Liver & intrahepatic bile ducts
Benign / nonneoplastic

Topic Completed: 1 February 2002

Minor changes: 1 August 2020

Revised: 24 January 2019, last major update February 2012

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Angiomyolipoma[TI] liver[TI]

Deepali Jain, M.D.
Page views in 2019: 2,142
Page views in 2020 to date: 1,196
Cite this page: Jain D. Angiomyolipoma. website. Accessed August 10th, 2020.
Definition / general
  • Mesenchymal tumor arising from perivascular epithelioid cells (PEC)
  • Smooth muscle HMB45+ is defining and consistent feature; similar histologically to renal angiomyolipoma but no proven association
  • Myoid and vascular components are clonal; adipose tissue component may be reactive
  • Other lesions derived from PEC (PEComas) include lymphangioleiomyoma, clear cell (sugar) tumor of lung and rare myomelanocytic tumors
  • Approximately 200 cases reported through 2004
  • Often misdiagnosed as lipoma, hepatocellular adenoma or carcinoma, sarcoma, other metastatic neoplasms (Am J Surg Pathol 1999;23:34 [review])
Clinical features
  • Liver is #2 site for AML after kidney
  • Mean age 50 years, range 9 - 79 years; 80% women
  • Only 6 - 10% associated with tuberous sclerosis, these cases are associated with renal AML and may be multiple
  • Similar gene expression profile as hepatic stellate cells and stem cells (Hum Pathol 2005;36:341, Mol Med 2007;13:160)
Case reports
Gross description
  • Well circumscribed but not encapsulated, typically solitary masses up to 20 cm (1 - 36 cm), yellow gray white
  • Necrosis present in larger tumors, may contain hemorrhage, background liver is normal
Gross images

Images hosted on other servers:

Large lobulated tumor with areas containing fat (Figure 10b)

Microscopic (histologic) description
  • Mature adipose tissue, smooth muscle cells and thick walled blood vessels with loss of elastic lamina
  • Spindle cells radiate from walls
  • Extramedullary hematopoiesis in 40%; represents hematopoietic function of liver
  • Smooth muscle cells are epithelioid or spindled with clear (spider web appearance) or eosinophilic cytoplasm or pleomorphic
  • Mast cells common
  • Occasional features are cellularity, nuclear pleomorphism with intranuclear inclusions, tumor giant cells
  • No / rare mitotic figures
  • Most cases have mixed patterns; unusual patterns are angiomatous, inflammatory, lipomatous (70%+ fat), myomatous, oncocytic, pelioid, trabecular
  • Inflammatory subtype resembles inflammatory myofibroblastic tumor or follicular dendritic cell tumor (Ann Diagn Pathol 2010;14:240); trabecular variant mimics hepatocellular carcinoma
  • Malignant cases recur / metastasize; definite criteria for malignancy not established; features associated with malignancy are: large size (10 cm+), increased mitoses (2 - 5/HPF), coagulative necrosis, vascular invasion, CD117 weak / negative (Am J Surg Pathol 2008;32:793)
Microscopic (histologic) images

Images hosted on other servers:


Smooth muscle, vessels, adipose (Figure 10c)

H&E and stains

Positive stains
Negative stains
Electron microscopy description
  • Epithelioid myoid cells have premelanosomes, numerous mitochondria, abundant rough endoplasmic reticulum, glycogen, tight junctions and basal lamina but no thick filaments
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