Evaluation of Salivary Gland Lesions by Real Time Sonoelastography: Diagnostic Efficacy and Comparative Analysis with Conventional Sonography

Abstract

ABSTRACT Introduction: Imaging of salivary gland lesions is a major challenge for radiologists and differentiation of malignant and benign lesions is extremely important. The current modalities ultrasonography, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), despite being highly sensitive, lack the accuracy in differentiating benign and malignant lesions. Sonoelastography is a novel imaging modality that identifies elasticity of tissues. Most of the malignant lesions are harder due to desmoplastic reaction, making sonoelastography, a paramount non-invasive technique and its importance needs no further emphasis. Aim: To investigate the diagnostic efficacy of Sonoelastography in the evaluation of major salivary gland lesions and comparative analysis of its sensitivity and specificity with conventional Sonography. Materials and Methods: A total of fifty-one patients with salivary gland lesions (including inflammatory, reactive, benign and malignant) were evaluated from December 2015-June 2017 by conventional sonography and sonoelastography. The sonoelastography image was evaluated using colour coding ranging from blue (soft) through green and red (hard) and strain ratios were calculated. Then, grading was done according to the 4-point elastography score and results compared with histopathology findings. Statistical analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0. Receiver Operating Characteristic (ROC) analysis, Fisher’s-exact test and Chi-square tests were used statistically and best cut-off value of strain ratio and elastography score for predicting malignancy was determined. p-value of <0.05 was considered as statistically significant. Results: Of the 51 lesions (21 in females and 30 in males) mean age of subjects 39.3±12.9 years, 35 were located in parotid and 16 in submandibular gland; 39 being benign and 12 malignant. The diagnostic accuracy of sonography, elastography score and strain ratio was determined in comparison to pathological diagnosis. It was found that the value of elastography score alone is not significant (p=0.308) with low sensitivity and negative predictive value (41.67% and 82.93%, respectively). However, strain ratio showed statistically significant difference (p<0.0001) with high sensitivity and Negative Predictive Value (NPV) (100% each) in differentiating benign and malignant lesions. Conclusion: The parameters used in sonoelastography are strain ratio (Semi quantitative) and Elastography score (Qualitative). Strain ratio adds to the diagnostic efficacy of conventional sonography by attaining high sensitivity and NPV while Elastography score has a limited role in enhancing the diagnostic efficacy of conventional ultrasound.

Keywords

• benign
• imaging
• lesions
• malignant
• pathology