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Angiomyolipoma
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- Benign tumor composed of fat, muscle and thick-walled vessels; probably more of a hamartoma than a real neoplasm.
- Occurs in two distinct settings:
- In association with Tuberous Sclerosis
- approximately 50% of patients with TS develop angiomyolipomas.
- tend to be asymptomatic, bilateral, small, and multiple.
- strong female predominance.
- Sporadic cases
- tumors tend to symptomatic, unilateral, and large.
- Gross features: range from 1-20 cm (average 9 cm); golden-yellow appearance is common, but depends on the ratio of fat:muscle:vessels; usually well-demarcated but not encapsulated; may show local “invasion”
- Histologic features:
- consists of varying amounts of smooth muscle, fat, and thick-walled vessels.
- smooth muscle often “spins” off of the vessels, creating a “pinwheel” appearance (shown at right).
- may see nuclear pleomorphism, local invasion and vascular invasion, but these features do not affect the prognosis.
- Special stains: smooth muscle fibers are reactive with HMB-45 (usually a melanoma marker), thereby distinguishing it from all other spindle cell lesions of the kidney.
- Differential diagnosis: lipoma, leiomyoma
- Clinical behavior/ treatment: benign; surgical intervention recommended for tumors > 4 cm (hemorrhage is common complication).
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