Abdominal Imaging

ª Springer Science+Business Media, Inc. 2006 Published online: 26 June 2006

Abdom Imaging (2006) 31:529–536 DOI: 10.1007/s00261-005-0066-5

Focal liver lesions: sinusoidal phase of CEUS M. DÕOnofrio, E. Martone, N. Faccioli, G. Zamboni, R. Malago`, R. Pozzi Mucelli Department of Radiology, Policlinico G. B. Rossi, University of Verona, Piazzale L. A. Scuro 10, 37134, Verona, Italy

Abstract Ultrasound examination is the first imaging modality for hepatic study in neoplastic and chronic liver diseases. Focal liver lesions frequently cause diagnostic problems in terms of characterization, especially when small and hypoechoic to the rest of the parenchyma. Contrastenhanced ultrasonography (CEUS) has shown its value in the characterization of focal liver lesions. This study assessed the value of the sinusoidal phase of CEUS with a second-generation contrast agent in the characterization of focal liver lesions to distinguish benign from malignant. Two hundred hepatic lesions with suspicious features at baseline ultrasound were prospectively studied with CEUS. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of the sinusoidal phase in the characterization of benign versus malignant liver lesions were evaluated. Hypoechogenicity of the focal liver lesion, during the sinusoidal phase of CEUS, allowed the diagnosis of malignancy with a sensitivity of 85%, specificity of 88%, positive predictive value of 92%, negative predictive value of 77%, and diagnostic accuracy of 86%. The diagnostic confidence in the diagnosis of malignancy significantly increased, with receiver operating characteristic curve areas from 0.536 for baseline ultrasound to 0.902 for the sinusoidal phase of CEUS. Key words: Contrast-enhanced ultrasound—Computed tomography—Magnetic resonance imaging—Liver neoplasms—Hepatocellular carcinoma

Ultrasound (US) examination is the first imaging modality for hepatic study in neoplastic and chronic liver diseases. Solid focal liver lesions frequently cause diagnostic problems in terms of characterization, especially when lesions are small and hypoechoic in relation to the rest of the parenchyma [1–3]. Characterization of focal liver

Correspondence to: M. DÕOnofrio; email: [email protected]

lesions is based on the US and color/power Doppler features and, more recently, on contrast-enhanced dynamic study results [3]. Contrast-enhanced US (CEUS) has shown its value in the characterization of focal liver lesions with enhancement patterns similar to those known for computed tomography (CT) and magnetic resonance imaging (MRI) [3–6]. However, evaluation of the appearance of focal liver lesions with CEUS is limited to one lesion at a time. Continuous US scan at low sound pressure during the sinusoidal phase of CEUS is used for the detection of liver metastases, with the advantage of an entire liver parenchyma study [2, 4, 5]. Most US microbubble contrast agents are exclusively blood pool agents because they do not leave the intravascular space; hence, in the sinusoidal phase, a pooling in the liver and spleen sinusoids is possible [5]. This study assessed the value of the sinusoidal phase of CEUS with a second-generation contrast medium in the characterization of focal liver lesions to distinguish benign from malignant lesions.

Materials and methods Between 2002 and 2004, 200 consecutive liver lesions were prospectively examined with CEUS. Inclusion criteria were hypoechoic pattern of the focal liver lesion or focal liver lesion in patients at high risk for liver malignancy. All patients signed an informed consent before the examination. PatientsÕ ages ranged from 18 to 86 years; 69 patients were women and 131 were men. Ninety-two patients presented with cirrhosis and 54 were oncologic patients. One hundred nineteen patients had single focal liver lesions and 81 had multiple lesions at baseline US. In patients with multiple lesions, only the largest lesion for each patient was examined with CEUS. The final diagnosis was obtained with contrast-enhanced spiral CT, MRI, and biopsy, which were considered gold standard modalities (Table 1). All lesions thought to be benign at imaging were followed with US and/or CT plus MRI. Available follow-up was 6 to 12 months.

