Diagnostic component is spindle or epithelioid smooth muscle cells

image Epithelioid smooth muscle cells are typically large, with round to oval nuclei, and eosinophilic to fibrillar or vacuolated cytoplasm

• Features that predict malignant behavior are not well defined
image Nuclear atypia and infiltrative margins can be seen in benign tumors

Ancillary Tests

• Smooth muscle cells stain with antibodies to HMB-45, MART-1, but not keratin or Hep-Par1

Top Differential Diagnoses

• Hepatocellular neoplasm, particularly hepatocellular carcinoma

• Metastatic malignant tumor, either carcinoma or sarcoma

• Malignant melanoma

Diagnostic Checklist

• Heterogeneous tumor that contains mixture of plump eosinophilic cells and fat should raise suspicion for angiomyolipoma

Gross Appearance
Gross photograph of a fixed specimen shows a heterogeneous, mottled, tan, yellow, and brown tumor with areas of hemorrhage and degeneration image. Note that the background liver is not cirrhotic.

Admixed Fat, Vessels, and Spindled Myoid Cells
Angiomyolipoma is composed of 3 admixed elements: Adipose tissue image, vessels image, and myoid cells image, which in this case are plump and spindled.

Smooth Muscle Cells
The somewhat amphophilic and fibrillary cytoplasm of the smooth muscle cells image of an angiomyolipoma contrasts with the more eosinophilic and granular hepatocyte cytoplasm image .

Infiltrative Border
The infiltrative growth pattern of this angiomyolipoma image at the interface with background liver image is not an indication of malignancy.



• Angiomyolipoma (AML)


• PEComa


• Rare, benign mesenchymal neoplasm composed of smooth muscle, adipose tissue, and vessels
image Thought to arise from perivascular epithelioid cells (PEC); therefore, considered part of PEComa family of tumors



• Incidence
image Rare: Overall incidence unknown but only a few hundred cases reported

image Some cases associated with tuberous sclerosis (6-10%), but less often than renal AML (20-40%)

– More likely to be associated with tuberous sclerosis if multiple &/or associated with renal tumors

• Age
image Adults 17-86 years (mean: 43.5-50 years)

• Sex
image Marked female predominance


• Most patients are asymptomatic and present incidentally

• Large tumors may cause symptoms related to mass effect or abdominal discomfort

• Tumor rupture is rare


• Surgical approaches
image Excision

– When diagnosis cannot be established on biopsy

– Symptomatic tumors

– Large lesions at risk for rupturing

• Conservative approaches
image If diagnosis can be confidently established, radiologic follow-up is recommended


• Benign behavior in nearly all cases
image Tumor recurrence is uncommon

image Metastasis extremely rare


Ultrasonographic Findings

• Most angiomyolipomas present as heterogeneous hyperechoic lesions, but can be hypoechoic

MR Findings

• MR is most specific imaging modality for detecting lipomatous component

• Most tumors are hypointense on T1WI and slightly hyperintense on T2WI

CT Findings

• Usually hypodense on precontrast CT


General Features

• Usually solitary, occasionally multiple
• Well circumscribed

• Either not encapsulated or only partially encapsulated

• Cut surface is soft and yellow, tan, gray, or brown

image May contain areas of hemorrhage and necrosis

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Apr 20, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Angiomyolipoma

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