The primary application of contrast ultrasound is to differentiate benign vs. malignant hepatic nodules or mass lesions. As we all know, non-contrast enhanced ultrasound does a poor job at determining if an hepatic nodule is malignant or benign. Ultrasound contrast promises to increase the specificity of ultrasound in making this differentiation.
Recently, several articles were published about ultrasound contrast in veterinary medcicine. Contrast clearly has potential in veterinary medicine but these articles fail to inform the reader about significant issues related to contrast harmonic ultrasound imaging.
The issues they don't tell you about in the articles
Issue #1: You probably cant buy contrast even if your tried: In October 2007, the FDA mandated a 'black box' warning on the commercial contrast agents Optison and Definity which resulted in a substantial decrease in the use of these agents. Recently, the black box warning was revised and the use of the contrast agents is on the rise. Nonetheless, these agents are difficult to acquire. At our institution, we are part of a clinical trial using a contrast agent that is not commercially available. Prior to starting this study we were unable to buy ultrasound contrast.
Issue #2: Interpretation of these studies is not straightforward: When we did our first studies we were left scratching our collective heads. Did we inject enough? Was that all? What the heck does that mean? Was the machine set properly? We soon learned that the contrast has a very short life span and improper machine settings can complicate interpretation. There is definitely a learning curve with these agents that they don't tell you about in the journal articles.
Issue #3: You will probably need a new machine to make these agents work for you. Remember, you must have a scanning probe of the proper frequency that is equipped with the proper harmonic capability. Any old ultrasound machine won't do.
Issue #4: If you can get it, contrast is expensive: Unless you are part of a research project and you get your contrast for free, contrast is expensive. Given the cost of the contrast (if you can get it) and time to perform the procedure, you can probably go to surgery and biopsy any nodules that are identified in the liver. For many owners, contrast enhanced ultrasound is not a practical (financial) option.
A quick summary of the current research
The most pertinent clinical article, as far as we are concerned, was published in the January 2009 JAVMA.
In this article the investigators found that splenic hematomas and hemangiosarcomas cannot be differentiated with the use of contrast ultrasound. This is similar to the findings in our research study. For now, it seems that we still need histopathology to determine if a splenic mass is a tumor or if it is benign.
However, contrast ultrasound was worthwhile in the workup of splenic masses. These investigators were able to differentiate with 100% specificity whether a liver nodule was benign or malignant. Benign nodules became less conspicuous and malignant nodules became more conspicuous after contrast was administered. That is very cool but the usefulness of contrast ultrasound does not stop there.
In our research study, we have identified cases where the noncontrast enhanced ultrasound evaluation of the liver was completely normal. In these dogs no nodules were identified prior to the administration of contrast. After enhancement, we identified nodules with a metastatic enhancement pattern. Although we are still waiting for the final results of our study, presumably, these patients had metastatic liver nodules that would have been overlooked had we not administered contrast. The positive clinical implications of this finding cannot be overstated.
Our current recommendations
Currently, we recommend contrast harmonic evaluation of the evaluation of splenic mass lesions*. In these cases, the risk benefit cost analysis for owners is as follows:
- If the survey ultrasound of the liver is normal and additional mass lesions are identified and characterized as metastatic the contrast procedure was invaluable and the owner can decide if they will pursue surgery knowing that the prognosis is worse than if metastatic disease was not present.
- If the survey ultrasound of the liver identified hepatic nodules, the contrast procedure will (hopefully) be able to determine if these masses are benign or malignant. Again, the contrast is invaluable and the owners can decide on surgery knowing that the prognosis is worse than if metastatic disease was not present.
- Finally, if the survey hepatic ultrasound is negative and no additional nodules are identified with contrast, metastatic hepatic disease is presumably absent and the owners can move forward with surgery knowing they have a better long term prognosis than if nodules were identified.
Bottom line: we currently recommend the use of contrast harmonic ultrasound in the evaluation of canine splenic masses to help identiy hepatic metastatic lesions and differentiate any hepatic lesions as benign vs. malignant. Lets just hope our research project never ends or contrast agents become more available.
*In patients with hemoabdomen, contrast may or may not be indicated. Some of our radiologists believe that because these patients need to go to surgery anyway the cost and time involved with administration is not justified given our current understanding of these agents. Other radiologists believe that contrast is still indicated because many owners would like this information and it may still help with their decision of surgery vs. euthanasia.