Hepatic angiomyolipoma: a series of six cases with emphasis on pathological-radiological correlations and unusual variants diagnosed by core needle biopsy

Abstract

Hepatic angiomyolipoma is rare and may pose differential diagnostic difficulty, particularly if encountered in core needle biopsy. We studied 6 cases from 5 males and one female (median age, 48.6 yrs). All presented with non-specific symptoms or an incidentally discovered tumor mass. Two patients had a remote history of chemotherapy for hematological neoplasms (acute lymphoblastic leukemia and Hodgkin lymphoma respectively) and another had clear cell renal cell carcinoma and anaplastic pancreatic carcinoma diagnosed at autopsy without definable syndrome. None of the patients had evidence of the tuberous sclerosis complex or renal or other extra-renal angiomyolipoma. Three tumors were resected completely and three have been only biopsied and followed up. None of the resected cases recurred at a mean follow-up of 35 months. Histologically, tumors were classified as classical triphasic (1), lipomatous (2), epithelioid/oncocytoid (1), epithelioid trabecular (1) and myelolipoma-like (1). The adjacent liver parenchyma was normal in 3 cases, showed pigment cirrhosis in one case and mild fatty change in another case. One case had clinically diagnosed but histologically unverified cirrhosis. The initial diagnostic impression/frozen section was misleading in 5 of the cases and included vascular lesion, focal fatty change, myelolipoma, hepatocellular tumor and oncocytic neoplasm. All tumors expressed HMB45 and variably desmin. One epithelioid lesion expressed HMB45 and TFE3, but lacked desmin expression. In conclusion, hepatic angiomyolipomas are increasingly recognized as incidental findings during surveillance for cirrhosis or investigations for unrelated conditions. Awareness of their diverse morphological spectrum in liver biopsy is necessary to avoid misdiagnosis as hepatocellular carcinoma, metastatic melanoma or other malignant neoplasms.

Keywords: Angiomyolipoma; HMB45; PEComa; TFE3; liver; myelolipoma.

Figure 1

Large mixed angiomyolipoma of the left liver lobe. Inhomogeneous appearance on contrastenhanced CT with large fatty areas and interspersed dilated vessels (left side) and relatively homogenous soft tissue (smooth muscle) component to the right.

Figure 2

Right: This lipid rich hepatic angiomyolipoma appeared on CT as a well circumscribed hypodense lesion with small isodense streak (arrow) which corresponded to a mixed component on histological examination at autopsy. Left: On ultrasound examination the lesion was round shaped and sharply delineated with a homogenous hyperechoic echotexture.

Figure 3

Multiple well circumscribed round lesions with high SI on both T2-w TSE images with and without fat saturation. The lesions were moderately hyperintense on T1-w images and demonstrate avid enhancement after contrast injection. Vessels can be delineated within the lesions as curvilinear structures. In contrast-enhanced ultrasound, capillary flow can be visualized (lower right panel).

Figure 4

Example of classical (A-E, case 2) and lipomatous (F, case 1) hepatic angiomyolipoma. A. Admixture of fat, thickwalled vessels and smooth muscle cells. B. Prominent dilates sinusoids surrounded by hematopoietic tissue and lymphoid follicles. C. Hematopoietic tissue seen at higher magnification. D. Macrotrabecular growth highlighted by HMb45 immunostaining, note dilated sinusoids bordering macrotrabeculae. E. Entrapment of hepatocytes was common at the periphery of lesions. F. foamy cell aggregates (histiocytes) were prominent in one large fat-rich tumor.

Figure 5

Unusual variants diagnosed by core needle biopsy. A, B: case 4 (inset HMB45 stain). C, D: case 6 (inset: HMB45 stain). E, F: case 5. (Inset in E: HMB45 stain; inset in F: TFE3 stain).

Figure 6

Trabecular hepatic AML (case 3). A. The lesion was well circumscribed peripherally but not encapsulated, note prominent vascularity and absence of thick-walled vessels. B. At higher magnification, note close similarity to HCC. C. Prominent expression of HMB45. D: Melan A (MART-1) stained slender sinusoidal-like cells within adjacent liver tissue (these cells however did not stain with HMB45).