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Table 1. Final diagnosis of 200 focal liver lesions Diagnosis

n

CT

MRI

Biopsy/surgery

Benignancy Cavernous hemangioma Capillary hemangioma Focal nodular hyperplasia Fat-spared region Adenoma Intrahepatic necrotic area Malignancy Hepatocellular carcinoma Metastatic carcinoma Metastatic endocrine tumor Cholangiocellular carcinoma Lymphoma Total

73 38 3 19 7 4 2 127 87 26 10 2 2 200

17 7 — 6 4 — — 65 50 11 4 — — 82

47 30 3 10 3 — 1 25 16 5 3 1 — 72

6/3 1/— —/— 2/1 —/— 3/1 —/1 22/15 10/11 8/2 2/1 —/1 2/— 28/18

CT, computed tomography; MRI, magnetic resonance imaging

All CEUS examinations were performed on a Sequoia 512 with version 6.0 software (Siemens, Erlangen, Germany) with 2.4 mL of a second-generation contrast agent that consisted of sulphur hexafluoride in the form of microbubbles (SonoVue , Bracco, Milan, Italy) that was injected intravenously by using a 20-gauge cannula as a rapid bolus followed by a 5-mL saline flush. We performed continuous insonation with low US pressure (2 to 4 MHz; mechanical index < 0.2). The sinusoidal phase of CEUS started 2 min after contrast injection [6]. All CEUS examinations were performed by the same radiologist and recorded on videotape/VHS or magneto optical disk systems to immediately review the dynamic study. Lesional enhancement was evaluated with a separate and independent review of the recorded examination by two radiologists; evaluation was performed blinded to the clinical data and any disagreement was resolved by means of consensus after discussion. Considering the baseline US and only the sinusoidal phase of CEUS, the studied focal liver lesion was judged as hypointense, isointense, or hyperechoic in relation to the rest of the parenchyma. Spiral CT study of the liver was performed on a single-slice scanner (Somatom Plus 4, Siemens) with iodinated contrast medium and triphasic technique. After unenhanced acquisitions, 130 mL of non-ionic contrast medium (Ultravist 370, Schering, Berlin, Germany) was administered at a flow rate of 3 mL/s with an EnVision CT (Medrad, USA) power injector. Spiral acquisition was obtained with a fixed start delay. Arterial phase was obtained 25 s after contrast injection; venous phase was obtained with an 80-s delay. Scan parameters were the same for all phases: 5-mm collimation, 7.5-mm/rotation table increment, and 5-mm reconstruction interval. All MRI examinations were performed on a 1.5-T Magnetom Symphony scanner (Siemens) with high-performance gradients and a phased array body coil. The unenhanced liver study protocol included a spoiled gradient echo T1-weighted sequence in and out of phase (repetition time 75 ms, echo time 2.4 ms, inversion time

4.8 ms, flip angle 70°), a turbo spin-echo T2-weight sequence (repetition time 1800 ms, echo time 84 ms, echo train length 15), turbo inversion recovery T2-weighted (repetition time 5000 ms, echo time 103 ms, inversion time 145 ms, echo train length 33) axial breath-hold sequences with 8-mm slice thickness, and a half Fourier acquisition T2-weighted (repetition time 1000 ms, echo time 82 ms, echo train length 144) ‘‘free-breathing’’ fatsaturated sequence. Dynamic study was performed after administration of dimeglumine-gadobenate (Multihance, Bracco) with a three-dimensional fat-saturated gradientecho T1-weighted sequence called volume interpolated breath-hold examination (repetition time 4.5 ms, echo time 1.7 ms, flip angle 10°). Final imaging diagnosis for each lesion was made on the basis of enhancement patterns previously described at CT and MRI [7–10]. All lesion biopsies were performed under US guidance with a 20-, 19-, or 18-gauge Menghini type needle with automatic aspiration (Biomol, Hospital Service, Rome, Italy) or a Menghini type needle with manual aspiration (Surecut, Hospital Service). The sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of the sinusoidal phase of CEUS in the characterization of the examined liver lesions, i.e., benign versus malignant, were evaluated. During the sinusoidal phase of CEUS, the hypoechogenicity of the examined focal liver lesion (‘‘clear hypoechoic defect’’) [11] was considered diagnostic for malignancy. Each focal liver lesion was evaluated at baseline US and at CEUS with a three-level diagnostic score (1, hyperechoic, i.e., benign; 2, isoechoic, i.e., indeterminate; 3, hypoechoic, i.e., malignant). The indeterminate and benign lesion groups were considered together for data analysis to evaluate the value of the hypoechogenicity of the examined focal liver lesion as diagnostic for malignancy. Lesions characterized as malignant at CEUS and with the gold standard modalities were defined as true positives (TP). Lesions considered malignant with the gold standard modalities but

