Angiomyolipoma pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2] Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [3], Faizan Sheraz, M.D. [4], Rekha, M.D.

On gross pathology, well circumscribed and uniform yellow mass is characteristic finding of angiomyolipoma. The components of an angiomyolipoma include vascular cells, immature smooth muscle cells and fat cells. Angiomyolipoma is caused by a defect in TSC1 gene. Diseases associated with angiomyolipoma include von Hippel-Lindau syndrome and tuberous sclerosis. Cytologic features of angiomyolipoma include round nuclei and bland chromatin. Immunohistochemistry markers of angiomyolipoma include positive melanocytic markers.

• Angiomyolipoma is a tumor of the kidney which is composed of three different cells. The cells of angiomyolipoma include the following:
  • Smooth muscle like cells
  • Adipocyte like cells
  • Epithelioid cells
• The cells composing angiomyolipoma are pericytes originated not endothelial.^[1]

• Angiomyolipoma can be a sporadic mutation or part of tuberous sclerosis syndrome.
• There are different variants of angiomyolipoma that are differentiated by biopsy. These variants include:^[2]
  • Classic variant
  • Epithelioid variant
  • Cystic variant which is characterized by solid and cystic regions.

Genes involved in the pathogenesis of angiomyolipoma include:^[3][4]

• TSC1 gene

• TSC2 gene

Conditions associated with angiomyolipoma include:^[5][6][7][8]

• von Hippel-Lindau syndrome
• Tuberous sclerosis

On gross pathology, well circumscribed and uniform yellow mass are characteristic findings of angiomyolipoma.

On microscopic histopathological analysis the following are characteristic findings of angiomyolipoma:^[10]

• Smooth muscles
• Adipose tissue
• Abundant blood vessels

• 
  Histopathologic slide of renal angiomyolipoma. Nephrectomy specimen. H & E stain.^[11]
• 
  Histopathologic slide of renal angiomyolipoma. Nephrectomy specimen. H & E stain.^[11]
• 
  Histopathologic slide of renal angiomyolipoma. Nephrectomy specimen. H & E stain.^[11]
• 
  Histopathologic image of renal angiomyolipoma. Nephrectomy specimen. HMB-45 immunostain.^[11]

Epithelioid angiomyolipoma

• There is a special variant called an epithelioid angiomyolipoma, composed of epithelial looking cells, often with nuclear atypia

Cytologic features of angiomyolipoma include:^[10]

• Nuclei – round/ovoid
• Chromatin – bland

Immunohistochemistry markers of angiomyolipoma include:

• Melanocytic markers positive^[12][13][14]
  • HMB-45 positive in all cases (15/15)^[15]
  • Melan A positive in ~87% of cases (13/15)
• Epithelial markers negative^[12]
  • EMA
  • AE1/AE3
• SMA positive
• CD117 positive/negative
• Ki-67:^[16]
  • Epithelioid variant of angiomyolipoma positive
  • Conventional angiomyolipoma negative

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