HEPATOCELLULAR CARCINOMA IMAGING

Hepatocellular carcinoma (HCC)
This primary carcinoma of the liver is more common in Africa and the Far East than in the UK. Most HCCs arise in diseased livers, hence the strong association with alcoholic cirrhosis and hepatitis, and one of the main reasons for ultrasound referral in these patients is to try to exclude focal liver lesions which could represent carcinoma. HCC is also associated with metabolic disorders and drug-related liver disease. Clinically, small tumours are asymptomatic but cause a raised serum alpha-fetoprotein (AFP). The relationship between cirrhosis and HCC prompts screening of such patients with AFP and ultrasound.

The ultrasound appearances of HCC vary from hypoechogenic to hyperechogenic or mixed echogenicity lesions. It is often particularly difficult to locate small HCCs in a cirrhotic liver which is already coarse-textured and nodular. CT and MRI may be useful in these cases. These lesions may be solitary or multifocal. Colour and spectral Doppler can demonstrate vigorous flow, helping to distinguish HCCs from metastases or haemangiomas, which demonstrate little or no flow. All carcinomas demonstrate neovascularization: the formation of numerous new blood vessels to supply the growing lesion.

The vascular characteristics of such new vessels are different from those of the normal, established vessels. The lesion usually demonstrates a knot of short, tortuous vessels with an irregular course. Because these new vessels have a paucity of smooth muscle in the intima and media, they exhibit a low resistance to blood flow, having relatively high end diastolic flow (EDF). They are able to multiply relatively quickly, causing arteriovenous shunting within the mass which may result in high velocities.

Increasingly, contrast ultrasound is used to detect and characterize HCCs in patients with a background of liver disease. HCCs tend to demonstrate an early enhancement of tortuous vessels, followed by a ‘blush’ of arterial enhancement compared to normal liver.