Microwave liver ablation: influence of hepatic vein size on heat-sink effect in a porcine model.
OBJECTIVE
To determine influence of hepatic vein size on perfusion-mediated attenuation in adjacent microwave thermal ablation.


METHODS
With approval of the institutional animal research committee, seven Yorkshire pigs underwent percutaneous (n = 2) or open (n = 5) microwave liver ablation under general anesthesia. In each, multiple ultrasound-guided, nonoverlapping thermal lesions were created within 1 cm of hepatic veins in a 5-10-minute ablation at 45 W. After euthanasia, the liver was harvested and sectioned at 0.5-cm intervals and the degree of perivascular coagulation attenuation was graded on histopathologic analysis. Correlation between venous size (small, < or =3 mm; medium, 3-6 mm; and large, >6 mm) and attenuation grade was performed with use of the Spearman rank test.


RESULTS
In 63 of 103 sections (61%)--29 of 37 (78%) small, 27 of 48 (56%) medium, and seven of 18 (39%) large veins--the thermal injury extended to the vein wall around the entire circumference of the coagulation front without distortion of the ablation margin. In 40 of 103 sections (38.9%), varying degrees of concave distortion of perivenous ablation margins were noted, with significant correlation between vein size and heat-sink extent (P < .01). However, thermal injury extended to the vascular wall in all sections without complete circumferential sparing of liver tissue. Around two thrombosed veins, thermal lesions encased the vessels, producing paradoxically convex ablation margins.


CONCLUSIONS
Although the heat-sink effect was significantly dependent on hepatic vein size, the majority of pathologic sections exhibited no or minimal effect. Further study is required to assess clinical implications.
Yu
Nam C
NC
Department of Radiology, David Geffen School of Medicine, University of California-Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA.
Raman
Steven S
SS
Kim
Young Jun
YJ
Lassman
Charles
C
Chang
Xinlian
X
Lu
David S K
DS
D000818:Animals; D017115:Catheter Ablation / Q000009:adverse effects / Q000379:methods*; D006503:Hepatic Veins / Q000473:pathology* / Q000503:physiopathology; D007036:Hypothermia, Induced / Q000009:adverse effects / Q000379:methods*; D008099:Liver / Q000098:blood supply* / Q000473:pathology*; D008102:Liver Circulation; D008872:Microwaves; D023421:Models, Animal; D013552:Swine; D018084:Ultrasonography, Interventional