The role of elastography in course of endobronchial ultrasound in the determination of lymph node rigidity: a retrospective study

BACKGROUND: Elastography is an ultrasound technique capable of providing additional information in course of EBUS (endobronchial ultrasound): it assesses the rigidity of the tissues rather than the tissue morphology. The images show the relative difference in stiffness between the various fabrics. Two types of elastography are available: strain elastography (SE) and shear wave elastography (SWE). Strain elastography produces an image based on the movement of the tissue caused by a compression / relaxation force applied from the outside (by means of the movement of the transducer) or generated by the patient himself (breathing and/or heartbeat), this technique allows an evaluation of quality of the lesion, i.e., its relative stiffness compared to that of the other tissues present in the field of view (FOV). Shear wave elastography uses a particular thrust impulse, called the acoustic radiation force impulse, which determines the propagation of transverse or shear waves whose speed can be measured. This technique allows to obtain a quantitative evaluation of the rigidity, or to express it in the form of a numerical value. METHODS: In this study 336 lymph nodes were sampled with linear probe ultrasound to evaluate lymph node morphology and SE elastography was used to assess rigidity degree. It was evaluated the correlation between the stiffness of 336 lymph nodes by SE and the cytological finding obtained by sampling the lymph nodes subjected to EBUS/EUS-TBNA and processed in ROSE or through cell block. RESULTS: The results obtained are 181 lymph nodes (54%) blue prevalence, 104 (31%) green prevalence, 51 (15%) mixed. Out of the 336 lymph nodes sampled, 327 were diagnosed with malignant neoplasm and 9 with benign pathology. Of the 327 lymph nodes diagnosed with malignancy, 173 had blue elastography prevalence, 49 mixed prevalence, 105 green prevalence. Instead, the 9 lymph nodes diagnosed with benign disease: 2 had blue prevalence, 2 mixed prevalence and 5 green prevalence. CONCLUSIONS: Elastography can provides a better guide of the lymph node area to sample. The assessment of the colorimetric classification of the mediastinal lymph nodes must be correlated to the patient's clinical history in order to better interpret the histological results. The method requires further development studies and technological improvement as it lacks a uniform reference standard to always be used in the clinical practice of interventional pulmonology.