To the Editor:
We have read with great interest a recent report published by Leen et al.1 The authors showed how contrast-enhanced intraoperative ultrasonography (CE-IOUS) could improve detection power of colorectal cancer liver metastases during surgery. For this purpose, they studied a series of 60 patients prospectively enrolled in 2 European centers. In 2004, we have, for the first time in literature, proposed the use of CE-IOUS using the same contrast agent reported by Leen etal (Sonovue, Bracco Imaging, Milan, Italy) during surgery for liver tumors, and we demonstrated its feasibility in 20 consecutive patients.2 After that, our monocentric experience has increased, and we reported the use of CE-IOUS during surgery for hepatocellular carcinoma,3 and more recently just for colorectal cancer liver metastases.4 Focusing on this last aspect, which was studied by Leen et al, it is noteworthy that our rate of modified staging by CE-IOUS alone was 21%, which is very close to the 22.8% reported by Leen et al. These similar results are demonstrating that CE-IOUS is feasible and repeatable, as it could provide information that are not strictly dependent from the operator and the equipment used. Indeed, we used for liver exploration a lower frequency probe than the one used by Leen et al. We did it because in 2002, when we started our experience, we had no dedicated technology. However, we have repeatedly demonstrated2–4 that, using a conventional convex probe commonly adopted for the percutaneous exploration, CE-IOUS is feasible and accurate, without the need of particular settings such as the pulse inversion harmonic (PIH). Furthermore, some advantages exist using lower-frequency probe: indeed, despite the lower resolution power than the higher frequency ones, lower frequency probe allows longer and stronger contrast enhancement. Longer time of exploration, stronger enhancement obtainable, and lower frequency itself permit better exploration of the deeper portions of the liver, providing for that more panoramicity than that obtainable with higher-frequency probes. Conversely, for superficial lesions, palpation of the liver is often more accurate than ultrasound itself, especially in normal or steatotic liver as they are usually in patients with colorectal cancer liver metastases. Indeed, the main target for surgeons is to find deeply located tiny lesions not visible and not palpable: the lesion shown in the figure of the report of Leen et al seems not that small, is located superficially in the caudate lobe, and therefore was well palpable and detectable. Furthermore, that lesion had no close relationship with vessels for which, as we showed, CE-IOUS could be useful in better disclosing tumor margins and relations with vessels.4 What I would like to know from the authors is how many of the new lesions they detected with CE-IOUS only were also palpable? Which were the segments where the authors found more frequently additional lesions using CE-IOUS in the way they did?
Certainly, for surgical use, high-frequency probes are anyway needed, and they should be small and stable; but these features are mainly related to their use as indispensable tools for resection guidance as we reported.5 Furthermore, adopting those convex probes used for percutaneous exploration for CE-IOUS does not represent an additional cost: indeed, every ultrasound machine is basically equipped with them. Inversely, we do not need to get special capabilities (PIH), which limits our possibility to select other ultrasound machines or upgrade those we have.
In conclusion, with an actual experience of 114 CE-IOUS performed for hepatocellular carcinoma and colorectal cancer liver metastases in one center, we would congratulate Leen et al for their nice study, which again confirms the feasibility and effectiveness of CE-IOUS during liver surgery. Furthermore, this study lets the discussion move from the real need of CE-IOUS, which was still the object of debate since there was only our monocentric experience available in the literature, to other topics such as the technical requirements for that.
Guido Torzilli, MD, PhD
Daniele Del Fabbro, MD
Angela Palmisano, MD
Matteo Donadon, MD
Marco Montorsi, MD
3rd Department of Surgery
Faculty of Medicine
University of Milan
Istituto Clinico Humanitas
Milano, Italy
guido.torzilli@unimi.it
REFERENCES
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