Ultrasonography methods for predicting malignancy in canine mammary tumors

Abstract

The aim of this study was to evaluate and compare the efficacy of B-mode, Doppler, contrast-enhanced ultrasonography (CEUS), and Acoustic Radiation Force Impulse (ARFI) elastography in predicting malignancy in canine mammary masses. This was a prospective cohort study from 2014 to 2016, which included 153 bitches with one or more mammary masses. A total of 300 masses were evaluated by ultrasonography (B-mode, Doppler, CEUS, and ARFI) and subsequently classified as benign or malignant by histopathology. Each ultrasound parameters studied were compared between benign and malignant masses by Chi-square or Student tests and differences were considered significant when P < 0.01. For the variables that proved significant differences were estimated the cut-off point, sensitivity, specificity, accuracy, and area under curve (AUC) by receiver-operating characteristic curve (ROC) analysis in a logistic regression model using histopathological classification as reference, to assess and compare diagnostic performance of each technique. Out of 300 mammary masses evaluated 246 were classified as malignant and 54 as benign. B-mode measurements showed sensitivity 67.9%, and specificity 67.6% as malignancy predictors on canine mammary masses; Doppler indexes systolic (>21.2 m/s) and diastolic velocity (>4.8 m/s) sensitivity 79.2% and specificity 70.8%; CEUS wash-out time (<80.5 s) sensitivity 80.2% and specificity 16.7%; and ARFI elastography shear velocity (SWV > 2.57 m/s) sensitivity 94.7% and specificity 97.2% In conclusion B-mode and Doppler ultrasound evaluations may assist in malignancy prediction of canine mammary masses with moderate sensitivity and specificity, already the SWV was an great accurate predictor. Therefore, ARFI elastography exam inclusion in veterinary clinic oncology and research is highly recommended, since it allows fast, non-invasive, and complication-free malignancy prediction of canine mammary masses.

Fig 1. Receiver-operating characteristic curve comparing predictive sensitivity (%) and specificity (100-%) of different ultrasonography methods in determining malignancy in canine mammary masses using histopathological classification as a reference.

Different letters indicate significant difference.

Fig 2. B-mode and Doppler ultrasonographic image of a canine mammary tumor—Solid carcinoma in female dog.

B-mode image of mammary tumor (arrows) with presence of intratumoral calcification (cl) (A). Spectral Doppler ultrasonographic image of mass (arrows) with tumoral neovascularization and waveforms highlighting blood flow with indicated values of malignancy (high resistance and values on the right hand side) (B).

Fig 3. Contrast-enhanced ultrasonography (CEUS) image of a canine mammary tumor—Solid carcinoma in female dog.

Color Doppler in mammary neoplasm (A) highlighting the presence of neovascularization in the tumor. The contrasted technique was applied to evaluate capillarization characteristics of the tumor: (B)—absence of contrast, (C) peak enhancement and diffuse enhancement, and (D) contrast wash-out. Time acquisition after contrast medium injection is located at the bottom of the right side of the images (B, C and D).

Fig 4. Acoustic radiation force impulse (ARFI) elastography image showing stiffness characteristics in a canine mammary tumor—Carcinoma in a mixed tumor in female dog.

High quality image map (arrows) of VTIQ shows a homogeneous green picture of the lesion (white dotted line delimiting the neoplasm) (A). In VTIQ shear wave velocity mode (B), SWV values in the lesion (white dotted line delimiting the neoplasm) were measured and repeated five times. In elastogram (VTIQ qualitative—B), the image of the neoplasm (arrows) is heterogenous and not deformable, with rigid tissue (reddened areas in the central region) and with soft tissue (greenish areas in the peripheral region).

Fig 5

Image of the acoustic radiation force impulse (ARFI) elastography, which shows the values of shear velocity (right bottom corner) of images in the mammary tumors (arrows): A)–mixed benign tumor—shear velocity of 1.17 m/s; B) mixed benign tumor—shear velocity of 0.64 m/s; C) carcinoma in a mixed tumor (grade III)—shear velocity of 8.04 m/s; and D) carcinoma in a mixed tumor (grade II)—shear velocity of 2.84 m/s.