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Fig. 1. Atypical focal nodular hyperplasia. A CEUS in the arterial phase shows a hypervascular focal liver lesion (arrow) in the right hepatic lobe. B CEUS in the sinusoidal phase visualizes the focal liver lesion as hypoechoic (arrow) to

adjacent hepatic parenchyma. C Resected specimen. D At immunohistochemical analysis (CD34 antigen), the lesion shows a strong positivity for the marker.

characterized as benign at CEUS were considered false negatives (FN). Lesions characterized as benign at CEUS and gold standard modalities were defined true negatives (TN). Lesions characterized as benign at gold standard modalities and as malignant at CEUS were rated as false positives (FP). Sensitivity was calculated as the ratio of TP to the total number of malignant lesions. Specificity was calculated as the ratio of TN to the total number of benign lesions. Positive predictive value was calculated as the ratio between the number of TP and the sum of TP plus FP. Negative predictive value was calculated as the ratio between TN and the sum of TN plus FN. Diagnostic accuracy was calculated as the result of TP+TN/ TP+TN+FP+FN. Diagnostic confidence of baseline US and sinusoidal phase of CEUS in the characterization

of focal liver lesions, i.e., benign versus malignant, were represented by means of receiver operating characteristic curves; any diagnostic advantage of sinusoidal phase CEUS versus baseline US was calculated by comparing the areas under the receiver operating characteristic curves, which were obtained by using Analise-it 1.63 (Analise-it Software, Leeds, UK).

Results Of 200 solid focal liver lesions, 170 (85%) were hypoechoic on baseline US and ranged from 1 to 15 cm. On the basis of biopsy and/or CT and/or MRI, 73 lesions were benign (36.5%) with a diameter ranging from 1 to 10 cm (38 cavernous hemangiomas, 3 capillary

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Table 2. Contrast-enhanced ultrasound in the sinusoidal phase of 200 focal liver lesions Sinusoidal phase Final diagnosis

n

Hypoechoic

Isoechoic

Hyperechoic

Benignancy Cavernous hemangioma Capillary hemangioma Focal nodular hyperplasia Fat-spared region Adenoma Intrahepatic necrotic area Malignancy Hepatocellular carcinoma Metastatic adenocarcinoma Metastatic endocrine tumor Cholangiocellular carcinoma Lymphoma Total

73 38 3 19 7 4 2 127 87 26 10 2 2 200

9 2 0 4 0 1 2 108 68 26 10 2 2 117

18 1 1 6 7 3 0 16 16 0 0 0 0 34

46 35 2 9 0 0 0 3 3 0 0 0 0 49

hemangiomas, 19 focal nodular hyperplasias, 7 focal areas spared from steatosis, 4 adenomas, and 2 intrahepatic necroses) and 127 were malignant (63.5%) with a diameter of 1 to 15 cm (87 hepatocellular carcinomas, 26 adenocarcinoma metastases, 10 endocrine tumor metastases, 2 cholangiocellular carcinomas, and 2 lymphomas).

Benign lesions Nine benign lesions were hypoechoic at CEUS in the sinusoidal phase (Fig. 1): two of 38 (5%) cavernous hemangiomas, four of 19 (21%) focal nodular hyperplasias, one of four (25%) adenomas, and two of two (100%) intrahepatic necroses (Table 2). Sixty-four benign lesions were isoechoic or hyperechoic at CEUS in the sinusoidal phase (Fig. 2): 36 of 38 (95%) cavernous hemangiomas, three of three (100%) capillary hemangiomas, 15 of 19 (79%) focal nodular hyperplasias, seven of seven (100%) focal areas spared from steatosis, and three of four (75%) adenomas (Table 2). In 12 of 15 (80%) focal nodular hyperplasias, the central scar was visible as a hypoechoic defect.

