Original contributions
Small hepatocellular carcinomas in cirrhosis: differences in contrast enhancement effects between helical CT and MR imaging during multiphasic dynamic imaging

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Abstract

Purpose

The purpose of this study was to evaluate differences in the degrees of contrast enhancement effects of small hepatocellular carcinomas (HCCs) in patients with cirrhosis between helical computed tomography (CT) and magnetic resonance (MR) imaging during multiphasic contrast-enhanced dynamic imaging and to determine the diagnostic value of MR imaging especially in assessing hypovascular HCCs detected as hypoattenuating nodules on late-phase CT.

Subjects and Methods

This study included 64 small HCCs (<3 cm in diameter) in 40 patients with chronic hepatitis or cirrhosis who underwent multiphasic (arterial, portal and late phases) contrast-enhanced dynamic helical CT and MR imaging. The contrast enhancement patterns of each lesion in the arterial and late phases were evaluated by two radiologists experienced in liver MR imaging and categorized as one of five grades (1=hypoattenuated/hypointense; 2=slightly hypoattenuated/hypointense; 3=isoattenuated/isointense; 4=slightly hyperattenuated/hyperintense; 5=hyperattenuated/hyperintense), compared with the surrounding liver parenchyma.

Result

Forty-three (67%) of 64 lesions showed Grade 4 (n=24) or Grade 5 (n=19) enhancement on arterial-phase CT, while 51 (80%) of 64 lesions showed Grade 4 (n=20) or Grade 5 (n=31) enhancement on arterial-phase MR imaging, indicating hypervascular HCCs. The grading score of hypervascular HCCs on arterial-phase MR imaging (mean: 4.61) was significantly (P<.01) higher than that for hypervascular HCCs on arterial-phase CT (mean: 4.20), showing better detection of the hypervascularity (arterial enhancement) of the lesion on arterial-phase MR imaging. Regarding hypovascular HCCs, all (100%) of 21 hypovascular HCCs on CT showed Grade 1 (n=10) or Grade 2 (n=11) enhancement on late-phase CT, seen as hypoattenuation. In contrast, 8 (62%) of 13 hypovascular HCCs on MR imaging showed Grade 1 (n=1) or Grade 2 (n=7) enhancement on late-phase MR imaging, seen as hypointensity. Grading scores of hypovascular HCCs on late-phase images were significantly (P<.001) lower on CT than on MR imaging (mean score: 1.52 vs. 2.31), indicating better washout effects for hypovascular HCCs on late-phase CT.

Conclusion

The washout effects for small HCCs on late-phase MR imaging were inferior to those for small HCCs on late-phase CT. Especially, hypovascular HCCs demonstrated as hypoattenuating nodules on late-phase CT were often not seen on late-phase MR imaging, requiring careful evaluation of other sequences, including unenhanced T1-weighted and T2-weighted MR images.

Introduction

Multiphasic contrast-enhanced helical computed tomography (CT) and magnetic resonance (MR) imaging have been widely used as accurate screening modalities for patients with cirrhosis and suspected hepatocellular carcinomas (HCCs) [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. Arterial-phase contrast-enhanced CT and MR imaging are especially important for the detection of hypervascular HCCs [5], [10], [16], [17] because these HCCs show discrete early enhancement on arterial-phase imaging. These hypervascular HCCs usually become hypoattenuating relative to the surrounding liver parenchyma due to “washout” effects on late-phase CT. However, we have sometimes encountered small HCCs without “washout” effects on late-phase MR imaging compared with late-phase CT, resulting in unsuccessful detection of HCCs on this phase of MR imaging. This fact may lead to hypovascular HCCs without early enhancement being overlooked on multiphasic contrast-enhanced dynamic MR imaging. The purpose of this study was to evaluate differences in the degrees of contrast enhancement effects of small HCCs in patients with cirrhosis between helical CT and MR imaging during multiphasic contrast-enhanced dynamic imaging and to determine the diagnostic value of MR imaging especially in assessing hypovascular HCCs detected as hypoattenuating nodules on late-phase CT.

Section snippets

Patients

This study included 64 small HCCs (<3 cm in diameter) in 38 consecutive patients with chronic hepatitis or cirrhosis who underwent multiphasic (arterial, portal/venous and late phases) contrast-enhanced dynamic helical CT and MR imaging at 3-month intervals from June 2002 to May 2004. The patients included 23 men and 15 women who ranged in age from 41 to 83 years (mean age, 72 years). All patients had chronic hepatitis or liver cirrhosis with suspected HCC. The causes of cirrhosis were as

Results

Forty-three (67%) of 64 lesions showed Grade 4 (n=24) or Grade 5 (n=19) enhancement on arterial-phase CT, indicating hypervascular HCCs on CT (Fig. 1). In contrast, 51 (80%) of 64 lesions showed Grade 4 (n=20) or Grade 5 (n=31) enhancement on arterial-phase MR imaging, indicating hypervascular HCCs on MR imaging. All of the 43 hypervascular HCCs on arterial-phase CT were included in the 51 hypervascular HCCs on MR imaging. The grading score of hypervascular HCCs on arterial-phase MR imaging

Discussion

Because most HCCs are hypervascular, arterial-phase imaging is mandatory in multiphasic dynamic CT and MR imaging [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. Conversely, some well-differentiated or early HCCs tend to be hypovascular and are best seen during the late phase of CT or MR imaging [7], [10], [18], [19], [20]. Although the diagnostic ability of multiphasic contrast-enhanced dynamic CT and MR imaging for the detection of HCCs has been well evaluated

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