Diagnostic component is spindle or epithelioid smooth muscle cells
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
Nuclear atypia and infiltrative margins can be seen in benign tumors
Ancillary Tests
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Smooth muscle cells stain with antibodies to HMB-45, MART-1, but not keratin or Hep-Par1
Top Differential Diagnoses
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Hepatocellular neoplasm, particularly hepatocellular carcinoma
•
Metastatic malignant tumor, either carcinoma or sarcoma
TERMINOLOGY
Abbreviations
Definitions
•
Rare, benign mesenchymal neoplasm composed of smooth muscle, adipose tissue, and vessels
Thought to arise from perivascular epithelioid cells (PEC); therefore, considered part of PEComa family of tumors
CLINICAL ISSUES
Epidemiology
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Incidence
Rare: Overall incidence unknown but only a few hundred cases reported
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
Adults 17-86 years (mean: 43.5-50 years)
•
Sex
Marked female predominance
Presentation
•
Most patients are asymptomatic and present incidentally
•
Large tumors may cause symptoms related to mass effect or abdominal discomfort
Treatment
•
Surgical approaches
Excision
–
When diagnosis cannot be established on biopsy
–
Large lesions at risk for rupturing
•
Conservative approaches
If diagnosis can be confidently established, radiologic follow-up is recommended
Prognosis
•
Benign behavior in nearly all cases
Tumor recurrence is uncommon
Metastasis extremely rare
IMAGING
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
MACROSCOPIC
General Features
. Note that the background liver is not cirrhotic.
, vessels 
, and myoid cells 
, which in this case are plump and spindled.
of an angiomyolipoma contrasts with the more eosinophilic and granular hepatocyte cytoplasm 
.
at the interface with background liver 
is not an indication of malignancy.
