British Journal of Radiology (2005) 78, 956-960
© 2005 British Institute of Radiology
doi: 10.1259/bjr/27365821
Hepatic angiomyolipoma: identification of an efferent vessel to be hepatic vein by contrast-enhanced harmonic ultrasound
R Q Zheng, MD, PhD1 and
M Kudo, MD, PhD2
1 Department of Ultrasound, the Third Affiliated Hospital, Sun Yat-sen University, Shipai, Guangzhou 510630, China and 2 Department of Gastroenterology and Hepatology, Kinki University School of Medicine, Osaka-Sayama, Japan
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Abstract
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We report two patients with rare hepatic angiomyolipoma and demonstrate the special tumour haemodynamics with contrast-enhanced harmonic ultrasound. This reliably identified the efferent vessel of the hepatic angiomyolipoma to be the hepatic vein in both cases, which corresponded well with that seen on conventional angiography and CT angiography. This haemodynamic finding may be an important characteristic of hepatic angiomyolipoma, and facilitate the differential diagnosis from other benign and malignant hepatic tumours.
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Introduction
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Hepatic angiomyolipoma is an extremely rare benign tumour of the liver [1]. With the progress of imaging modalities including CT, MRI and ultrasound (US), the reports have been increasing [1–4]. However, to our knowledge, no reports using contrast-enhanced harmonic US to evaluate tumour haemodynamics of hepatic angiomyolipoma have been published. A single case report [4] using ordinary power Doppler had limitations in depicting tumour vessels. Herein, we report two cases of hepatic angiomyolipoma and demonstrate their special tumour haemodynamics with contrast-enhanced harmonic US.
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Case reports
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Two patients with liver mass detected by US and/or CT incidentally were admitted to our hospital. Physical examinations, all routine blood examinations and tumour markers including 
-fetoprotein (AFP), prothrombin-induced vitamin K absence (PIVKA-II) of both patients were normal at the time of admission. The imaging features of the two patients are described below.
Case 1, female, 43 years
Abdominal US of a 43-year-old female revealed a heterogeneous hypoechoic nodule mixed with hyperechoic area with an irregular shape and poorly defined margin in the medial segment of the liver (Figure 1a
). Colour and power Doppler showed abundant blood signals within the tumour. Contrast-enhanced harmonic US was performed using the Coded Harmonic Angio mode in LOGIQ 700 EXPERT (General Electric Medical System, New York, NY) after administration of an intravenous contrast agent, Levovist (Schering AG, Berlin, Germany). The early arterial phase performed in real time scanning demonstrated tumour vessels, including tumour feeding vessel (Figure 1b). During the late vascular phase, tumour parenchymal stain of the whole nodule was revealed and an efferent vessel was clearly demonstrated flowing from the tumour continuously to the hepatic vein (Figure 1c–f). Contrast-enhanced three-phase dynamic CT revealed a high-attenuation lesion in the arterial phase and portal venous phase, and iso-attenuation in the delayed phase with an irregular shape. The mass was demonstrated as hypervascular on CT during arteriography (CTA) and tumour perfusion defect on CT during arterial portography (CTAP). On MRI with superparamagnetic iron oxide (SPIO) enhancement, the tumour was observed as a heterogeneous hyperintensity mass. Digital subtraction angiography (DSA) of the liver demonstrated an irregular hypervascular mass with early venous drainage in the venous phase (Figure 1g); the hepatic vein being the efferent vein of the tumour. Hepatic angiogram also demonstrated multiple small pooling within the liver suggesting multiple small haemangiomas (Figure 1g).
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Figure 1. 43-year-old woman with a histology-proven hepatic angiomyolipoma. (a) Fundamental B-mode ultrasound (US) revealed a heterogeneous hypoechoic nodule mixed with hyperechoic areas in the medial segment of the liver (arrows). The lesion was irregular in shape with ill-defined margin. After Levovist administration using Coded Harmonic Angio mode, (b) tumour vessels, including the feeding vessel (arrows), were demonstrated in the early arterial phase. During the late vascular phase, (c) tumour parenchymal stain of the whole nodule was apparent (arrow). (d) An efferent vessel appeared in the inferior margin of the tumour (arrow) and (e, f) continued to a hepatic vein during dynamic assessment (arrows). ) (g) Digital subtraction angiography in the venous phase showed the dense stain of the nodule and the efferent vessel, which was the hepatic vein (arrows). In addition, multiple small haemangiomas were also shown. (h) The cut surface of the ill defined tumour was yellowish mixed with white colour tissue and dark haemorrhage clot. (i) On histological section, a small thick-walled vessel (arrows) surrounded by proliferated tumour cells was seen.