Malignant lesions One hundred eight malignant lesions were hypoechoic at CEUS in the sinusoidal phase (Fig. 3): 68 of 87 (78%) hepatocellular carcinomas, two of two (100%) cholangiocellular carcinomas, 26 of 26 (100%) adenocarcinoma metastases, 10 of 10 (100%) endocrine tumor metastases, and two of two (100%) lymphomas (Table 2). Sixty-eight of the 87 hepatocellular carcinomas (78%) were hypoechoic in the sinusoidal phase (Fig. 4). Sixteen (18%) were isoechoic (Fig. 5) and three (4.6%) were hyperechoic in the sinusoidal phase. The 64 benign focal liver lesions that were isoechoic or hyperechoic at CEUS in the sinusoidal phase were TN. The 108 malignant focal lesions that were hypo-

Fig. 2. Focal nodular hyperplasia. A CEUS in the arterial phase displays a small hypervascular focal liver lesion (arrow) in the right hepatic lobe. B CEUS in the sinusoidal phase shows the small focal liver lesion as slightly hyperechoic (arrow) to adjacent hepatic parenchyma.

echoic in the sinusoidal phase were TP. The nine benign lesions that were hypoechoic at CEUS in the sinusoidal phase were FP. The 16 and three hepatocellular carci-

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Fig. 3. Metastatic endocrine tumor. A CEUS in the arterial phase demonstrates a hypervascular focal liver lesion (arrow) in the right hepatic lobe. B CEUS in the sinusoidal phase displays the focal liver lesion as hypoechoic (arrow) to adjacent hepatic parenchyma.

nomas that were isoechoic and hyperechoic, respectively, in the sinusoidal phase were considered FN (Fig. 5). During the sinusoidal phase of CEUS, the hypoechogenicity of the examined focal liver lesion allowed the diagnosis of malignancy with a sensitivity of 85%, specificity of 88%, positive predictive value of 92%, negative predictive value of 77%, and diagnostic accuracy of 86%. Excluding hepatocellular carcinomas, most of which showed onset with chronic liver disease, lesion hypoechogenicity in the sinusoidal phase at CEUS allowed a diagnosis of malignancy with a 100% sensitivity, 88%

Fig. 4. Hepatocellular carcinoma. A US shows a hypoechoic focal liver lesion (asterisk) in the right hepatic lobe. B CEUS in the arterial phase displays intense enhancement of the focal liver lesion (arrow). C CEUS in the sinusoidal phase shows the focal liver lesion as hypoechoic (arrow) to adjacent hepatic parenchyma.

specificity, 82% positive predictive value, 100% negative predictive value, and 92% diagnostic accuracy.

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b Fig. 5. Hepatocellular carcinoma. A US demonstrates a small hypoechoic focal liver lesion (arrow) in the right hepatic lobe. B CEUS in the arterial phase displays moderate enhancement of the focal liver lesion (arrow). C CEUS in the sinusoidal phase shows the focal liver lesion as isoechoic with adjacent hepatic parenchyma.

The diagnostic confidence in the diagnosis of malignancy on the basis of the hypoechogenicity of the examined focal liver lesions in the sinusoidal phase of CEUS significantly increased, with areas under the receiver operating characteristic curve increasing from 0.536 for baseline US to 0.902 for the sinusoidal phase of CEUS (Fig. 6).

Discussion The use of contrast medium has been shown to improve the diagnostic performance of baseline US study of focal liver lesions [2, 3, 12–16]. The sinusoidal phase of CEUS with sulfur hexafluoride-filled microbubble contrast agent, so called because the microbubbles fill in the sinusoids [12], starts at 120 s and ends at approximately 240 to 360 s. This phase is used for malignant focal liver detection because of the possibility of studying the entire liver parenchyma. During the sinusoidal phase of CEUS, insonation of the entire liver parenchyma is also possible after contrast-enhanced study of hepatic or extrahepatic abdominal tumors such as pancreatic or renal tumors [17, 18]. In the arterial and portal venous phases, only a single lesion, hepatic or primitive extrahepatic, can be studied for 120 s; after contrast medium injection, the entire liver parenchyma can be searched for additional or metastatic focal lesions for an additional 2 min. In the sinusoidal phase of CEUS, lesions with a vascular structure may be derived from neoangiogenesis, and thus have no sinusoidal vessels and do not allow microbubble fill-in, as opposed to the normal parenchyma. All malignant liver lesions should therefore appear as a ‘‘clear defect’’ [11] in the liver parenchyma, which is homogeneously hyperechoic due to microbubble fill-in in the sinusoidal phase of CEUS. In our series, a diagnosis of malignancy, based on the presence of a clear hypoechoic defect in the sinusoidal phase (Fig. 3), was possible in 108 of 127 (85%) of the focal malignant lesions examined. Therefore, not all malignant lesions appear hypoechoic in the sinusoidal phase of CEUS. In our series 19 of 87 (22%) hepatocellular carcinomas were isoechoic or hyperechoic in the sinusoidal phase (Fig. 5). All these lesions were hepatocellular carcinomas against a cirrhotic background. The sinusoidal phase of CEUS presents some limitations in the evaluation of the cirrhotic liver [19]. Liver parenchyma arterialization with sinusoidal capillaries and architectural distortion of the

