Reply to Letter to the editor: Evaluation of renal lesions using contrast-enhanced ultrasound

by Johannes Rübenthaler (Johannes.Ruebenthaler@med.uni-muenchen.de)

Evaluation of renal lesions using contrast-enhanced ultrasound (CEUS); a 10-year retrospective European single-centre analysis

We would like to thank Dr. Herrera and Prof. Serrano for their comments on our recent manuscript about the use of contrast-enhanced ultrasound (CEUS) for the evaluation of unclear renal lesions. We totally agree with the fact that we should always find the best imaging technique which brings the best quality to our patients. CEUS for the evaluation of renal lesions has been in clinical use for several years now and the clinical impact of this technique has been already described with an ever bigger patient sample size by Barr et al. in the US [1]. CEUS is a useful method to evaluate the microcirculation of vascularized tissue and to characterize potential malignancy. Meanwhile, since the preparation of the manuscript, the EFSUMB acknowledged this fact by recommending CEUS with the highest Grade of Recommendation (GoR A) and the second highest Level of Evidence (1b) for the evaluation of unclear renal lesions: “CEUS can be used to characterize indeterminate renal lesions (LoE 1b, GoR A). Strong Consensus (19/0/1, 100 %) [2].

First of all, similar to Barr et al., our manuscript is a retrospective study to evaluate the usefulness of CEUS for the evaluation of renal lesions with a histopathological correlation. We purposely excluded all patients in our patient cohort without a histopathological correlation to create a sub-cohort with the highest available and achievable gold-standard. We share the thoughts of Dr. Herrera and Prof. Serrano about patient selection and discussed the relatively small percentage of benign lesions in our study compared to national statistics in the discussion section of our manuscript, as biopsied lesions tend to had a more clinical likelihood of being malignant. However, since the CEUS examinations were reported at the time of the examination without knowing the final histopathological outcome, the authors believe that this bias is negligible if the reader is aware of the fact that the study deals with a selected patient cohort.

Secondly, to clarify the question about the 726 patients not having a histopathological correlation to their CEUS examination, the authors want to state that not all of these examinations were reported as benign. As described in the manuscript most of these lesions were reported as benign, thus not needing histopathological confirmation [3-5]. However, this cohort also includes patients with CEUS examinations with lesions with suggested malignancy, but the authors could not retrieve any information about the final histopathological outcome, e.g. due the fact the patients were not biopsied or operated at our institution. Therefore these patients were also excluded in our study for further analysis as these patient did not meet the inclusion criteria for this study.

Finally, regarding the question about complementary imaging studies the authors are aware of the fact that for example the Bosniak classification differs between imaging modalities and adjustments must be made between different imaging modalities to compare them to each other [6]. In the authors opinion these patients were not suitable for the current study as the emphasis of this study heavily relied on histopathology as the highest possible gold standard. Nevertheless, In an effort to contribute to the current body of research, our research group collaborated with two other german CEUS-centers and pooled parts of our study cohort that in fact have additional complementary imaging series to create a muliti-center study cohort for further analysis. Results of this analysis were already presented at the congress of the german radiological society and are currently under review for publication in an international peer-reviewed journal [7]. The authors are looking forward discussing the implications of the current study in context with these additional findings in the future.

We once more want to thank Dr. Herrera and Prof. Serrano again for their appreciation of our study and for this unique opportunity to discuss the importance of CEUS for the evaluation of unclear renal lesions. Up to date, this technique offers great potential for an easy, cost-effective and fast characterization of indeterminate renal lesions. We anticipate and truly believe that our present study and future studies will encourage other research groups to further explore the role of CEUS for non-hepatic applications.

For the authors,
Johannes Rübenthaler