Hepatic angiomyolipoma (AML) is an uncommon benign hamartomatous hepatic mass lesion, containing blood vessel (angioid), smooth muscle (myoid) and mature fat (lipoid) components. There is an association with tuberous sclerosis, although this is less strong than for renal AMLs.
Most cases of angiomyolipoma are detected incidentally. However acute abdominal pain related to intratumoral haemorrhage and intraperitoneal haemorrhage has been reported ref needed.
Pathologically, an AML is an unencapsulated lesion with vascular, smooth muscle and mature fat components. Angiomyolipoma fat content can vary from less than 10% to more than 95%. Fat component is made up of mature yellow fat cells. At microscopic examination, epithelioid smooth muscle cell and proliferating blood vessels are visible.
It may be classified histologically according to the amount of fat content into several subtypes 3:
- lipomatous (>70% fat)
- myomatous (<10% fat)
Immunohistochemical staining of the tumour cells reveals HMB-45 positivity. Among hepatic tumours, HMB-45 reactivity is found exclusively in the smooth muscle cells AML 7.
There is a reported correlation between hepatic angiomyolipoma and tuberous sclerosis (TS), although the association is not as strong at it is for renal AMLs. Up to 20% of renal AMLs are associated with TS, compared to only 6% of hepatic AMLs 5. Nonetheless, the liver is the second most frequent site of angiomyolipoma after kidney.
Angiomyolipomas may be single or multiple, round or lobulated fat-containing mass lesions, seen more commonly in the right hepatic lobe ref.
The characteristic findings on any modality are the presence of both fat and prominent vascularity in the same lesion. If the fatty component predominates, it resembles lipomas but most of the time, a mixture of usual solid soft tissue intermingled with fatty components will be seen. Conversely, in cases of less fatty content and excess vascular part, the lesion seems like hypervascular hepatic mass lesions.
The drainage vein of AML is the hepatic vein, and identifying a perfusing vein communicating with the hepatic vein from the tumour centre can aid in differentiating AML from fat-containing hepatocellular carcinoma (HCC) 2,4.
Hetero or homogenous echogenic (due to fat content) mass lesion in the right hepatic lobe. In case of less fat content and excess vascular component, angiomyolipoma can be seen as a heterogeneous hypoechoic mass lesion. Could be indistinguishable from a hemangioma 1.
On non-enhanced CT, angiomyolipoma presents as well defined solid heterogeneous mass containing markedly hypodense area. Due to the presence of the vascular component, marked enhancement in arterial phase is evident. Drainage is via the hepatic veins, and this is the main differentiating point from fat-containing HCC that drains mainly in the portal vein.
- well-defined mass with heterogeneous attenuation values due to the presence of fat and soft tissue densities
- may be predominantly low-density mass
- arterial phase: significant enhancement in the arterial phase
- portal phase: becomes hypoattenuated
On MRI the lesion shows hyperintensity like as fatty tissue on both T1 and T2, which decreases with fat suppression. To detect small volume of fat content in cases of lipid-poor AML, chemical shift imaging (i.e. in-phase / out-of-phase) is useful.
- fatty components show hyperintensity on T1WI
- loss of signal on fat suppress sequences
- in cases of poor lipid-content in phase/out of phase will show loss of signal at out of phase
- T2: fatty components show hyperintensity on T2WI
- C+ (Gd): enhancement of vascular component in arterial phase
Treatment and prognosis
Observation is the method of choice for asymptomatic cases. However, cases with severe abdominal pain or intraperitoneal bleeding not responding to conservative treatment can be treated successfully with embolization and/or surgical resection.
General imaging differential considerations include:
hepatocellular carcinoma (HCC) with a fatty component
- typically the fatty content is minimal and is in a scattered pattern
- AFP is elevated and HMB-45 in cell staining is negative
focal fatty infiltration
- poorly defined borders without pressure effect on adjacent vessels
- may be indistinguishable on ultrasound
- very uncommon
- should contain no soft tissue component and never shows enhancement after contrast administration
- metastasis from liposarcoma/teratoma
- extremely uncommon
- 1. Prasad SR, Wang H, Rosas H et-al. Fat-containing lesions of the liver: radiologic-pathologic correlation. Radiographics. 25 (2): 321-31. doi:10.1148/rg.252045083 - Pubmed citation
- 2. Haaga JR, Boll D. CT and MRI of the whole body. Mosby. (2009) ISBN:0323053750. Read it at Google Books - Find it at Amazon
- 3. Prasad SR, Wang H, Rosas H et-al. Fat-containing lesions of the liver: radiologic-pathologic correlation. Radiographics. 25 (2): 321-31. doi:10.1148/rg.252045083 - Pubmed citation
- 4. Zheng RQ, Kudo M. Hepatic angiomyolipoma: identification of an efferent vessel to be hepatic vein by contrast-enhanced harmonic ultrasound. Br J Radiol. 2005;78 (934): 956-60. doi:10.1259/bjr/27365821 - Pubmed citation
- 5. Cha I, Cartwright D, Guis M et-al. Angiomyolipoma of the liver in fine-needle aspiration biopsies: its distinction from hepatocellular carcinoma. Cancer. 1999;87 (1): 25-30. Pubmed citation
- 6. Fricke BL, Donnelly LF, Casper KA et-al. Frequency and imaging appearance of hepatic angiomyolipomas in pediatric and adult patients with tuberous sclerosis. AJR Am J Roentgenol. 2004;182 (4): 1027-30. doi:10.2214/ajr.182.4.1821027 - Pubmed citation
- 7. Nonomura A, Mizukami Y, Takayanagi N et-al. Immunohistochemical study of hepatic angiomyolipoma. Pathol. Int. 2000;46 (1): 24-32. Pubmed citation
- depositional disorders
- infection and inflammation
- liver abscess
- hepatic hydatid infection
- liver and intrahepatic bile duct tumours
- benign epithelial tumours
- hepatocellular hyperplasia
- hepatocellular adenoma
- hepatic/biliary cysts
- benign nonepithelial tumours
- primary malignant epithelial tumours
- primary malignant nonepithelial tumours
- haematopoietic and lymphoid tumours
- secondary tumours
- adrenal rest tumours
- hepatic carcinosarcoma
- hepatic fibroma
- hepatic Kaposi sarcoma
- hepatic lipoma
- hepatic mesenchymal hamartoma
- hepatic myxoma
- hepatic rhabdoid tumour
- hepatic solitary fibrous tumour
- hepatic teratoma
- hepatic yolk sac tumour
- inflammatory myofibroblastic tumour (inflammatory pseudotumor)
- nodular regenerative hyperplasia
- pancreatic rest tumours
- primary hepatic carcinoid
- benign epithelial tumours
- extrahepatic bile duct tumours
- liver and intrahepatic bile duct tumours
- portal venous gas
- portal hypertension
- portal vein thrombosis
- arterioportal shunts
- hereditary haemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)
- Budd-Chiari syndrome
- passive hepatic congestion
- hepatic veno-occlusive disease
- hepatic infarction
- peliosis hepatis
- hepatic venous malformations (haemangiomas)