Investigations have been performed utilizing a tissue-specific ultrasound contrast agent (UCA) for sonographic evaluation of the lymphatic system (i.e., "lymphosonography") in a variety of animal species. Once injected directly into tissues, the UCA is rapidly picked up by lymphatic channels (LCs) draining to regional lymph nodes. Thus, the ability to inject this agent around a variety of tumors provides a novel means to sonographically identify the tumor's lymphatic drainage pathways and localize sentinel lymph nodes (SLNs).
Preliminary research using a swine model with naturally occurring melanoma has determined that lymphosonography is more accurate than lymphoscintigraphy for SLN detection. When compared to dye-guided surgery as a gold standard, the accuracy of lymphosonography is approximately 88% compared to 68% of lymphoscintigraphy. Unlike lymphoscintigraphy or the use of dyes, lymphosonography also can be utilized to characterize nodes by identifying metastases in SLNs with close correlations found between the contrast-enhanced sonography results and pathology.
Recent investigations have demonstrated the ability to not only detect and characterize SLNs with lymphosonography, but also to localize second-echelon nodes. This can be accomplished by using ultrasound to guide injections of the same UCA into previously identified SLNs which results in the detection of LCs draining from the SLN to secondary lymph nodes.
The use of lymphosonography has several potential advantages over current methods utilized to assess lymphatic drainage from tumors including the ability to non-invasively localize LCs, characterize SLNs and provide guidance during surgery. Investigations are on-going in the use of lymphosonography for a variety of applications.