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renal epithelioid angiomyolipoma

Friday 23 April 2010

renal epithelioid angiomyolipoma with atypia; Epithelioid variant of angiomyolipoma (AML), atypical or oncocytoma-like AML

PO

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