Lymph node size is an important variable in ultrasound diagnosis of
lymph node metastasis. However, the size criterion often leads to oversight of
tumor-positive lymph nodes within the range of "normal" size, such that more accurate diagnostic criteria for
lymph node metastasis are required. In this study, we show how diagnosis of
lymph node metastasis can be improved by evaluating changes in blood vessel volume and density using a novel contrast-enhanced high-frequency ultrasound (CE-HFUS) system with
Sonazoid. An MRL/MpJ-lpr/lpr (MRL/lpr) mouse model of
lymph node metastasis was used in which lymph nodes are similar in size to humans.
Metastasis via lymphatic vessels to proper axillary lymph nodes (proper ALN) was induced by injection of
tumor cells into the subiliac lymph nodes. Within 21 days of injection, significant increases in blood vessel volume and density, but no increases in the size of the proper ALNs, were observed. The increase in blood vessel density was confirmed with immunohistochemical analysis and was positively related to
tumor cell proliferation as measured using bioluminescence imaging. Together, our results showed that alterations in blood vessel volume and density precede alterations in lymph node size in the early stages of
lymph node metastasis. Detection of these changes by ultrasonography may offer new criteria for early diagnosis of
lymph node metastasis.