CT and MRI features of HCC
What is HCC, and what are its CT and MR imaging features?
HCC is the most common primary malignant tumor of the liver, is more commonly seen in men than in women, usually in patients who are >50 years of age in the Western hemisphere, and typically occurs in the setting of chronic liver damage, most often related to chronic hepatitis or cirrhosis. It is solitary in 50%, multifocal in 40%, and diffuse in 10% of cases and may sometimes be associated with direct extrahepatic extension, regional lymphadenopathy, or distant metastatic disease.
Regenerative changes in the liver in response to liver damage lead to formation of regenerative nodules. With time, a regenerative nodule can progress to a dysplastic nodule, and then potentially to HCC. HCC predominantly receives hepatic arterial blood supply, whereas a regenerative nodule predominantly receives portal venous blood supply, accounting for differences in their enhancement patterns observed on cross-sectional imaging.
The classic enhancement pattern of HCC on both CT and MRI often includes heterogeneous arterial phase enhancement, venous phase washout (i.e., low attenuation or low signal intensity relative to liver parenchyma), presence of an enhancing pseudocapsule (representing a peripheral rim of compressed hepatic parenchyma) on delayed phase images, and hypointense signal intensity relative to liver parenchyma on hepatobiliary phase images given the lack of retention of hepatobiliary contrast material. On MRI, high T2-weighted signal intensity relative to liver parenchyma (but similar to spleen) and restricted diffusion are additional highly suggestive findings for presence of HCC, especially when encountered within a cirrhotic liver.
Note that although similar imaging features may be seen with metastases to the liver, metastatic disease to a cirrhotic liver is extremely rare. Therefore, when lesions with suspicious imaging features are seen in a cirrhotic liver, they are assumed to be caused by HCC until proven otherwise, even in patients with known extrahepatic cancer.
Small arterial phase enhancing foci in a cirrhotic liver may sometimes be secondary to arterioportal venous shunts and/or altered hepatic blood flow dynamics. However, these changes are not visualized during other phases of contrast enhancement or on precontrast images. On follow-up cross-sectional imaging, these will generally resolve, decrease in size, or remain stable, whereas HCC tends to grow over time.
Tumor thrombus within the portal or hepatic veins is an additional imaging manifestation of HCC. Compared to bland thrombus, tumor thrombus can be suggested by the presence of high T2-weighted signal intensity and restricted diffusion, enhancement, venous luminal expansion, or presence of contiguous adjacent HCC.
