Analysis of endoscopic ultrasound elastography used for characterisation and differentiation of benign and malignant lymph nodes

Purpose: Ultrasound elastography is a new imaging procedure which allows the reconstruction of elasticity distribution by characterising the difference of hardness between pathological and normal tissue. Materials and Methods: The aim of our study was to apply real-time elastography during endoscopic ultrasound (EUS) examinations and to consequently characterise benign versus malignant lymph nodes. The pattern of real-time EUS elastography images was compared with the conventional EUS aspects of lymph nodes and with the final diagnosis obtained by EUS-FNA cytology analysis and/or by surgical pathology. Results: Patients diagnosed by EUS with cervical, mediastinal or abdominal lymph nodes were prospectively included, with a total number of 42 lymph nodes examined by EUS elastography. By using a qualitative pattern analysis, we were able to differentiate between benign and malignant lymph nodes with a high sensitivity, specificity and accuracy (91.7%, 94.4% and 92.86%, respectively), based on five pre-defined patterns obtained on EUS elastography. A quantitative analysis based on histograms of the EUS elastography images also allowed an excellent discrimination between benign and malignant lymph nodes. Based on separate RGB channel histogram values, an "elasticity ratio" was further defined and yielded a sensitivity, specificity and accuracy for the differential diagnosis of 95.8%, 94.4% and 95.2% respectively, based on a cut-off level of 0.84. Conclusion: EUS elastography is a promising method which allows characterisation and differentiation of benign and malignant lymph nodes with a high sensitivity, specificity and accuracy, offering complementary information added to conventional EUS imaging.