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Are Metastases Really Hypovascular in the Arterial Phase?

The Perspective Based on Contrast-Enhanced Ultrasonography

Department of Medical Imaging, Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada (J.M.-L., H.-J.J., T.K.K., S.R.W.); Department of Imaging Research, Sunnybrook Health Sciences Center, Toronto, Ontario, Canada (P.N.B.); and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada (P.N.B.). Dr Murphy-Lavallee is currently with the Department of Radiology, University of Montreal Hospital Center, Montreal, Quebec, Canada.

Address correspondence to Stephanie R. Wilson, MD, Department of Diagnostic Imaging, Foothills Medical Center, 1403 29th St, NW, Calgary, AB T2N 2T9, Canada. E-mail: stephanie.wilson{at}calgaryhealthregion.ca

Objective. The purpose of this study was to describe enhancement and vascularity characteristics of liver metastases on real-time low-mechanical index contrast-enhanced ultrasonography. Methods. This retrospective study was approved for chart review by our Research Ethics Board. Informed consent was waived. Fifty metastases (colorectal [n = 28], neuroendocrine [n = 6], pancreatic [n = 6], melanoma [n = 3], and other [n = 7]) in 50 patients (38–84 years, 24 male and 26 female) were analyzed. Contrast-enhanced ultrasonography was performed after intravenous injection of a microbubble contrast agent. Two radiologists independently reviewed digital cine clips and static images for the arterial phase intensity and pattern of enhancement and the presence of dysmorphic vessels. Observations on wash-out included its presence and completeness. Disagreement was resolved by consensus. The interval to peak arterial enhancement and beginning of wash-out were determined. Reader agreement was estimated with the statistic. Results. All but 6 metastases (44/50 [88%]) showed arterial hypervascularity, with dysmorphic vessels in 21 (42%) of 50. The pattern of enhancement was rim in 21 (42%) of 50 and diffuse in 29 (58%) of 50. The time to peak arterial enhancement ranged from 8 to 27 seconds (mean, 15.1 seconds), and the beginning of wash-out ranged from 13 to 50 seconds (mean, 25.2 seconds). Although a thin margin of residual enhancement was seen in 27 (54%) of 50 lesions in the early wash-out phase, all lesions (50/50) showed uniform complete wash-out in the portal phase. Conclusions. Contrary to popular belief based on computed tomography and magnetic resonance imaging studies, most hepatic metastases, including those thought to be hypovascular, show transient arterial hypervascularity on contrast-enhanced ultrasonography, followed by rapid and complete wash-out initiated within the conventional arterial phase.

Key Words: contrast agent • liver neoplasms • metastases • microbubbles • ultrasonography

Abbreviations: CEUS, contrast-enhanced ultrasonography • CT, computed tomography • MI, mechanical index • MR, magnetic resonance

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