Contrast-enhanced ultrasound in the detection and characterization of liver tumors

Abstract

Contrast-enhanced ultrasound (CEUS) has unique advantages over contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) in the characterization of hepatic tumors. These include the capability of real-time dynamic imaging depicting the enhancement pattern of tumors regardless of its rapidity, purely intravascular properties of the microbubble contrast agents more consistently demonstrating washout of malignancy, and capability of repetitive observation of tumor vascularity with multiple injections of microbubbles with an excellent safety profile and no nephrotoxicity. For an indeterminate mass detected on an ultrasound scan, an immediate benign diagnosis reduces the necessity of costly further imaging as well as patients' anxiety and an immediate malignant diagnosis prompts the proper work-up and management. CEUS is often served as a problem-solving tool for indeterminate lesions on prior CT or MRI scans, obviating further invasive steps. CEUS offers excellent visualization of peripheral nodular enhancement in even flash-filling or very slow-filling hemangiomas. Careful observation of early arterial filling pattern is helpful in the differentiation of focal nodular hyperplasia versus adenoma. Hepatocellular carcinoma is typically characterized by arterial hypervascularity and often late, partial washout. Metastasis shows brief arterial hypervascularity and complete rapid washout, which can improve its detection during a portal phase survey. The washout phenomenon of malignant tumors in general is useful to differentiate them from benign lesions.

Figure 1

A 37-year-old female with a giant hemangioma. A contrast-enhanced sonogram shows a mass with peripheral nodular enhancement (arrows) on the arterial phase (A) and gradual centripetal filling-in of enhancement (arrows) on the portal venous phase (B).

Figure 2

A 37-year-old female with a small fast-filling hemangioma. Serial contrast-enhanced sonograms at (A) 6 s, (B) 7 s and (C) 8 s show peripheral nodular enhancement with rapid filling-in of the nodule (arrowheads).

Figure 3

A 45-year-old female with hepatic adenoma. Contrast-enhanced sonograms. The mass shows tumor vessels initiating from the periphery (arrows in (A)) at 6 s (A) with centripetal filling of intratumoral enhancement at 7 s delay (B).

Figure 4

A 37-year-old female with FNH. (A) Contrast-enhanced sonogram at 8 s delay shows a mass (arrows) with central stellate arteries (arrowhead). (B) At 11 s delay, note the centrifugal progression of enhancement of the mass (arrows).

Figure 5

A 74-year-old female with HCC. (A) Contrast-enhanced sonogram at 24 s delay shows hypervascularity of the nodule (arrows). (B) Late washout of the mass typical of HCC is seen at 169 s delay (arrows).

Figure 6

A 39-year-old male with a regenerative nodule. (A) Oblique sonogram shows a well-defined hyperechoic nodule (arrows). (B) Contrast-enhanced sonogram at 13 s delay shows transient arterial hypovascularity of the nodule (arrows). (C) The nodule is isoechoic to surrounding liver parenchyma in the portal phase.

Figure 7

An 82-year-old male with cholangiocarcinoma. (A) Arterial phase CT scan shows a large mass (arrows) with irregular peripheral enhancement. (B) Three-minute delay phase CT scan shows progression of enhancement within the mass (arrows). (C) Contrast-enhanced sonogram at 19 s delay shows hypervascularity of the mass (arrows). (D) Contrast-enhanced sonogram at 34 s delay shows early complete washout of enhancement of the mass (arrows), discordant with the CT scan (B).

Figure 8

A 57-year-old male with metastasis from colon cancer. Contrast-enhanced sonogram at (A) 17 s and (B) 36 s delay demonstrates clear arterial enhancement of a nodule (arrows in (A)) and rapid washout (arrows in (B)), characteristic of metastasis.