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Fig. 6. Receiver operating characteristic curves of baseline US and CEUS in the sinusoidal phase in the characterization of 200 focal liver lesions to distinguish benignancy from malignancy.

parenchyma with marked caliber decrease in sinusoids justify the decreased accumulation of microbubbles in the sinusoidal phase in cirrhosis. Moreover, a minority of hepatocellular carcinomas tends to maintain the original sinusoidal architecture, particularly the well-differentiated forms, as reported by immunohistochemical studies [20]. In our series, 22% of hepatocellular carcinomas appeared isoechoic or hyperechoic in relation to the liver parenchyma in the sinusoidal phase (Fig. 5). Similar results have been reported in the literature [14, 21, 22]. As a consequence, the accuracy of hepatocellular carcinoma detection in cirrhosis during the sinusoidal phase of CEUS can be poor. In contrast, in this study all hypervascular metastases were clearly hypoechoic in the sinusoidal phase (Fig. 3). The accuracy of the sinusoidal phase of CEUS in the detection of hypervascular liver metastases has been described [17]. Microbubbles fill in hepatic hemangiomas due to the presence of large vascular spaces. In the sinusoidal phase of CEUS, hepatic lesions with a vascular structure similar to that of the liver, such as focal nodular hyperplasia

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and adenoma, allow a microbubble fill-in similar to that of the normal liver parenchyma. In our series, a diagnosis of benignancy, when a clear hypoechoic defect in the sinusoidal phase was absent, was possible in 64 of 73 (88%) benign focal liver lesions. Therefore some benign liver lesions were hypoechoic in the sinusoidal contrastenhanced phase. Benign lesions with rich fibrotic or necrotic components can appear as hypoechoic in the sinusoidal phase of CEUS. In our series, two sclerotic hemangiomas and two areas of intrahepatic necrosis were erroneously diagnosed as malignant lesions. Conversely, the variable amount of intralesional terminal vascular structures, such as venous spaces or sinusoids [23–25] in adenomas and focal nodular hyperplasias, could explain the appearance of these lesions in the sinusoidal phase [14, 26, 27]. In one case of focal nodular hyperplasia in our series, the particular vascular structure of the lesion at pathology explained the hypoechogenicity of the lesion at CEUS during the sinusoidal phase (Fig. 1). This case was a false positive for malignancy. Immunohistochemical study of the vascularization of this lesion, which demonstrated few sinusoidal vessels with a large number of vascular structures positive for CD34 (Fig. 1D), depicted an arterial vascular network similar to that of hepatocellular carcinoma. When performing CEUS study, this type of focal nodular hyperplasia with atypical vascularization should be considered. CEUS is currently used to characterize pancreatic [17] and renal [18] tumors. Among the advantages of the sinusoidal phase of CEUS, it has to be remembered that this phase allows evaluation of the entire liver parenchyma after examination of the pancreas or kidney has been completed. We did not perform an objective analysis of lesional enhancement during the sinusoidal phase (e.g., computer-assisted image analysis), and this may represent a limitation of the study. However, as in everyday clinical practice, in this study we wanted to assess the value of a subjective evaluation of the features of focal liver lesions in the sinusoidal phase of CEUS. Our results and those of others [28] support the high accuracy of the sinusoidal phase of CEUS in the discrimination between benign and malignant focal liver lesions.

Conclusions The sinusoidal phase of CEUS has a diagnostic accuracy of approximately 85% in the distinction between benign and malignant solid focal liver lesions, with a significant increase in diagnostic confidence compared with baseline US. References 1. Harvey CJ, Albrecht T (2001) Ultrasound of focal liver lesions. Eur Radiol 11:1578–1593

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