Radiation Therapy for Liver Tumors by Jeffrey Meyer & Tracey Schefter

Author:Jeffrey Meyer & Tracey Schefter
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

As noted above, patients with a positive surveillance test should be evaluated with triple-phase CT or contrast-enhanced MRI. Established protocols for CT and MRI define the amount and method of contrast administration, timing of the studies after contrast administration, and thickness of slices required for adequate resolution. Several studies have compared performance characteristics of CT and MRI as diagnostic modalities for HCC [100–103]. The sensitivity of MRI is 61–95% compared to 51–86% for triple-phase CT [104]. The role of other imaging modalities, including contrast-enhanced ultrasound, remains debated [105, 106]. Positron emission tomography has poor performance for HCC diagnosis and is not included in the diagnostic algorithm [107].

HCC lesions enhance more than the surrounding liver in the arterial phase and less than the hepatic parenchyma in the venous and delayed phases. Arterial enhancement is an essential characteristic of HCC but is non-specific, as it can be seen in other hypervascular hepatic lesions, such as hemangioma and focal nodular hyperplasia as well as some metastases [108, 109]. Delayed washout is the strongest predictor of HCC among those with an arterial-enhancing lesion (OR 61, 95% CI 3.8–73) [93]. The presence of arterial enhancement and delayed washout had a sensitivity of 89% and specificity of 96% for HCC. The phenomenon of “arterial enhancement and delayed washout” is related to the differential blood supply of the tumor compared to the surrounding liver [102, 110]. The liver obtains ~75% of its blood supply from the portal vein and the remainder from the hepatic artery. As a dysplastic nodule transitions to HCC, there is a gradual reduction in the portal blood supply to the nodule and an increase in arterial blood flow from hepatic artery branches through neoangiogenesis [111, 112]. In the arterial phase, HCC receive contrast-containing arterial blood, while arterial blood to the surrounding liver is diluted by venous blood without contrast. In the portal venous and delayed phases, HCC tumors do not receive any contrast given lack of a portal venous blood supply, while the surrounding liver receives portal blood with contrast.

Lesions between 1 and 2 cm demonstrate typical imaging characteristics less often than larger lesions and can pose the most difficulty for diagnosis. Many of these lesions are not malignant; however, some small HCC lesions can have aggressive behavior leading to vascular invasion and poor survival if not diagnosed early [93–96]. Although requiring one characteristic contrast-enhanced study to make a diagnosis of HCC in 1–2 cm lesions has a lower positive predictive value than requiring two studies, the positive predictive value still exceeds 90% [92, 97, 98]. Serste and colleagues validated this approach in a study among 74 patients with 1–2 cm nodules, of whom 47 had HCC [99]. The sensitivity and specificity of characteristic findings on one imaging study, for the detection of HCC or high-grade dysplatic nodules, was 96 and 100%, respectively, compared to 57 and 100% if characteristics findings were required on both studies. Liver biopsy provided an accurate diagnosis in the 21 (28%) patients with discordant imaging findings on CT and MRI.

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