Sentinel lymph nodes in a swine model with melanoma: contrast-enhanced lymphatic US

Abstract

Purpose: To determine if lymphatic channels and sentinel lymph nodes (SLNs) with and without metastases can be detected with lymphatic ultrasonography (US) after peritumoral injection of a US contrast agent and to determine if lymphatic US can be used to assess SLNs for the presence of metastatic infiltration.

Materials and methods: Six swine with 17 melanomas were evaluated. Conventional gray-scale, color flow, and gray-scale phase-inversion harmonic US examinations were performed. A US contrast agent was administered in four sites around each melanoma (1-mL total dose). Lymphoscintigraphy was followed by injection of a blue dye and then dissection. SLNs identified at lymphatic US were characterized by two readers in consensus as normal or as having metastases; results were compared with histologic findings. Statistical analyses included the sign test and the kappa statistic.

Results: Lymphatic US depicted 28 SLNs, while lymphoscintigraphy depicted 27 "hot spots" suspected of representing SLNs (including two false-positive findings). Dissection after blue dye injection helped identify 31 SLNs. There were no false-positive US findings for SLN detection. Five of six nodes not seen with lymphoscintigraphy were detected with lymphatic US. The accuracy of SLN detection was 90% (28 of 31) for lymphatic US and 81% (25 of 31) for lymphoscintigraphy (P =.29). Lymphatic US correctly depicted metastases in 19 of 20 SLNs, and five of the eight normal SLNs were correctly characterized, with an accuracy of 86% (kappa = 0.62).

Conclusion: Detection of SLNs with lymphatic US compared favorably with that at lymphoscintigraphy. Lymphatic US can depict metastases within the SLN, which was not possible with lymphoscintigraphy.