Pitfalls in contrast enhanced ultrasound: lack of washout in malignant liver lesions. A scoping review.

Contrast-enhanced ultrasound (CEUS) is a reliable examination procedure to differentiate benign and malignant liver lesions, which is superior to contrast enhanced computed tomography (CECT) and equally to contrast enhanced magnetic resonance imaging (CEMRI) in large comparative studies. In this review, the data on the enhancement of malignant liver lesions in the late phase in CEUS are analyzed in detail. Hypoenhancement in the late phase on CEUS with SonoVue^® is a typical feature of metastases and other malignant tumors. However, this is not guaranteed in every case. It is explicitly analyzed in the present studies which malignant lesions did not demonstrate washout in the late phase with SonoVue^®. Lack of washout is known for some hepatocellular carcinomas. However, there are also a few rare exceptions described for metastases of neuroendocrine tumors. The possible causes are analyzed. While metastases and cholangiocellular carcinoma demonstrate an early marked washout, this can start very late in neuroendocrine metastases. Some predominantly well differentiated hepatocellular carcinomas in the cirrhotic liver may also show no or only very delayed and faintly washout in the late phase. Isoenhancement at the beginning of the late phase does not rule out metastases or HCC (in the cirrhotic liver). This contrast behavior is known for some HCC in the cirrhotic liver, but it is atypical, poorly reported and understood, especially in liver metastases. The present review analyzes the data on isoenhancement in the late phase of malignant liver lesions. The novel aspect is the focus on liver metastases.