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According to the imaging characteristics of this nodule, namely a hypervascular nodule with hepatic vein as the efferent vein of the tumour, a benign hypervascular tumour of the liver, either a hepatic adenoma or angiomyolipoma were suspected. The patient underwent surgery for tumour resection with informed consent. The cut surface of the tumour was yellowish mixed with white coloured tissue and foci of haemorrhagic clot (Figure 1h
). The mass was ill defined with no fibrous capsule. The surrounding tissues were normal. On operation, multiple small haemangiomas of the liver were also identified. Histologically, there were big vessels and many small thick-walled vessels surrounded by proliferated spindle-shaped tumour cells (Figure 1i), which showed strongly positive for HMB-45 immunohistochemical stain and muscle-specific actin stain. Pathological diagnosis of hepatic angiomyolipoma was confirmed. However, the component of adipose tissue within the tumour was extremely sparse.
Case 2, female, 49 years
Abdominal US of a 49-year-old female showed a heterogeneous isoechoic lesion mixed with small hypoechoic areas in the posterior superior area of the right liver. The mass was 6 cm in diameter with ill-defined margins. Colour and power Doppler US showed abundant blood signals within the tumour. Contrast-enhanced harmonic colour and power Doppler US revealed a hypervascular mass, and also clearly showed the drainage vessel from inside the tumour through the hepatic vein flowing to the direction of the inferior vena cava (IVC) (Figure 2a). Dynamic CT revealed an inhomogeneous high-attenuation lesion in the arterial phase and portal venous phase with iso-attenuation in the delayed phase. CTA demonstrated a hypervascular mass and clearly showed the afferent and efferent vessels of the tumour. The tumour efferent vessel was hepatic vein and flowed directly to the IVC (Figure 2b). On CTAP, the tumour was depicted as hypoattenuating mass. MRI with T1 and T2 weighted sequences as well as SPIO enhancement all revealed a heterogeneous hyperintensity mass. DSA also demonstrated a hypervascular mass and showed the hepatic vein as the tumour efferent vein draining into the IVC. According to the imaging and clinical features of this patient, malignant liver tumours were not suspected, while benign hypervascular tumours including hepatic adenoma were considered. Because of a big tumour with the risk of spontaneous rupture and bleeding, the patient underwent tumour resection following informed consent. The tumour was found to be 6.8 cm x 5.5 cm in size, and a branch of right hepatic vein at the edge of the tumour was identified on operation.
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Figure 2. 49-year-old woman with a histology-proven hepatic angiomyolipoma. (a) Contrast-enhanced harmonic power Doppler ultrasound revealed a hypervascular mass with strong tumour parenchymal stain in the posterior superior segment of the right liver lobe. An efferent vessel that ran from inside the tumour via the right hepatic vein to the direction of inferior vena cava (IVC) was seen (arrow). (b) On CT during angiography, a hyperdense mass with afferent (white arrow) and efferent (black arrow) vessels was clearly demonstrated. The efferent vessel was the hepatic vein that flowed from the tumour into the IVC through right hepatic vein, consistent with the finding revealed by contrast-enhanced harmonic power Doppler.
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The cut surface of the mass was dark reddish with a focus of haemorrhagic area. It had a well-defined margin with no capsule. Histologically, there were many thick-walled and thin-walled vessels inside the tumour. Although there were few obvious mature fatty tissue cells within the tumour section, most of the myogenic cells were positive for HMB-45 stain, leading to the final diagnosis of hepatic angiomyolipoma.
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Discussion
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Histologically, hepatic angiomyolipoma is characterized by a mixture of mature fat cells, blood vessels and smooth muscle cells in various proportions. It used to be diagnosed post-operatively or by autopsy [1, 2]. However, with the progress of imaging techniques, it has been reported more frequently by demonstrating both the fatty and vascular components within the tumour pre-operatively [1–3]. Nevertheless, the differential diagnosis with other liver tumours, especially malignant tumours, still remains difficult [1].
