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- Benign
- Composed of variable amounts of fat, smooth muscle and abnormal blood vessel
- Occur spontaneously
- Women in 50s
- Younger age, multiple in patients with tuberous sclerosis
- Rare in neurofibromatosis and in adult polycystic kidney disease
- Consists of thick-walled inelastic blood vessels
- Risk of hemorrhage higher in lesions larger than 4 cm in diameter
Imaging
- USG
- Depends on proportions of fat, muscle and vascular content, any hemorrhage
- Circumscribed, highly reflective mass, more echogenic than central sinus fat
- 30% renal cell carcinomas <3 cm in diameter are highly reflective
- Posterior shadowing is typical that distinguishes from malignancy
- CT
- Fatty mass with areas of tissue density
- Attenuation of -15 HU is diagnostic
- Perirenal fat being engulfed by a lesion suggests malignancy
- Angiography
- Multiple aneurysms
- ‘onion layer’ appearance
- Embolization helps control bleeding tumors and treat large tumors to reduce risk of bleed