Angiomyolipoma

• Benign mesenchymal tumor of kidney
• Rare
• Histopathology
  • No true capsule
  • Commonly bleed
  • Tumor composed of fat, smooth muscle, aggregates of thick-walled blood vessels
    
    
• Types
  
  
  • Isolated angiomyolipoma is most common (80%)
    • Usually solitary
    • Unilateral (80% on right side)
    • Not associated with tuberous sclerosis
    • Mean age of incidence: 40s
    • Much more common in females
  • Angiomyolipoma associated with tuberous sclerosis (in 20%)
    • Angiomyolipoma occurs in 80% of patients with tuberous sclerosis
      • Commonly large
      • Usually bilateral
      • Usually multiple
    • May be only evidence of tuberous sclerosis
    • Mean age of incidence: teens
    • Equal incidence in males and females
      
      
• Signs and symptoms
  
  
  • Small lesions are asymptomatic (60%)
  • Acute flank / abdominal pain (due to hemorrhage) most common presenting symptom
  • Hematuria (40%)
  • Palpable mass (47%)
  • Shock (due to massive retroperitoneal hemorrhage)
    
    
• Imaging findings
  
  
  • Mostly small lesions <5 cm in diameter
  • Many have a large exophytic component (25%)
  • Calcifications not common (6%)
  • Plain film findings
    • Mass of fat lucency is lesion is large enough
  • CT findings
    • Well-marginated, cortical-based, heterogeneous tumor predominantly of fat density (<-20 HU)
    • Variable enhancement (smooth muscle, vessels)

Angiomyolipomas of both kidneys are seen to contain fat

• US findings
  • Highly echogenic tumor due to high fat content
  • Less echogenic areas due to hemorrhage, necrosis, dilated calyces
• MRI findings
  • Intra-tumoral fat seen with fat-suppression technique
  • Variable areas of high signal intensity on T1WI
• Angiographic findings
  • Hypervascular mass (95%)
    • Enlarged interlobar + interlobular feeding arteries
      • Tortuous, irregular, aneurysmal, venous pooling, "sunburst" / "whorled" / "onion peel" appearance, no AV shunting
        
        

• Complications
  
  
  • Angiomyolipomas >4 cm bleed spontaneously in 50-60%
    • Hemorrhagic shock from bleeding into angiomyolipoma or into retroperitoneum
      
      
• Treatment
  
  
  • Annual follow-up of lesions <4 cm
  • Emergency laparotomy is required in some including nephrectomy, tumor resection
  • Selective arterial embolization can be done
    
    
• DDx
  
  
  • Renal / perirenal lipoma or liposarcoma
  • Wilms tumor
  • Renal cell carcinoma which will occasionally contain fat