American Urological Association - Renal Angiomyolipoma
- Benign tumor composed of fat, smooth muscle cells and thick-walled vessels; believe to originate from perivascular epithelioid cells (PEC) (aka, PEComa).
- Related to other PEComas such as lymphangioleiomyomatosis, "sugar" tumor of lung, cardiac rhabdomyomas, etc.
- May arise in association with tuberous sclerosis:
- >50% of patients with TS develop AMLs; <50% of AML has TS.
- Tend to be asymptomatic, bilateral, small, and multiple.
- Associated with genetic alteration in TSC1 (chr 9q34) and TSC2 (chr 16p13.3).
- Abundant fat containing tumor recognizable radiologically.
- Range from 1-20 cm (average 9 cm).
- Golden-yellow appearance is common, but depends on the ratio (>fat looks like lipoma; > smooth muscle looks like leiomyoma) (image A).
- Usually well-demarcated but not encapsulated.
- May show local "invasion" or extension into perinephric or sinus fat.
- Consists of varying amounts of smooth muscle cells, mature fat and thick-walled vessels
(image B) and (image C).
- Vessels abnormal, often hyalinized and thick with eccentric lumen.
- Smooth muscle cells appear to originate and "radiate" off the vessels (image D).
- AML with benign epithelial cysts (AMLEC) is a rare variant.
- IHC: spindle cells reactive with melanoma marker (HMB-45+, Mart1+) and actin+ thereby distinguishing it from other spindle cell lesions of the kidney.
- DDX: lipoma (for fat predominant AML), leiomyoma (for smooth muscle predominant AML).
- Benign course.
- Surgical intervention recommended for tumors >4 cm (retroperitoneal hemorrhage is common complication).