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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors

Epithelioid angiomyolipoma

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 27 January 2012, last major update January 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● 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)

Clincal features

● More likely than typical AML to display aggressive behavior or to undergo malignant transformation, but rarely metastasizes

Case reports

● 28 year old man with malignant transformation (Am J Surg Pathol 2002;26:523)
● 44 year old woman (Arch Pathol Lab Med 2004;128:1176)
● 47 year old man with microhematuria (Arch Pathol Lab Med 2004;128:e19)
● 50 year old woman with lung and abdominal metastases (Am J Surg Pathol 2000;24:889)
● 73 year old woman with kidney tumor initially called renal cell carcinoma (Hum Pathol 2000;31:516)
● Malignant tumor arising in association with classic AML (Am J Surg Pathol 2001;25:121)
● Two patients (Arch Pathol Lab Med 2002;126:610)
● Two fatal cases (Arch Pathol Lab Med 1994;118:735)

Micro 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)

Micro images


Various images

Whole mount shows well-circumscribed solid tumor with no adipose tissue or thick walled vessels

44 year old woman with atypical epithelioid cells - Figure 1: non-encapsulated but well demarcated tumor; fig 2: epithelioid cells with abundant clear to lightly eosinophilic granular cytoplasm, large pleomorphic vesicular nuclei and prominent eosinophilic nucleoli; fig 3: huge straplike cells with eosinophilic cytoplasm, multiple peripheral nuclei; fig 4: HMB45+

Virtual slides

Epithelioid angiomyolipoma

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

Smooth muscle and adipose tissue

Positive stains

● HMB45, NCI-C3
● Ki-67 (Int Urol Nephrol 2009;41:559)

Negative stains

● AE1-AE3, CAM5.2, EMA, S100 and desmin

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

Additional references

Am J Surg Pathol 1997;21:1123, Am J Surg Pathol 1998;22:663

End of Kidney tumor - cysts, children, adult benign > Benign (usually) adult tumors > Epithelioid angiomyolipoma

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