Hepatic angiomyolipoma

Clinical History

A 30-year-old man presented with a 6-month history of vague abdominal discomfort. On examination, mild hepatomegaly was noted. Systemic examination was unremarkable. Ultrasonography revealed a large mixed echotexture, predominantly hyperechoic mass in the right lobe of liver. Liver function tests, routine blood investigations and tumour markers were normal.

Imaging Findings

CT demonstrated a large, relatively well marginated heterogeneously enhancing mass in the right hepatic lobe. The lesion exhibited intralesional markedly low-attenuation areas corresponding to adipose tissue. This fatty component of the mass was confirmed on fat-supressed T1-and T2-weighted MRI. The non-cirrhotic liver displayed no other lesion. Remaining abdomen was normal. In the light of imaging findings and normal tumour markers, diagnostic possibility of angiomyolipoma was considered which was subsequently confirmed histopathologically.

Discussion

Hepatic angiomyolipoma (AML) is a rare, benign, hepatic mesenchymal tumour composed of varying amounts of smooth muscle cells, adipose tissue and blood vessels. The liver is the second most frequent site of involvement preceded by kidneys. Unlike renal AMLs, only 5.8% of patients with hepatic AML have tuberous sclerosis [1, 2].

Hepatic AMLs are most commonly seen in adult female patients, although both genders can be affected. They are frequently detected as an incidental finding at radiological imaging. However, complaints such as abdominal discomfort, pain, distension, fever and weight loss have been reported. Spontaneous rupture and haemorrhage can manifest as acute abdomen.

AMLs display a wide variety of imaging appearances depending on varying proportions of intra-lesional adipose tissue, blood vessels, and smooth muscle cells [1-3]. Intra-tumoral fat component can vary from 10% to 90%. Owing to presence of fat, the tumour is typically hyperechoic on US. The lesion can be homogeneously echogenic or may appear heteroechoic. Colour Doppler sonography may show punctuate or filiform tumoural vascularity. CT or MRI can suggest the possibility of angiomyolipoma by depicting the fatty component of the tumour. Amongst CT and MRI, out-of-phase (chemical shift) MRI has proven valuable in confirming the presence of fat in lesions previously indeterminate at CT. It is, however, important to note that AMLs may be predominantly composed of blood vessels and smooth muscles can and be devoid of any detectable fat on CT or MRI [1, 2]. On dynamic contrast study, AMLs can show avid enhancement on the arterial phase scan. These lesions continue to enhance on the portal venous phase and may show enhancing central vessels. However, it can be quite difficult to distinguish AML from hepatocellular carcinomas with fatty metamorphosis based on contrast enhancement characteristics. Other differential diagnoses of fat-containing liver lesions include hepatic lipoma, angiolipoma, adenoma, focal fatty infiltration, and metastatic neoplasms such as malignant teratoma and liposarcoma. It is vital to remember that radiological findings may only be suggestive of AML; its definitive diagnosis requires histological and immunohistochemical confirmation [1-5].

Surgical resection is the treatment of choice for hepatic AMLs. Conservative management and regular follow-up has been suggested for asymptomatic tumours which are histologically proven, smaller than 5 cm, and occurring in non hepatitis virus carrier patients with good compliance [4, 5].

Differential Diagnosis List

Final Diagnosis

Hepatic angiomyolipoma

URL:	https://www.eurorad.org/case/9083
DOI:	10.1594/EURORAD/CASE.9083
ISSN:	1563-4086