The clinical utility of ARFI imaging for the differential diagnosis of salivary gland tumors

Abstract

Objective Elastography is expected to be useful as an additional diagnostic aid for differentiating between benign and malignant tumors, but the diagnostic accuracy of conventional elastography is low in the salivary gland. Acoustic radiation force impulse (ARFI) imaging is a kind of elastography with a new mechanism. The purpose of this study is to clarify the clinical usefulness of ARFI imaging in distinguishing salivary gland tumors. Patients and Methods This study included patients who underwent ultrasonography and cytological or histological evaluation of salivary gland tumors at our department between July 2014 and February 2019. ARFI imaging was performed using Virtual Touch imaging (VTI), which was presented in grayscale, with dark color indicating hard. VTI images were divided into the following scores: score 1, mostly white color or white honeycomb; score 2, gray color with light parts; score 3, gray color; score 4, dark gray or black color with light parts; and score 5, dark gray or black color. The VTI images of different tumors were compared. Results Overall, 151 cases were benign tumors (87 Warthin tumors, 59 pleomorphic adenomas, 3 oncocytomas, 1 basal cell adenoma, 1 myoepithelioma) and 21 cases were malignant tumors. In the benign tumor group, 10, 56, 32, 34, and 19 VTI images were classified as score 1, 2, 3, 4, and 5, respectively, while the corresponding numbers were 0, 1, 5, 5, and 10 in the malignant group. If scores 4 and 5 were defined as malignant tumors, the sensitivity, specificity, and diagnostic accuracy for differentiating benign and malignant tumors were 76.5%, 67.6%, and 68.8%, respectively. In benign tumors, among Warthin tumors, 88.5% were included in scores 1–3, while among pleomorphic adenomas, 72.9% were included in scores 4 and 5. Among the malignant tumors, 71.4% were included in scores 4 and 5. Malignant tumors of scores 2 and 3 were located deeper site than those of scores 4 and 5. Conclusion Regarding salivary gland tumors at shallow site, AFRI imaging was considered useful technique because scores 1–3 of VTI system can be predicted benign tumors, especially Warthin tumors.