Kidney tumor
Benign adult tumors
Epithelioid angiomyolipoma

Topic Completed: 1 January 2012

Revised: 6 November 2019

Copyright: 2003-2019,, Inc.

PubMed Search: Epithelioid angiomyolipoma [title] kidney

Mandolin S. Ziadie, M.D.
Page views in 2018: 3,864
Page views in 2019 to date: 3,833
Cite this page: Ziadie MS. Epithelioid angiomyolipoma. website. Accessed December 6th, 2019.
Definition / general
  • Epithelioid variant of angiomyolipoma (AML), also described as atypical or oncocytoma-like AML
  • An epithelioid component of AML is present in 8% of cases with a mean volume of 51% of tumor (Am J Surg Pathol 2009;33:289)
  • May include cases diagnosed incorrectly as renal cell carcinoma in tuberous sclerosis patients (Am J Surg Pathol 1998;22:180)
Clinical features
  • More likely than typical AML to display aggressive behavior or to undergo malignant transformation, but rarely metastasizes
Case reports
Microscopic (histologic) description
  • Triphasic tumor composed of smooth muscle, adipose tissue and vasculature with a predominance of epithelioid cells ranging from uniform polygonal cells with mild atypia to bizarre multinucleated straplike cells and epithelioid giant cells
  • Thin or thick hyaline cords may represent sclerosed vessels; often no recognizable fat, may lack characteristic vascularity
  • Nuclear atypia (93%), often mitotic figures (47%), coagulative tumor necrosis (27%) or hemorrhage
  • Features of concern for possible transformation include: nuclear anaplasia, atypical mitoses and geographic necrosis
  • Tuberous sclerosis related cases are more likely to have microscopic AML foci, epithelioid component and epithelial cysts (Am J Surg Pathol 2009;33:289)
Microscopic (histologic) images

Contributed by Dr. Anuradha Ananthamurthy

Various images


CK (negative)

EMA (negative)


Case of the Week #32






Smooth muscle actin

Images hosted on other servers:

Various images

Well circumscribed solid tumor

44 year old woman with atypical epithelioid cells
1: nonencapsulated but well demarcated tumor; Fig 2: epithelioid cells with abundant clear to lightly
eosinophilic granular cytoplasm, large pleomorphicvesicular nuclei and prominent eosinophilic nucleoli;
3: huge straplike cells with eosinophilic cytoplasm, multiple peripheral nuclei; Fig 4: HMB45+

Cytology description
  • Large, atypical cells with abundant, round to polyhedral, granular cytoplasm
  • Occasional intranuclear cytoplasmic inclusions, occasional bizarre, giant nuclei with hyperchromasia and huge nucleoli and occasional mitotic figures (Acta Cytol 2002;46:545)
Cytology images

AFIP images

Smooth muscle and adipose tissue

Negative stains
Differential diagnosis
  • Adrenocortical carcinoma: usually different location, often huge, may have normal adrenal gland component; negative for melanocytic markers
  • Melanoma: marked atypia, no prominent adipose or vascular component
  • Oncocytoma: no prominent adipose or vascular component, negative for melanocytic markers
  • Renal cell carcinoma: usually marked atypia and infiltrative margins, not triphasic; negative for melanocytic markers
  • Primary renal sarcoma: usually no prominent epithelioid component, negative for melanocytic markers
  • Sarcomatoid renal cell carcinoma: has residual renal cell carcinoma component, negative for melanocytic markers
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