renal epithelioid angiomyolipoma

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Epithelioid cellular morphology can be seen in clinically benign usual angiomyolipomas (AMLs).

Epithelioid AMLs can be divided into those without and with atypia, the latter category associated in the literature with malignant potential.

This model accurately categorized 78% of clinically malignant and 100% of the clinically benign epithelioid AMLs with atypia. (20410812)

An epithelioid component is present in 8% of cases of AML with a mean volume of 51% of tumor (Am J Surg Pathol 2009;33:289).

Microscopy

 Triphasic tumor associating smooth muscle, adipose tissue and vessels
 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;
 no recognizable fat,
 may lack characteristic vascularity
 Nuclear atypia (93%),
 often mitotic figures (47%),
 coagulative tumor necrosis (27%)
 hemorrhage
 possible transformation include:

• nuclear anaplasia
• atypical mitoses
• geographic necrosis

Predisposition

 tuberous sclerosis

• Tuberous sclerosis related cases are more likely to have microscopic AML foci, epithelioid component and epithelial cysts (Am J Surg Pathol 2009;33:289).

Immunochemistry

 HMB45+
 melan-A+

Cytology

 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)

Differential diagnosis

 Renal cell carcinoma

• Many cases are diagnosed incorrectly as renal cell carcinoma in tuberous sclerosis patients (Am J Surg Pathol 1998;22:180)
• usually marked atypia and infiltrative margins, not triphasic;
• negative for melanocytic markers

 Primary renal sarcoma

• usually no prominent epithelioid component, negative for melanocytic markers

 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

 Sarcomatoid renal cell carcinoma

• has residual renal cell carcinoma component,
• negative for melanocytic markers

See also

  renal angiomyolipoma

Prognosis

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

References

 Renal Epithelioid Angiomyolipoma With Atypia: A Series of 40 Cases With Emphasis on Clinicopathologic Prognostic Indicators of Malignancy. Brimo F, Robinson B, Guo C, Zhou M, Latour M, Epstein JI. Am J Surg Pathol. 2010 Apr 20. PMID: 20410812