The current value of quantitative shear wave sonoelastography in parotid gland tumors

Abstract

Background: The preoperative differentiation between salivary gland tumor entities using computed tomography, magnetic resonance imaging (MRI) and ultrasound (US) is still limited. Biopsies are often regarded as indispensable for properly characterizing these various lesions. The aim of this study was to analyze the value of acoustic radiation force impulse (ARFI) sonoelastography as an US differentiation tool when examining parotid gland (PG) lesions.

Methods: We included 104 patients with PG masses in this study, employing two different US devices using quantitative ARFI-sonoelastography (Siemens Acuson-S3000, n=59; Siemens Acuson-Sequoia, n=45). The ability of sonoelastographic measurements to differentiate between different neoplasms was compared and analyzed for both US machines.

Results: Quantitative shear wave sonoelastography is limited in its ability to reliably differentiate between tumor entities of the PG as a stand-alone parameter. Measurement results were unsystematically distributed and not transferable between the two US devices. A significant differentiation of benign and malignant lesions was not possible with either US machine (S3000: P=0.770, Sequoia: P=0.382). A differentiation between pleomorphic adenomas (PA) and Warthin tumors was only possible with the Acuson S3000 system (P=0.001, Spearman-Rho =0.492, sensitivity 73.9%, specificity 65.0%).

Conclusions: A reliable identification and differentiation of PG tumors as well as clinical treatment decisions cannot be made with the sole use of ARFI-sonoelastography. The results emphasize the device-dependence and high error-proneness of this US technique when examining lesions of the PG.

Keywords: Ultrasound (US); acoustic radiation force impulse (ARFI); parotid gland (PG); salivary gland tumors; sonoelastography.

Figure 1

Ultrasonography in parotid gland tumors, using either the Acuson S3000 (A-C) or the Acuson Sequoia (D-F) ultrasound system. (A) B-mode image of the right PG, depicting a mass within the parenchyma as a hypoechoic, rounded and quite homogeneous structure with defined margins. The histopathological examination subsequently identified this lesion as a pleomorphic adenoma. (B) Quantitative ARFI (Acoustic Radiation Force Impulse) shear wave elastography (VTIQ: Virtual Touch Imaging and Quantification) measurement of the lesion depicted in (A). The quadrangular region of interest (ROI) in which SWVs were obtained was positioned to cover the tumor. After the record was taken, in this case ten different measurement values were determined exclusively within the tumorous area. SWVs are additionally shown as color-coded signals (red: high velocities; green: low velocities). (C) Quality assurance of the obtained elastographic record revealing a high and homogeneous measurement quality throughout (green). (D) B-mode image of a second right PG in a different patient. The hypoechoic lesion here exhibits well-defined boundaries, a polycyclic shape and a slightly heterogeneous interior, also representing a pleomorphic adenoma. (E) Quantitative ARFI-2D-shear wave elastography of the mass depicted in (D). The Sequoia software uses a circular ROI within which SWVs were averaged automatically. Velocities are additionally shown as color-coded signals (red: high velocities; green: intermediate velocities; blue: low velocities). (F) Elastographic quality-assessment of the obtained image. Besides the color-coded representation, the system software automatically calculated and displayed the standard deviation (Std-Abw.) of the obtained measurement values. All parameters revealed a consistent high and homogeneous image quality. rPG, right parotid gland; MM, masseter muscle; Mand, mandible; V, retromandibular vein; MSCM, sternocleidomastoid muscle; SWV, shear wave velocity.

Figure 2

Receiver operating characteristic (ROC) curves for both ultrasound (US) devices in specific attempts at tumor differentiation. The accuracy of shear wave velocity (SWV)-values to distinguish specific tumors from one another is displayed in each image. The left column illustrates the results obtained with the Acuson S3000 system (A,C,E,G,I), the right column those obtained with the Acuson Sequoia (B,D,F,H,J). The course of the curve near the diagonal line indicates a random distribution of the measured values independent of the histopathological nature of the tumors compared. (A,B) Velocity value distribution comparing benign with malignant PG lesions. (C,D) Velocity value distribution comparing benign masses except PA with malignant lesions. (E,F) Velocity value distribution comparing PA with all other benign lesions except PA. (G,H) Velocity value distribution comparing PA with malignant lesions. (I,J) Velocity value distribution comparing PA and WT. Taken together, we could only detect significant results in the sonoelastographic differentiation of PA from WT (P=0.000) and the differentiation of PA from BENwoPA (P=0.001) using the S3000. With the Sequoia, we could not detect any significant results. PG, parotid gland; PA, pleomorphic adenomas; WT, Warthin tumors; BENwoPA, benign tumors except PA; BEN, benign tumors; MAL, malignant tumors.

Figure 3

Scatter plots illustrating the correlation of shear wave velocity (SWV-)values and tumor volumes in benign parotid gland (PG) neoplasms (Acuson S3000). A weak, but negative correlation of the recorded the SWV-values and the tumor volume of benign PG tumors was found when the Acuson S3000 US device was used. The wide range of SWV-values for similar tumor volumes is remarkable. The data for the Sequoia are not shown as no significant differences were observed.

Figure 4

Illustration of shear wave velocity (SWV-)values obtained from different tumors of the parotid gland. The recorded values show a high degree of variation even within matching tumor entities, preventing a reliable differentiation from one another. The sizes of ellipses do not reflect the number of tumors. (A) SWV-values obtained with the Acuson S3000 system and (B) with the Acuson Sequoia system.