In response to letter to the editor from Ma et al. 2019 regarding perivascular extension of microwave ablation zone

Dear Editor,

We would like to thank Ma et al. for their interest and comments on our study describing perivascular extension of the ablation zone associated with microwave ablation.

Ma and colleagues questioned the conclusions related to some aspects of the methodology; in particular, the time between perfusion and the sampling for histological evaluation. This is an important issue. The liver samples were selected and processed within 30 min of perfusion in both the non-perfused and perfused livers. This time period is crucial to the histological results which will be obtained and is reflecting in our study the early stages of tissue injury. Processing after a longer time period of perfusion (24 h) may produce a larger ablation zone but the reduced perfusion and viability of the organ with prolonged perfusion would suggest that this will not reflect the clinical scenario, and hence is of limited value as an experimental model.

In a previous study, we demonstrated that the presence microcirculation significantly reduces the size of the MWA zone [1]. Hence, we agree that perfusion helps dissipate the heat energy from the MWA zone.

With regards to the importance of blood flow in the development of perivascular extension, this was found in both the perfused and non-perfused livers suggesting that it is not dependent on vascularity within the liver. The presence demonstrated shortly after the perfusion period would suggest that it is a primary phenomenon related to the MWA rather than a secondary phenomenon. Performing delayed evaluation will make the separation between a primary and secondary injury more complex to define and may undermine the clinical usefulness of the data.