Hepatic Sarcomas 6141

Angiosarcoma

Hepatic angiosarcoma (HAS) is a very rare neoplasm that occurs more frequently in males than in females and most typically in the seventh decade of life. In the general population, HAS accounts for only 1.8% of all primary hepatic neoplasms and is 30 times less common than HCC [43]. It is associated with previous exposure to toxins such as Thorotrast, vinyl chloride, arsenicals, steroids, radium and possibly copper [9, 99] and also with chronic idiopathic hemochromatosis [98] and von Recklinghausen disease [2]. Angiosarcoma represents approximately 25% of liver tumors in patients with proven thorium exposure. Although

40% of patients have hepatic fibrosis or cirrhosis at autopsy, the nature of the association between chronic liver disease and HAS is unknown. Further study is also required to delineate the cause of HAS in the remaining 60% of cases without a definitive etiologic association.

Histologically, HAS is composed of malignant endothelial cells lining vascular channels of variable size, from cavernous to capillary, which attempt to form sinusoids. Thorotrast particles can be found within the malignant endothelial cells in cases of Thorotrast-induced HAS [46].

Macroscopically, the majority of angiosarco-mas present as multiple nodules, often with areas of internal hemorrhage. When present as a single, large mass, there is no capsule and frequently large cystic areas filled with blood debris [11].

The clinical presentation is non-specific, with abdominal pain, weakness and weight loss as fre quent complaints, and with hepatomegaly, ascites and jaundice as common findings. Liver function parameters are usually altered but no parameter or set of parameters is specific for the tumor. The occurrence of thrombocytopenia and disseminated intravascular coagulation is characteristic of HAS and may be related to the local derangement of clotting factors and blood cells by the tumor. Massive intra-abdominal hemorrhage is a complication which occurs in 25% of cases and is probably related to the high incidence of coagulation deficits and to the vascular nature of the neoplasm [44,63].

On US scans, angiosarcomas are seen as either single or multiple hyperechoic masses. The echo architecture is usually heterogeneous due to the presence of hemorrhage of various ages [87].

CT images reveal the reticular pattern of deposition of Thorotrast extremely well in both liver and spleen. Circumferential displacement of Thorotrast in the periphery of a nodule is a characteristic finding of HAS. When there is no evidence of Thorotrast deposition, angiosarcomas present on unenhanced CT as single or multiple hypodense masses containing hyperdense areas of fresh hemorrhage. Many angiosarcomas are hy-poattenuating compared to the liver on both arterial and portal-venous phase images after the administration of contrast material. However, a few lesions are hyperattenuating on arterial phase images, becoming isoattenuating on portal-venous phase images [81]. Centripetal contrast enhancement simulating the pattern of enhancement in hemangioma may occur. The earlier CT reports of angiosarcoma mimicking hemangioma can likely be attributed to imaging in a single temporal phase, often during the delayed phase of contrast enhancement, and to the evaluation of lesion enhancement relative to liver parenchyma rather than the aorta or hepatic artery. Temporal assessment by means of multiphasic helical CT of the various patterns of angiosarcoma enhancement in comparison with the pattern of normal vascular enhancement allows confident exclusion of the diagnosis of hemangioma [81].

On T1-weighted MR images, angiosarcomas are usually seen as hypointense with areas of hy-perintensity corresponding to hemorrhage. Conversely, on T2-weighted images, the signal intensity is predominantly high, with areas of low signal [105]. Experience of contrast-enhanced MR imaging of HAS is very limited. On dynamic contrast-enhanced MR images, the enhancement pattern of HAS is usually different to that of cavernous he-mangioma and similar to that observed with spiral CT [81]. Generally, diffuse or central enhancement is seen, although in some cases peripheral enhancement and centripetal filling-in of the lesion is observed. In these cases, irregular borders may contribute to the diagnosis. On equilibrium phase images, the lesion appears as a homogeneous, well-defined hyperintense mass (Fig. 37).

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