Kidney tumor

Benign adult tumors


Editorial Board Member: Debra L. Zynger, M.D.
Tatjana Antic, M.D.

Last staff update: 2 February 2023 (update in progress)

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PubMed Search: Renal angiomyolipoma

Tatjana Antic, M.D.
Page views in 2022: 37,253
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Cite this page: Antic T. Angiomyolipoma. website. Accessed February 4th, 2023.
Definition / general
  • Member of perivascular epithelioid cell (PEC) tumor family
Essential features
  • Angiomyolipoma, classic variant, is a benign mesenchymal neoplasm composed of admixture of thick dysmorphic blood vessels, smooth muscle and adipose tissue
  • Amount of each component is variable
  • Some cases show significant sclerosis
  • Epithelioid variant has potential to metastasize
  • Angiomyolipoma can occur in extrarenal sites
  • PEComa: perivascular epithelioid cell (PEC) tumor family
ICD coding
  • ICD-O: 8860/0 - angiomyolipoma
  • Presumably arises from perivascular epithelioid cells, which have no known body counterpart
Clinical features
  • Usually asymptomatic in screened tuberous sclerosis patients due to smaller size when discovered
  • May coexist with renal cell carcinoma in nontuberous sclerosis patients, particularly clear cell carcinoma (Mod Pathol 2001;14:157)
  • Tumors can be quite large, multifocal and can extend into the renal vein or vena cava
  • Classic variant is benign but may be complicated by hemorrhage if the tumor is large
  • Routine laboratory within normal limits
Radiology description
  • Characteristic radiologic appearance with fat content in the classic variant
  • Radiologic findings depend on the amount of fat within the tumor (AJR Am J Roentgenol 2017;209:826)
Radiology images

Images hosted on other servers:
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CT with renal mass

Prognostic factors
  • Benign course in angiomyolipoma, classic variant
  • Tumors with epithelioid and pleomorphic features can have a more aggressive course (Mod Pathol 2013;26:1355, Ann Diagn Pathol 2020;47:151538, Urol Oncol 2022;40:18)
  • Sarcomatous transformation with distant metastasis is extremely rare
  • Retroperitoneal hemorrhage is an important complication (Urology 2008;72:1077)
  • Patients with bilateral disease can have renal failure
  • Death can occur due to involvement of contiguous organs particularly blood vessels
Case reports
Gross description
  • Tumor ranges from 0.5 to 25 cm with a mean of 6 cm
  • Circumscribed, not encapsulated with pushing border
  • Cut surface can have red (vascular component), gray-white (smooth muscle component) or yellow (adipose component) appearance
  • May involve the intrarenal venous system, the renal vein or the vena cava despite being benign (Arch Pathol Lab Med 1990;114:65)
  • Tumors rarely have a cystic component (Mod Pathol 2006;19:669)
  • Tumors are usually unilateral and unifocal
  • Multiple (~33%) or bilateral (15%) tumors suggest underlying tuberous sclerosis
Gross images

Contributed by Tatjana Antic, M.D.
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Classic variant

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Predominant adipose tissue

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Fat poor

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Hemorrhagic angiomyolipoma

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Cystic epithelioid angiomyolipoma with hemorrhage

Microscopic (histologic) description
  • Classic triphasic with myoid spindle cells, mature adipose tissue and dysmorphic thick walled blood vessels without elastic lamina
  • Smooth muscle component appears to originate from vessel walls and may be hypercellular, atypical, pleomorphic or epithelioid
  • Vascular component is in the form of thick walled hyalinized vessels
  • Fat component is in the form of mature adipose tissue and is seen in > 90% of tumors
  • Epithelioid variant (Mod Pathol 2013;26:1355):
    • Pure or predominant population of polygonal cells with clear or densely eosinophilic cytoplasm, large hyperchromatic bizarre nuclei
    • Multilobated nuclei and multinucleation is common
    • Hemorrhage, mitotic figures and necrosis are common
  • Angiomyolipoma with epithelial cysts (AMLEC) represents a morphologic spectrum of the tumors that is characterized by cysts lined by cuboidal or hobnail epithelial cells reminiscent of renal tubular epithelium
Microscopic (histologic) images

Contributed by Tatjana Antic, M.D. and Ankur R. Sangoi, M.D. (Case #359)
Classic variant


Epithelioid angiomyolipoma


Cystic angiomyolipoma

Epithelial cysts (AMLEC)

Sclerosed angiomyolipoma (PEComa)






Cytology description
Positive stains
Negative stains
Electron microscopy description
  • Premelanosomes
Molecular / cytogenetics description
Sample pathology report
  • Right kidney, mass, partial nephrectomy:
    • Angiomyolipoma, classic variant, measuring 3.5 cm in greatest dimension (see comment)
    • Surgical margins, negative for tumor
    • Comment: The sections show well circumscribed tumor composed of adipose tissue, thick walled blood vessels and smooth muscle. There are vessel walls with prominent sclerosis. Immunohistochemical stain SMA is diffusely positive in the vessel walls and the smooth muscle component. HMB45 is focally staining adipose tissue and smooth muscle.
Differential diagnosis
Board review style question #1

    A 16 year old girl with history of seizures was found to have bilateral renal masses containing a fat component on the CT imaging study. Histology is shown in the image above. Which hereditary disease is this patient likely to have?

  1. Birt-Hogg-Dubé
  2. Familiar papillary renal cell carcinoma
  3. Hereditary leiomyomatosis
  4. Tuberous sclerosis
  5. von Hippel-Lindau
Board review style answer #1
D. Tuberous sclerosis. This H&E image of an angiomyolipoma, together with the clinical history of seizures in a young female, is consistent with tuberous sclerosis.

Comment Here

Reference: Angiomyolipoma
Board review style question #2

    A renal tumor from a 43 year old woman shows proliferation of epithelioid cells with abundant eosinophilic cytoplasm and prominent nuclear atypia. What is the best initial immunohistochemical panel for this case?

  1. Cytokeratin, PAX8, CAIX, CD10, vimentin
  2. Cytokeratin, PAX8, CK7, CK20, p53
  3. Cytokeratin, PAX8, MDM2, MyoD1, desmin
  4. Cytokeratin, PAX8, MITF, S100, tyrosinase
  5. Cytokeratin, PAX8, SMA, HMB45, inhibin
Board review style answer #2
E. Cytokeratin, PAX8, SMA, HMB45, inhibin. Differential diagnosis includes high grade renal cell carcinoma, epithelioid angiomyolipoma and metastatic tumors such as melanoma and adrenal cortical carcinoma. Although the panel including cytokeratin and PAX8 could provide a diagnosis of renal cell carcinoma and any panel including HMB45 should be helpful in diagnosing melanoma, the only panel that can help with a diagnosis of epithelioid angiomyolipoma is one that includes SMA.

Comment Here

Reference: Angiomyolipoma
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