Differentiation of Metastatic and Non-Metastatic Mesenteric Lymph Nodes by Strain Elastography in Surgical Specimens.

Purpose: To investigate if strain elastography could differentiate between metastatic and non-metastatic mesenteric lymph nodes ex-vivo. Materials and Methods: 90 mesenteric lymph nodes were examined shortly after resection from 25 patients including 17 patients with colorectal cancer and 8 patients with Crohn's disease. Ultrasound-based strain elastography was performed with a linear probe. Tissue hardness in lymph nodes was assessed using visual scales and measuring the strain ratio. B-mode characteristics were also recorded. Pathological diagnosis with grading of fibrosis served as the reference standard. Results: 20 lymph nodes were metastatic and 70 lymph nodes were non-metastatic. The strain ratios of metastatic and non-metastatic lymph nodes were significantly different (1.83 vs. 1.42, p = 0.021). The VAS scale (0-100) for tissue hardness gave higher mean values for metastatic than non-metastatic nodes, but the difference was not significant (65.5 vs. 55.0, p = 0.055). There was no difference between lymph nodes in Crohn's and non-metastatic cancer specimens. The metastatic lymph nodes were significantly more fibrotic than the non-metastatic lymph nodes by the ordinal fibrosis score (0-3). In an ROC analysis, quantitative strain imaging was not superior to the measurement of the short-axis diameter of lymph nodes in differentiating metastatic from non-metastatic mesenteric lymph nodes ex-vivo. Conclusion: Strain elastography is correlated to fibrosis in lymph nodes and a significant difference was observed on a group level using the strain ratio. Due to measurement overlap, individual mesenteric lymph nodes could not be identified accurately as metastatic or not in this ex-vivo model by strain imaging alone.