A case of hepatic metastasis of neuroendocrine tumor presents a “spoke-wheel pattern” on contrast-enhanced ultrasonography

Abstract

A woman in her 50s presented to our clinic with a low-density area detected in hepatic segment 6 on unenhanced computed tomography. A low-echoic nodule with a clear border was observed on ultrasonography. Contrast-enhanced ultrasonography (CEUS) showed a meandering linear contrast enhancement pattern flowing into the nodule on vascular imaging in the arterial phase and a strong homogeneous enhancement pattern on perfusion imaging. The contrast enhancement pattern was relatively prolonged in the portal phase, and washout was not observed. In accumulation imaging, a blood vessel structure with a spoke-wheel pattern was identified. In the post-vascular phase, a clear defect with an irregular border measuring 17 mm was noted. After partial hepatectomy, a neuroendocrine tumor (NET) (G2) was diagnosed. The typical B-mode findings of NET-associated liver metastatic tumors are known to be uniform and slightly echogenic masses. CEUS findings consist of a uniformly strong enhancement pattern in the arterial phase, washout pattern in the portal phase, and a clear defect in the post-vascular phase. Differential diagnosis between metastatic NET and hepatocellular carcinoma (HCC) or focal nodular hyperplasia (FNH) is essential. Features that can be used to differentiate these are that HCC shows a relatively late washout and FNH often shows a spoke-wheel pattern on color Doppler and accumulation imaging in CEUS. However, some cases of FNH show a defect enhancement pattern in the post-vascular phase. We report a case of hepatic metastasis of NET that showed a spoke-wheel enhancement pattern on CEUS.