Intermittent Pringle maneuver may be beneficial for radiofrequency ablations in situations with tumor-vessel proximity.

BACKGROUND: Radiofrequency ablation (RFA) represents a treatment option for non-resectable liver malignancies. Larger ablations can be achieved with a temporary hepatic inflow occlusion (Pringle maneuver - PM). However, a PM can induce dehydration and carbonization of the target tissue. The objective of this study was to evaluate the impact of an intermittent PM on the ablation size. METHODS: Twenty-five multipolar RFAs were performed in porcine livers ex vivo. A perfused glass tube was used to simulate a natural vessel. The following five test series (each n=5) were conducted: (1) continuous PM, (2-4) intermittent PM, and (5) no PM. Ablations were cut into half. Ablation area, minimal radius, and maximal radius were compared. RESULTS: No change in complete ablation size could be measured between the test series (p>0.05). A small rim of native liver tissue was observed around the glass tube in the test series without PM. A significant increase of ablation area could be measured on the margin of the ablations with an intermittent PM, starting without hepatic inflow occlusion (p<0.05). CONCLUSION: An intermittent PM did not lead to smaller ablations compared to a continuous or no PM ex vivo. Furthermore, an intermittent PM can increase the ablation area when initial hepatic inflow is succeeded by a PM.

Comparison of bipolar radiofrequency ablation zones in an in vivo porcine model: Correlation of histology and gross pathological findings.

BACKGROUND: Continuing research ex vivo and in vivo with animal models is performed to advance the oncological safety of radiofrequency ablation (RFA) of liver tumors. In these experiments, frequently imaging modalities (e.g. MRI or CT) or macro-morphological measurements are used to determine the full extent of the different ablation zones inside of RFA lesions. However, no systematic study has been performed so far, which verified the accuracy of the macro-morphological findings. Therefore, the present study aimed to correlate histological and gross pathological findings of bipolar radiofrequency ablation zones of porcine livers with regard to cell viability in vivo. METHODS: Bipolar RFA was performed in the liver of anaesthetized female domestic pigs under CT-guidance using an internally cooled 20 mm RFA applicator. Afterwards RFA cross sections of the liver were made in a perpendicular orientation to the applicator. Ablation zones were initially documented by photography and thereafter prepared for histological analysis. Latter was based on HE-staining and NADH-diaphorase cell viability staining. Micro- and macro-morphological sections were digitally analyzed along the cross-section area for statistical correlation. RESULTS: Three different RF ablation zones could be differentiated. A central zone showing no cell viability (white zone) was surrounded by a red zone. The red zone could be divided into an inner zone of viable and non-viable cells (red zone 1), followed by a zone of edema with mostly viable cells (red zone 2).Micro- and macro-morphological data showed a strong correlation for the white zone (r = 0.95, p < 0.01), the red zone 1 (r = 0.85, p < 0.01), and the red zone 2 (r = 0.89, p < 0.01). CONCLUSION: White zone and red zone could clearly be distinguished in gross pathology and histology after bipolar RFA of porcine liver tissue in vivo. The red zone could be differentiated into an inner zone of viable and non-viable cells and an outer zone with high cell viability and intercellular edema. A strong correlation of micro- and macro-morphology could be shown for all three ablation zones. With this knowledge, gross pathological examination can be used as a reliable indicator of lethally damaged tissue in bipolar RFA of in vivo porcine liver.

Value or waste: Perfusion imaging following radiofrequency ablation - early experience.

BACKGROUND: Radiofrequency ablation (RFA) is an evolving technique in treatment of hepatic malignant tumors. By heating local tissue it leads to coagulative necrotic areas around the ablation probe. Temperature falls with increasing distance to the probe, risking incomplete necrosis at the margins of the RFA-induced lesion. Therefore, immediate non-invasive and precise detection of incomplete ablation is necessary for early enlargement of the ablation if needed. OBJECTIVES: This in vivo pig study compares early experiences of immediate post-interventional computed tomography (CT) perfusion volume analysis to macroscopic and CT image evaluation in healthy pig liver. MATERIAL AND METHODS: RFA was performed in vivo in healthy pig livers. Different CT perfusion algorithms (Maximum slope analysis and Patlak plot) were used to quantify three different perfusion parameters. Data points were acquired from rectangular grids. These grids were semiautomatically overlayed to macroscopic images documented after liver explantation. Each data point was visually assigned to zones defined as "inner" and "outer necrotic zone", "margin" or "vital tissue". RESULTS: Significant differences between necrotic zones and vital tissue are shown for equivalent blood volume (p <  0.0001), arterial flow (p <  0.01) and flow extraction product (p <  0.001). Looking at equivalent blood volume and flow extraction product, there were also significant differences (EquivBV: p <  0.0001, FE: p <  0.001) between margins, necrotic and vital areas. CONCLUSIONS: In a porcine model these early results could show that all of the used CT perfusion parameters allowed discrimination of necrosis from vital tissue after RFA at high levels of significance. In addition, the parameters EquivBV and FE that give an estimate of the tissue blood volume and the permeability, were able to precisely discern different zones also seen macroscopically. From this data CT perfusion analysis could be precise tool for measurement and visualization of ablated liver lesions and for immediate detection of incomplete ablation areas.