, lymphocytes, plasma cells, eosinophils, and hemorrhagic necrosis (H and E stain). D. High power showing a rim of nuclear dust and coagulative necrosis on the right (H and E stain)

Figure 4

A. Low power section showing from left to right viable renal parenchyma followed by a congested area with tubular necrosis, a rim of nuclear dust and coagulative necrosis (H and E stain). B. Scant inflammation between viable renal parenchyma (left) and necrosis (right) (H and E stain). C. Necrotic proximal renal tubules adjacent to distal tubules showing luminal proteinaceous material (H and E stain). D. NADH staining demarcating viable (left) from necrotic (right) parenchyma

Figure 5

A. Head and neck soft tissue and muscle showing viable tissue (left), marked inflammatory reaction (middle) and necrotic tissue (right) (H and E stain). B. Organized viable (left) and necrotic (right) muscle fibers (H and E stain). C. Marked inflammatory infiltrate comprised of neutrophils, plasma cells and myofibroblasts, adjacent to necrotic muscle bundles (right lower) (H and E stain). D. NADH staining showing positive viable muscle fibers (left) and negative necrotic tissue (right)