Discrete renal mass with varying amounts of dysmorphic blood vessels, smooth muscle, and mature adipose tissue

Variable size, can be very large

Single or multiple

Classic angiomyolipoma (AML): Lipid-rich echogenic mass with posterior acoustic shadowing

Fat-poor subtype (“AML with minimal fat”): Usually hyperechoic but fat not detected by CT or MR

CT/MR more specific than US

Color Doppler: Absent from fatty component, may be present in soft tissue/vascular components

Renal cell carcinoma

After acute hemorrhage, renal cell carcinoma or AML may be indistinguishable if no fat is detected

Wilms tumor

Renal oncocytoma

Deep cortical scar with fat

Cortical milk of calcium cyst

Can be classified radiologically into “classic” and “fat-poor” subtypes

Most common benign solid renal neoplasm

80% sporadic; prevalence: 0.2%; 4th-6th decades; usually unilateral and solitary; F:M = 3:1

20% associated with tuberous sclerosis complex; mean age: younger; 55-75% of these patients will have AML by 3rd decade; any subtype of AML, multiple and bilateral

Tend to grow faster when > 4 cm

Size > 3-4 cm or aneurysm size > 5 mm → bleeding

Majority detected as incidental finding on imaging and asymptomatic, during screening of tuberous sclerosis

Can present with spontaneous renal hemorrhage, which may obscure mass

Sporadic form more common in females than males

AML associated with tuberous sclerosis complex more likely to need some form of treatment

Echogenic masses detected by US should be further evaluated with CT or MR to confirm presence of fat

US may be used for screening and monitoring of AML, depending on body habitus