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Computed Tomography (Fig. 1,2,3)
Gross Pathology
HistologyThree contrast-enhanced images from the computed tomography (CT) study are shown. The first image represents the early arterial phase. A heterogeneously enhancing mass, approximately 4-5 cm in size, is visible in the liver. There is no evidence of calcifications. The late-arterial phase image (figure 2) demonstrates additional enhancement of the mass. On the portal venous phase image (figure 3), the enhancement has decreased. The mass is iso-attenuating with the rest of the liver.
A biopsy of the mass was followed by a magnetic resonance (MR) study, not shown. A capsule was apparent in the MR image.
The gross image demonstrates a firm, white mass (6 cm). The first microscopic image shows the boundary between the mass and the liver parenchyma. The parenchyma is involved by hepatitis and cirrhosis. The second image, at higher magnification, reveals that the mass is composed of hepatocyte-like cells with increased nuclear to cytoplasmic ratios. In addition, the architecture is very disorganized. Some hepatocytes are arranged in a trabecular pattern but these trabeculae are often more than two cells thick. There are also sheet-like and aciniform (pseudoglandular) areas. These features are characteristic of Hepatocellular Carcinoma.
Radiology Discussion
Hepatocellular carcinoma (HCC) is the most common abdominal malignancy, representing 80-90% of primary liver malignancies around the world. Its incidence peaks between the ages 50-70 years, and it is more common in men. Risk factors include cirrhosis, chronic hepatitis, carcinogens, and errors of metabolism. HCCs can be solitary, multicentric, diffuse, and infiltrating. The lesions may invade adjacent vascular structures and metastasize to the lung(s), adrenal gland(s), lymph nodes, or bone.
The vascularity of the capsule leads to enhancement on both CT and late-phase MR images. On CT, most lesions are visible on arterial phase imaging (80%), with washout of contrast in the portal venous phase. The appearance of the lesion on CT varies primarily with size; small lesions are more homogenous, while large lesions may exhibit mosaic pattern due to necrosis and fatty change. The capsule may be visible on CT. On MR images, the lesion will show vascular enhancement similar to CT. Signal intensity with vary on T1- and T2-weighted sequences. High signal on T1 may be due to fat or glycoproteins. In the high-risk cirrhotic population, the overall sensitivity of CT and MR for diagnosis of HCC is similar: 59-68% for CT vs. 50% for MR.
Cirrhosis is both a risk factor and a confounding factor for HCC. The nodularity of the cirrhotic liver may obscure HCC on diagnostic images. In a study of patients with cirrhosis (Baron 2001), CT and MR detected only 37-50% of total lesions and returned false positive results at a rate of 8%. In addition, the morphological changes and portal hypertension that characterize cirrhosis may take years to develop. It is important to consider the possibility of HCC whether or not a patient has been previously diagnosed with cirrhosis. In addition to HCC, the differential diagnosis for enhancing lesions in the liver of a cirrhotic patient should include:
Dahnert W. Radiology Review Manual. Baltimore, MD: Williams & Wilkins; 1999.
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