Hepatic angiomyolipoma (HAML) is a rare mesenchymal neoplasm that belongs to the perivascular epithelioid tumor family. Though it is characteristically, a triphasic tumor composed of smooth muscle, blood vessels, and adipocytes, the smooth muscle cells are often epithelioid and can represent the near-entirety of the tumor. A HAML composed predominantly of epithelioid smooth muscle cells occurring in the liver presents significant diagnostic challenges as many liver tumors are composed of large epithelioid cells. Furthermore, even if the tumor is not composed predominantly of epithelioid smooth muscle cells, this may be the only component present in a fine-needle aspiration (FNA) or core needle biopsy. A 38-year-old female with a 3 month history of abdominal pain, nausea, and diarrhea was found to have a 12 cm right hepatic lobe mass. FNA biopsy revealed a moderately cellular specimen composed of plump epithelioid cells with indistinct cell borders, low N:C ratio, round to oval nuclei, fine chromatin, occasional nucleoli, and abundant vacuolated to fibrillary cytoplasm. Rare intranuclear inclusions and occasional foamy macrophages were noted. Concurrent core biopsy revealed large polygonal cells with eccentric nuclei and clear, vacuolated to granular, eosinophilic cytoplasm that stained strongly for HMB45, confirming the diagnosis of HAML. Because HAML is a rare tumor, this diagnosis can be easily overlooked; cognizance of the typical cytologic, histologic, and immunophenotypic findings is crucial to establishing a diagnosis.

BACKGROUND: Hepatic angiomyolipoma (HAML) is a rare mesenchymal liver tumour which belongs to the family of perivascular epithelioid cell tumours (PEComas). It is typically composed of blood vessels, smooth muscle, and adipose cells, and shows strong immunoreactivity for HMB-45.
UNASSIGNED: A 57-year-old woman was referred to our hospital with an unclear liver lesion. A fine needle biopsy revealed a suspicion of hepatic angiomyolipoma with extramedullary haematopoiesis. Preoperative imaging revealed a tumour 17 cm in diameter in the left liver lobe segments II and III. A lobectomy of the left lobe segments II and III was performed. The pathological diagnosis of hepatic angiomyolipoma was obtained.
CONCLUSIONS: Variations in the predominance of the tissue components in HAML impedes diagnosis based on imaging alone. The most promising evidence of HAML is the histological identification of lipomatous, myomatous, and angiomatous tissue combined with immunohistochemical positivity for HMB-45. Although the tumour is considered benign, some cases have been described with malignant behaviour. Surgical resection should be considered in case of symptoms, inconclusive biopsy, or growth in follow-up. Other surgical indications may include aggressive patterns such as vascular invasion, p53 immunoreactivity, or rapidly proliferating tumour cells.
CONCLUSIONS: HAML is a rare liver tumour. In patients with symptoms, uncertain diagnosis, or tumour growth, surgical resection should be performed according to oncological criteria.