Department of Radiology, Seoul National University Hospital
Ultrasound （US） is often the first-line imaging modality in the evaluation of the renal masses. If the findings of a renal mass do not meet all of US criteria of a simple cyst, it should be characterized further. Usually characterization of indeterminate renal masses is well done with CT or MRI, but sometimes it is inconclusive. In thoses cases and in patients to whom radiation exposure or use of iodine or gadolinium contrast agents is undesirable, contrast-enhanced US （CEUS） may be a valuable modality to evaluate those indeterminate renal masses. CEUS may replace CECT or CEMRI if the patient has marginal or poor renal function, hypersensitivity to iodine contrast agent, or fear of radiation exposure. CEUS has long history in the history of US in medicine but drew attention only recently. With the first generation microbubble agents several studies showed added value of CEUS as compared to the conventional color Doppler US （CDUS） or power Doppler US （PDUS）. We have done a study using a first generation agent in 13 patients, and reported that CEUS provided better visualization of tumor vascularity in indeterminate cystic renal lesions than other imaging modalities. The most important limitation of the first generation agent was that it could not provide an enough duration of contrast enhancing effect. With introduction of the second generation microbubble agents with better stability and duration of contrast effect, CEUS examination became a practical alternative of CECT or CEMRI in evaluation of indeterminate renal masses. We do not think that CEUS will be used routinely in US examination of renal masses like contrast enhancement is routine in CT of renal masses. However, we are sure that CEUS will be a valuable imaging technique if it is used in well selected cases of indeterminate renal masses. In evaluating an indeterminate renal mass, CEUS may show findings that were not seen at other imaging or confirm findings equivocal at other imaging studies. Results of CEUS can be analyzed qualitatively as to the presence or absence of enhancement, vascular pattern and heterogeneity etc. Quantitative analysis can be done on peak intensity, time to peak, and rate of wash-in and wash-out, etc. There has been reports on the value of CEUS in differentiation of benign and malignant renal masses and prediction of histologic subtypes of renal cell carcinomas.