Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver. It is strongly associated with cirrhosis, from both alcohol and viral etiologies. HCC constitutes approximately 5% of all cancers partly due to the high endemic rates of hepatitis B infection 1.
HCC is the fifth most common cancer in the world and is the third most common cause of cancer-related death (after lung and stomach cancer). The incidence of HCC is rising, largely attributed to a rise in hepatitis C infection 11.
The demographics are strongly influenced by the regions in which chronic hepatitis B infection is common, which account for over 80% of cases worldwide. The highest prevalence is in Asia.
In Western countries the rate is lower and alcohol accounts for a greater proportion of cases.
Risk factors include 1:
- hepatitis B (HBV) infection: 10% 5-year cumulative risk 5
- hepatitis C (HCV) infection: 30% 5-year cumulative risk
- alcoholism: 8% 5-year cumulative risk
- biliary cirrhosis: 5% 5-year cumulative risk
- food toxins, e.g. aflatoxins
- congenital biliary atresia
- inborn errors of metabolism
HCC is typically diagnosed in late middle age or elderly adults (average 65 years) and is more common in males (75% cases) 21. The tumour can also occur in the paediatric population, however; it is the second most common paediatric primary liver tumour after hepatoblastoma.
Presentation is variable, and in affluent nations is often found in the setting of screening programs for patients with known risk factors. Otherwise presentation may include:
- constitutional symptoms
- portal hypertension from invasion of the portal vein
The origin of HCCs is believed to be related to repeated cycles of necrosis and regeneration, irrespective of cause. In addition the HBV and HCV genome contains genetic material that may predispose cells to accumulate mutations, or disrupts growth control, thus allowing for a second mechanism by which infection with these agents predisposes to HCC 1.
On gross pathology, HCCs typically appear as pale masses within the liver, and may be unifocal, multifocal or diffusely infiltrative at the time of presentation. Microscopically they range from well differentiated to undifferentiated.
Macroscopic growth of HCCs are usually categorized in three subtypes: nodular, massive and infiltrative. Each has different radiological features, which are detailed below 18. The infiltrative subtype is characterized by growth of multiple tiny nodule throughout the entire liver or an entire liver segment.
Metastasis occurs in the final stages of disease (IVA) and carry a poor prognosis 13-14. The most frequently involved sites are the lung, adrenal glands, lymph nodes, and bone.
Fibrolamellar hepatocellular carcinoma is distinct variant of HCC not associated with cirrhosis and has different demographics and risk factors.
- alpha-fetoprotein (AFP) levels are elevated in 50-75% of cases 11
Hepatocellular carcinomas can have a variety of appearances:
- massive (focal)
- large mass
- may have necrosis, fat and /or calcification
- nodular (multifocal)
- multiple masses of variable attenuation
- may also have central necrosis
infiltrative (diffuse) 19
- may be difficult to distinguish from associated cirrhosis – they also have been called cirrhotomimetic-type HCC or cirrhosis-like HCC
Hepatocellular carcinoma receives most of its blood supply from branches of the hepatic artery, accounting for its characteristic enhancement pattern: early arterial enhancement with early "washout." Hence, a small foci of HCC may be seen within a regenerative liver nodule, as a foci of arterial enhancement (nodule-in-nodule appearance) 15.
HCC uncommonly demonstrates a central scar similar to the FNH but differentiated by absence of delayed contrast enhancement of the scar (as seen in FNH). Also rim enhancement on delayed post contrast images represents a capsule which considered relatively specific for HCC (case 4).
Additionally these tumours have a propensity to invade vascular structures, most commonly the portal vein, but also the hepatic veins, IVC and right atrium. One should remember that a large number of patients will have concomitant cirrhosis, and thus also be at risk for bland portal vein thrombosis from synthetic dysfunction of clotting factors.
Several patterns can be seen, depending on the subtype of HCC. Enhancement pattern is the key to correct assessment of HCCs.
Usually the mass enhances vividly during late arterial (~35 seconds) and then washes out rapidly, becoming indistinct or hypoattenuating in the portal venous phase, compared to the rest of the liver.
Additionally, they may be associated with a wedge shaped perfusion abnormality due to arterioportal shunts (APS), and this in turn can result in focal fatty change in the normal liver or focal fatty sparing in the diffusely fatty liver 7. A halo of focal fatty sparing may also be seen around an HCC in an otherwise fatty liver 6.
Portal vein tumour thrombus can be distinguished from bland thrombus by demonstrating enhancement.
Variable appearance depending on individual lesion, size, and echogenicity of background liver.
Typically a small focal HCC appears hypoechoic compared with normal liver. Larger lesions are heterogeneous due to fibrosis, fatty change, necrosis and calcification 8. Again, a peripheral halo of hypoechogenicity may be seen with focal fatty sparing.
Diffuse HCC may be difficult to identify or distinguish from background cirrhosis. A positive serum AFP level and/or biopsy may be necessary for diagnosis.
- contrast-enhanced ultrasound 17
- arterial phase
- arterial enhancement from neovascularity
- portal venous phase
- decreased echogenicity relative to background liver ("wash out")
- tumour thrombus may be visible
- arterial phase
Variants have been described with arterial phase hypovascularity with no enhancement or arterial enhancement with no "washout".
In general, MRI signal is:
- iso- or hyperintense cf. surrounding liver
- hyperintensity may be due to
- intratumoral fat 5
- decreased intensity in surrounding liver
T1 C+ (Gd)
- enhancement is usually arterial ("hypervascularity")
- rapid "washout," becoming hypointense to the remainder of the liver (96% specific) 5
- this is because the supply to HCCs is predominantly from the hepatic artery rather than portal vein
- rim enhancement may persist (referred to as a capsule)
- an imaging classification system (LI-RADS) has been developed to risk stratify lesions
T1 C+ (Eovist/Primovist)
- similar to assessment with extracellular Gd, but evaluation of the hepatobiliary phase requires care (see: Eovist and LI-RADS)
- T2: variable, typically moderately hyperintense
- C+ post SPIO (iron oxide): increases sensitivity in diagnosing small HCCs
- hypervascular tumour
- threads and streaks pattern: sign of tumour thrombus in portal vein
Staging and classification
The typical TNM staging system seen in most other epithelial cancers is not as prognostically useful for stratification of patients with hepatic cancers.
There are several substitute staging systems used in guiding therapy for hepatocellular carcinoma 16. An imaging classification system (LI-RADS) has been developed to risk stratify lesions in an at-risk liver.
Treatment and prognosis
If the lesion is small then resection is possible (partial hepatectomy) and may result in cure. The remarkable ability of the liver to regenerate means that up to 2/3rds of the liver can be resected 10.
Liver transplantation is also a curative option. To be suitable for a liver transplantation it is generally agreed that certain criteria should be met (see Milan criteria).
If neither of these options is possible, then a variety of options exist including chemotherapy, transarterial chemoembolisation (TACE), thermal ablation (RFA, cryoablation, or microwave ablation) and selective internal radiation therapy (SIRT) 12.
If a tumour is resectable, then 5 year survival is ~45% (range 37-56%) 3.
General imaging differential considerations include:
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