According to the relevant literature [1–7], hepatic angiomyolipoma can be diagnosed pre-operatively according to the following findings: (1) hypervascular nature on imaging suggesting vascular proliferation within the tumour. (2) Imaging findings of fatty component on CT, MRI and US, which manifests as hyperechoic on US, low attenuation with a density of less than –20 Hounsfield units (HU) on CT and hyperintense on both T1 and T2 weighted sequences of MRI. (3) Positive actin and HMB-45 stains on biopsy specimen, which proves smooth muscle component.
However, with only non-invasive imaging methods the differential diagnosis of hepatic angiomyolipoma from other fat-containing lesions of the liver, especially hepatocellular carcinoma (HCC) with fatty metamorphosis, is difficult [1]. Furthermore, the proportions of fatty tissue within the tumour varies greatly, ranging from 5% to 90% [6], leading to variable manifestations and atypical imaging appearances. Both of our cases presented as atypical hypoechoic or isoechoic lesions due to a small proportion of fatty tissue, also encountered in other case reports [3–5]. with such situations, evaluation of the haemodynamic characteristics of a hypervascular tumour might offer useful information to differentiate the tumour from other diseases.
Tumour haemodynamic evaluation is important for the differentiation and pathological assessment of liver tumours [8]. Recently, apart from studying tumour feeding vessels, studies on haemodynamics of tumour draining vessels have been assessed [9]. It has been reported that the portal vein acts as the main drainage vessel of HCC [11, 12], which might explain the phenomenon of portal venous tumour thrombus being more frequent than hepatic venous thrombus [9] and might play an important role in the intrahepatic metastasis of HCC [11]. Tanaka et al [10] reported that colour Doppler could detect constant-flow signals draining from the tumour to the portal venous branches in 10 of the 19 HCCs, but in none of the 9 adenomatous hyperplastic nodules. The differences among various patterns of efferent blood flow may reflect the differences of tumour pathological features. Although angiography, US angiography, CTA and CTAP are the sensitive imaging modalities in demonstrating tumour haemodynamic changes, they are not preferable as routine methods in most clinical settings because of its invasiveness. Fundamental colour and power Doppler are not always satisfactory for evaluating tumour vascularity when compared with dynamic CT, dynamic MR and invasive imaging modalities mentioned above [8]. However, newly developed intravenous contrast-enhanced US has become a promising method in depicting tumour vascularity because of its non-invasiveness and the ability to provide dynamic flow information on a tomographic plane under completely physiological conditions [12, 13].
By using contrast-enhanced harmonic imaging, we could clearly reveal that the efferent vessels of the two hepatic angiomyolipomas were hepatic veins, which were in agreement with the DSA and/or CTA findings. Therefore, the diagnosis of HCC was not considered pre-operatively owing to the haemodynamic characteristics differing from HCC. Hepatic cavernous haemangioma and focal nodular hyperplasia were also ruled out since the haemodynamic features of these two tumours, namely a spotty pooling pattern with gradual fill-in over time in haemangioma and the central arterial blood supply with centrifugal radiation pattern in early arterial phase in focal nodula hyperplasia (FNH) [8, 14], were not demonstrated by imaging modalities. Hepatic adenoma would be the most difficult benign tumour to distinguish from angiomyolipoma. In both of our two cases, the possibility of hepatic adenoma was considered, being hypervascular with nearly the same manifestation on dynamic CT and angiography as an angiomyolipoma. A more regular shape and lack of fatty component in most hepatic adenomas might be helpful for the differentiation. Whether there are any differences in tumour efferent vessels between them remains unknown.
Some early-stage small HCC also show an efferent vessel to be hepatic vein [15]. However, in our cases, the size of the tumours was greater than 3 cm, exceeding the range of small HCC. Furthermore, early and prolonged enhancement on dynamic CT [3] and clinical information including no evidence of liver cirrhosis, negative tumour markers for HCC may help the diagnosis of hepatic angiomyolipoma.
Investigation of tumour drainage vessel may facilitate the differential diagnosis of different tumours. To our knowledge, few reports about tumour efferent vessel except HCC [9–11, 15] had been published. We present here an hepatic vein acting as the efferent vessel of hepatic angiomyolipoma, which can be clearly demonstrated by using non-invasive contrast-enhanced US and CTA. Irregular shape of the mass with no capsule and hepatic vein being the efferent vessel of the tumour might be the characters of hepatic angiomyolipoma, however, whether this haemodynamic character will be the main feature of hepatic angiomyolipoma needs more observations.
Received for publication March 1, 2005.
Revision received March 21, 2005.
Accepted for publication April 15, 2005.
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References
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Abstract
Introduction
