Hepatic Angiomyolipoma: A Case Report

Hepatic angiomyolipoma (AML) is a rare benign tumor with heterogeneous components composed of vascular, fat, and smooth muscle elements which is often misdiagnosed as other neoplasms such as hepatocellular carcinoma due to nonspecific clinical and image features. A typical case of hepatic AML located in liver with overall clinic and ultrasonography information was analyzed and relative references were reviewed in this article.

A 39-year-old woman had an abdominal sonography at local hospital for regular checkup. He had no other illnesses and no remarkable family medical history. The grayscale ultrasonography revealed a 2.7 cm × 2.4 cm sized heterogeneous hyperechoic lesion in segment 7 of liver. She referred to our hospital for further diagnosis and treatment. The color Doppler flow image showed that abundant blood flow signals were found inside and around the lesion (Fig. 1). Then contrast enhanced ultrasound (CEUS) was performed. The contrast agent used in this study was SonoVue (Bracco, Milan, Italy), a sulphur hexafluoride-filled microbubble contrast agent. A total of 2.4 mL of contrast agent was injected into the antecubital vein in a bolus fashion through a 20-gauge intravenous cannula, followed by a flush of 5.0 mL of 0.9% sodium chloride solution. In the arterial phase, the lesion showed homogeneous hyperenhancement 13 s after contrast agent injection, and the blood supply artery was visible around the lesion (Fig. 2). In the portal phase (45 s after contrast agent injection), the lesion showed slight hyperenhancement (Fig. 3). In late phase (120 s after contrast agent injection), the lesion showed isoenhancement (Fig. 4). There was no other specific finding. The laboratory findings of this case showed normal liver function tests, and the tumor marker tests for carbohydrate antigen 19-9, carcinoembryonic antigen, alpha-fetoprotein were all within normal ranges. The tests for hepatitis B and C virus were negative. The impression for the lesion was benign tumor. To identify the lesion's characteristics, she underwent the ultrasound guided liver biopsy. Based on the histologic findings and results of immunohistochemical staining, the final diagnosis was hepatic AML (Fig. 5).

Figure 1
The gray-scale ultrasonography showed a heterogeneous hyperechoic lesion in segment 7 of the liver and vessels were found inside and around the lesion.

Discussion
Angiomyolipoma (AML) is a benign mesenchymal tumor with heterogeneous components composed of vascular, fat, and smooth muscle elements. AML often occurs in the kidney but is rarely found in the liver. Hepatic AML is almost sporadic, but it is associated with tuberous sclerosis complex in some cases [1]. As a benign tumor, rare malignant transformation has been reported. Although the invasive growth of the tumor can occur, the pathological examination cannot be diagnosed as malignant tumor [2]. Most patients with hepatic AML present with no specific symptoms, and some patients may complain of abdominal pain, abdominal distension, fever, discomfort and weight loss [3]. There are no reliable serologic markers to date [4], and no history of viral hepatitis infection in the majority of cases.
According to the inner fat content, AML is classified histologically into mixed, lipomatous, myomatous and angiomatous types. The diagnosis of hepatic AML is still challenging and mainly depends on identification of fat within the tumor on imaging. On gray-scale ultrasonography, hepatic AML may show obvious heperechogenicity because of the fat content. The fat content proportion of hepatic AML varies from <5% to >90% [5]. Thus, the lesion can show homogeneous or heterogeneous hyperechogenicity. On color Doppler flow image, arterial signals can usually be detected around the tumor. Wang et al [6] reported the maximal blood velocity in hepatic AML ranged from 38.3 to 140 cm/s, and the mean resistive index was 0.53 ± 0.1, which was lower than that in hepatocellular carcinoma .
CEUS was demonstrated to be useful in the assessment of tumor vascularization, and it showed that lots of liver lesions showed characteristic enhancement patterns. On real-time CEUS, hepatic AML always show homogeneous or heterogeneous hyperenhancement during the arterial phase, and the enhancement of the lesion was seen earlier than the enhancement of liver parenchyma. In this study, the blood supply artery was visible around the lesion. These features indicated that the hepatic AML was rich in blood supply. During the protal phase and late phase, the hepatic AML showed sustained enhancement (slight hyperenhancement or isoenhancement), which is a critical clue for determining the benign nature of the disease.
Compared with gray-scale ultrasonography, CEUS Figure 2 In the arterial phase of contrast enhanced ultrasound, the lesion showed homogeneous hyperenhancement and the blood supply artery (arrow) was visible around the lesion.

Figure 4
In the late phase of contrast enhanced ultrasound , the lesion showed isoenhancement. improved the diagnostic accuracy of hepatic AML. However, the CEUS enhancement pattern of hepatic AML is not specific, and is difficult to differentiate from the focal nodular hyperplasia, hepatic adenoma and even liver cancer. Thus combining the clinical data with the particular features on ultrasonography and CEUS could lead to an improved diagnosis rate for the disease. The final diagnosis for hepatic AML still depends on the biopsy or surgery.

Conclusion
In conclusion, the hepatic AML shows homogeneous enhancement in the arterial phase and sustained enhancement in the portal or late phase. The CEUS patterns are helpful for diagnosis for hepatic AML. The combination of gray-scale ultrasonography and CEUS leads to an improved diagnosis rate for the disease.