Once a lesion is detected by US, further characterization can be performed by multiphasic CT or MRI. Both modalities image the entire liver rapidly several times. The liver is scanned once when the intravenously administered contrast is perfusing the liver via the hepatic artery (hepatic arterial phase) and subsequently imaged again when the portion of the contrast perfusing the bowel in the arterial phase has circulated to the liver via the portal vein (portal venous phase). Later acquisitions are also performed in the equilibrium phase when the contrast has re-circulated the body a few times.

With the advent of modern radiation equipment and computer planning software technology, 3-dimensional conformal radiotherapy (3DCRT) has become a reality. This allows easy conformation of the target volume using CT computer planning and electronically controlled mechanical blocks called multileaf-collimators (MLCs).

The imaging features that suggest hepatoma include hypervascularity in the hepatic arterial phase fading in the portal venous phase; pseudocapsule and internal septae enhancing in the portal venous phase; and a multinodular or mosaic appearance.

Triphasic (or multiphasic) CT has traditionally been the modality of choice. However, MRI is fast gaining popularity as it is not only able to detect more lesions but also definitively characterizes benign lesions of the liver such as hemangiomas, focal fatty change, focal fatty sparing and cysts. Angiography and CT Lipiodol have been superceded by triphasic CT and MRI. CT Lipiodol has recently been shown to have a high false positive rate and is not used as a means of diagnosis. Transarterial chemoembolization with Lipiodol remains an important treatment modality.

The imaging features are not pathognomonic of hepatoma. Differential considerations include FNH, adenoma and hypervascular metastases such as neuroendocrine tumor. If a lesion is single and operable, surgery often serves as the diagnostic and curative procedure. Percutaneous biopsy is contraindicated in these patients as there is a 3% risk of seeding could potentially deny cure. In the setting of a cirrhotic liver and elevated AFP, an imaging diagnosis of hepatoma is often presumed if the lesion is 2cm or larger and if it demonstrates hepatic arterial enhancement in 2 modalities. Histology by surgery or percutaneous biopsy can be considered in other situations.

Figure 1
The hepatoma next to the gallbladder bed is hardly seen on the hepatic arterial phase of the CT examination.

Figure 2
The hepatic arterial phase of the MRI examination clearly depicts the hepatoma which was proven by surgical resection.