Ultrasound elastography has emerged as a non-invasive tool to “palpate” the previously unpalpable deeply buried organs and has established itself as a reliable, radiation-free and a cost-effective diagnostic equipment for quantifying the degree of stiffness of various normal and pathological tissues in the body. Given the aerated nature of pulmonary parenchyma; studies on lung elastography are scarce. Very few studies examined the use of ARFI in peripheral pulmonary consolidations (PPCs) and almost all of them excluded consolidations accompanied by pleural effusion (PE). The purpose of this study was to evaluate the diagnostic performance of ultrasound (US) point shear wave elastography (pSWE) using Acoustic Radiation Force Impulse (ARFI) technology in different benign and malignant PPCs.
107 consecutive patients with PPCs who underwent sonographic examinations between April to December 2020 at the university hospital of Marburg, Germany were recruited in the study. A verbal consent was obtained from each patient to perform an ARFI study of the PPC. 20 patients (n=20) were excluded due to the following reasons: 10 patients (n=10) due to measurement’s failure, 5 patients (n=5) due to incompliance (breath holding) with invalid measurements, 5 PPCs (n=5) due to uncertain diagnosis. Finally, 87 patients (n=87) were included in the final analysis. The ARFI studies were retrospectively analyzed and correlated to the final diagnosis. All patients received a conventional lung US examination in addition to an ARFI study (11 valid measurements in meters per second (m/s) were obtained for each PPC). Atelectatic consolidations accompanied by pleural effusions (PE) were also included. The diagnosis was confirmed by means of cyto-histological examination (performed in 73/87 (83.9%) of the patients) or by means of computer tomography (CT) and or chest-X-ray in correlation to the clinical picture (a CT scan was available in 84/87 (96.6%) of the cases). A receiver operating characteristic (ROC) analysis was implemented to examine the mean ARFI velocities (MAV) for potential cut-off values between benign and malignant PPCs. The study was approved by the local ethics committee of the Philipps-university in Marburg.
The 87 patients (49 males and 38 females) had a mean age of 65±14 years (range 28-88 years). The mean body mass index (BMI) was 24.1±3.5 Kg/m2. History of smoking and chronic pulmonary disease (CPD) was present in 61% (53/87) and 36% (31/56), respectively. 55% (48/87) of the PPCs were accompanied by PE. There was 58 benign PPCs (bPPCs) and 29 malignant PPCs (mPPCs). Large consolidation’s size was suggestive of malignancy (p=0.01), the mean size of mPPCs was 6.26 ±3.12 cm and of bPPCs 4.02 ±1.98 cm. A cutoff size of 4.75 cm has a sensitivity and specificity of 65.5% and 82.5%, respectively in diagnosing mPPCs (AUC=0.729, 95% CI= 0.577-0.881). Consolidations accompanied by PE had lower MAV values and were more likely to be benign (P<0.001). Smoking history, presence of a CPD, age, gender and BMI were not associated with increased risk of malignancy in the study (p> 0.05). bPPCs demonstrated significantly lower MAV values as mPPCs (1.82±0.97 vs. 3.05±0.73 m/s) (p<0.001). Selecting 2.21 m/s as a cut-off value yielded a sensitivity and specificity of 89.7% and 75.9%, respectively in diagnosing mPPCs (AUC=0.852, 95% CI =0.773-0.931). No significant differences were found between atelectases due to benign underlying causes (AT-b, n=21) and those due to malignant underlying causes (AT-m, n=17) (p=0.33) nor between pneumonias (n=9) and all atelectases (n=38) (P=0.66). Lung infarctions and certain other chronic inflammatory/granulomatous benign consolidations (n=11) showed high MAV values comparable to those of mPPCs (p=0.42). One interesting finding was the higher stiffness of primary lung tumors (n=19, MAV= 3.33 ±0.71 m/s) vs. metastases (n=10, MAV=2.52 ±0.39 m/s) (p= 0.002). Setting 2.82 m/s as a cut-off value would have a sensitivity and specificity of 79.0% and 90.0 %, respectively in differentiating primary lung tumors from metastases (AUC=0. 847, 95% CI= 0.701-0.993).
ARFI elastography could be a good non-invasive tool in the diagnostic armamentarium of peripheral pulmonary consolidations helping in the differentiation between benign and malignant consolidations as well as between malignant consolidations of pulmonary and non-pulmonary origins (metastases). However, some degree of overlap between different disease entities does exist and the diagnosis should be made in correlation with the clinical context, larger prospective studies are needed to validate these results.