Hepatic angiomyolipoma: differential diagnosis from other liver tumors in a special reference to vascular imaging - importance of early drainage vein
© Yoshioka; licensee Springer. 2015
Received: 22 September 2014
Accepted: 2 December 2014
Published: 31 January 2015
A 51-year-old female had been diagnosed with a hemangioma in the hepatic segment 6 (S6). After a 6-year follow-up, enlargement of the tumor was detected. The tumor was clearly enhanced in the arterial phase, and the enhancement remained in the portal phase on computed tomography (CT). Although the primary differential diagnosis on CT was hepatocellular carcinoma (HCC), we worried about the possibility of other vessel system tumors because the tumor remained to be enhanced at the portal phase for HCC and all tumor markers of HCC were negative. We performed angiography to determine the tumor nature and to seek other tumors. Angiography showed tumor stain at the hepatic S6 with an early obvious drainage vein from the tumor flowing through the right hepatic vein into the inferior vena cava. In addition to tumor stain and the drainage vein, there were many small poolings of contrast medium in the whole liver, which were suspected as dilatation of the hepatic peripheral artery. We suspected the tumor as a benign tumor such as hepatocellular adenoma or focal nodular hyperplasia, but the possibility of HCC could not be ruled out. Hepatic posterior sectionectomy was done to completely remove the drainage vein with the tumor. Intraoperative histological examination revealed the tumor as not malignant and not HCC. Later, immunohistochemical analysis uncovered that the tumor had high expression of HMB-45 and, therefore, the final diagnosis was angiomyolipoma. We think that detecting an early drainage vein from the tumor would be a key point for diagnosing hepatic angiomyolipoma.
Angiomyolipoma (AML) is a rare benign mesenchymal neoplasm most often arising in the kidney, and extrarenal AMLs are uncommon. Among these extrarenal sites, the liver is the most common site . The appearance in other sites is extremely rare [2,3]. AML is composed of heterogeneous mixtures of smooth muscle cells, mature adipose tissues, thick-walled blood vessels, with occasional foci of extramedullary hematopoiesis [4-8]. Histological diagnosis is performed by immunohistochemical staining against melanoma-associated antigen (HMB-45) . However, hepatic angiomyolipoma (HAML) has usually been misdiagnosed as hepatocellular carcinoma (HCC) with a frequency of more than 50% due to significant overlap of the imaging features [10-13]. Differential diagnosis between HAML and HCC is very important because their prognosis is strikingly different. In some reports, early venous drainage from the tumor is a useful feature for differentiating HAML from HCC [14-18]. If early venous drainage from the tumor is detected preoperatively, it would be helpful for diagnosing HAML.
We here report a case of HAML showing an early venous drainage from the tumor to the hepatic vein detected by angiography preoperatively and review the reported cases having early venous drainage in a special reference to the early drainage veins and its detection modalities.
Laboratory data on admission
405 × 104/mm3
16.6 × 104/mm3
In the literature describing the preoperative diagnosis of HAML [10,13,21-25], the findings are as follows: (1) hypervascular imaging; (2) fatty component on CT, MRI, and US, which shows hyperechoic lesion on US, low attenuation with a density of less than −20 Hounsfield units on CT, and hyperintensity on both T1- and T2-weighted sequences of MRI; (3) positive actin and HMB-45 stains on biopsy specimen. However, differential diagnosis of HAML from other fat-containing lesions of the liver, especially HCC with fatty metamorphosis, is very difficult . The proportion of fatty tissue in HAML varies greatly, ranging from 5% to 90% . This variety would influence the images of MRI. In the present case, both in-phase and out-of-phase images showed similar low intensity, probably due to non-rich fat component and made our diagnosis shift to other tumors than HAML. In fact, misdiagnosis occurs at a frequency of more than 50% due to a significant overlap of the features of imaging in HAML and HCC [10-13]. Other tumors abounding with blood vessels, such as hemangioma, focal nodular hyperplasia, or hepatic adenoma, showing resembling imaging features, are also difficult in differential diagnosis.
Reported cases having early drainage vein in hepatic angiomyolipoma
Number of cases
1. Murakami 
2. Yoshimura 
3. Zheng 
DSA, CED, US
4. Jeon 
5. Iwao 
6. Wang 
Not described a
7. Present case
Here, we must be careful for an AP shunting that is often seen in angiogenic liver tumors. The AP shunts are reportedly rather frequently found in hemangiomas as well, especially in that with rapid enhancement . They are, however, usually depicted as a wedge-shaped or irregularly shaped parenchymal fuzzy enhancement adjacent to the tumor in the hepatic arterial phase of dynamic CT. This CT feature is different from that of the early drainage vein discussed above and may be useful to distinguish them. Although rare, there are some reports of HAMLs with occasional association of AP shunts, too (one case reported by Saito et al.  and three cases by Jeon et al. ). But it is necessary to differentiate AP shunts from the early drainage vein. Concerning the detection modality for an early drainage vein, the usefulness of dynamic MDCT is reported [17,18]. In our case, we first noticed the drainage vein during angiography, but careful image reading of dynamic MDCT could confirm it.
Regarding the multiple small poolings of contrast medium scattered in the whole liver during angiography in our patient, the similar phenomenon has been reported . The lesions of the case report were diagnosed as multiple hemangiomas by surgery, but in our patient, the liver looked normal macroscopically and no hemangiomas were detected in the resected specimen either macroscopically or histopathologically. In addition, we could not find any micro HAML or the lesion that might be tentatively expressed as a bud of HAML. Therefore, it may be too hasty to conclude that these multiple small poolings of contrast medium are indubitably small hemangiomas. AML occurs frequently in the kidney, where it is closely related to tuberous sclerosis [28,29]. Tuberous sclerosis is an autosomal dominant genetic disorder that arises from germ line mutations in TSC1 or TSC2, which encode hamartin and tuberin, respectively [30,31]. In tuberous sclerosis patients, abnormality in blood vessels occasionally happens, such as aneurysms or narrowing of blood vessels. Therefore, we examined the expression of TSC1/hamartin in the tumor in the protein level immunohistochemically to address the mystery of the multiple small poolings of contrast medium. The expression of TSC1/hamartin was reduced in the tumor tissue in comparison with the surrounding liver tissue. This result might show a possible relationship of the HAML tumor with decreased TSC1/hamartin expression in this patient but did not answer the abnormal poolings of contrast medium in the surrounding liver tissue during angiography. Close follow-up of the patient for the recurrence of nodules is required, and the reproducibility of the same abnormal poolings in future imagings is intriguing.
Lastly, there are some reports of malignant HAML. Deng et al. reported malignant characteristics as marked cell atypia, vascular invasion, high proliferation activity (Ki67 index above 30%), and large tumor size . In the present case, precise pathological examination revealed a tumor infiltration into the hepatic vein although the tumor was negative for FDG-PET and low in the Ki67 index. It is uncertain whether this finding of vascular invasion directly suggests the malignant transformation of this tumor or not , but preoperative detection of such a minute finding is dubious even by means of biopsy. Conservative management of the tumor that is diagnosed as HAML should be careful and will be recommended only in the condition of close follow-up, otherwise surgical resection is recommended.
We presented a case of HAML with early drainage vein flowing to the hepatic vein. We think that detecting an early drainage vein would be a key to diagnose the HAML. In case an obvious drainage vein is detected, HALM will come to the very front line of differential diagnosis.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
This case report is not supported by any grants.
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