Radiology · Renal Angiomyolipoma

Understanding Your Diagnosis: Renal AML and PEComa

At a Glance

Most renal angiomyolipomas (AMLs) are benign kidney tumors made of blood vessels, smooth muscle, and fat, and many need only regular imaging. Fat-poor or epithelioid types and signs of tuberous sclerosis complex may require additional testing or closer follow-up.

Receiving a diagnosis that includes the word “tumor” often triggers an immediate sense of panic. However, for the vast majority of people diagnosed with a renal angiomyolipoma (AML), the situation is much less dire than the word suggests ^[1]. When confirmed by imaging or biopsy, these growths are usually benign (non-cancerous) and are often discovered entirely by accident during imaging tests for unrelated issues, such as a gallbladder check or a routine physical ^[2].

What is a PEComa?

An AML is the most common member of a family of tumors known as PEComas (perivascular epithelioid cell tumors) ^[3]. A “classic” AML is composed of three distinct types of tissue, which give the tumor its name:

Angio-: Blood vessels that are often thick-walled and slightly malformed ^[4].
Myo-: Smooth muscle tissue or fibers ^[5].
Lipoma: Adipose (fat) tissue ^[6].

The amount of each tissue varies from person to person. Some tumors are “fat-rich” and easy to identify on a CT scan, while others are “fat-poor” and may require more detailed testing to distinguish them from kidney cancer ^[7]^[8].

Sporadic vs. TSC-Associated AML

While many AMLs look similar under a microscope, they generally fall into two categories based on how and why they developed.

Feature	Sporadic AML	TSC-Associated AML
Frequency	About 80% of cases	About 20% of cases
Typical Age	Usually diagnosed in older adults ^[9]	Often diagnosed in children or young adults ^[10]
Number	Typically a single, solitary tumor ^[11]	Often multiple tumors in both kidneys (bilateral) ^[12]
Growth Rate	Generally grows very slowly over years ^[13]	Tends to grow more quickly ^[13]
Cause	Occurs randomly; no clear genetic link	Caused by a genetic condition called Tuberous Sclerosis Complex (TSC) ^[14]

Most people have the “sporadic” version, meaning it happened by chance and is not related to an underlying genetic syndrome. However, if your imaging shows many tumors in both kidneys, or if you have a family history of the disease, your doctor may refer you for genetic counseling to evaluate you for TSC ^[12].

(Note: Small studies show highly variable growth rates. One small cohort estimated sporadic growth around 2.7 mm/year and TSC growth around 5.4 mm/year, while other large series found almost zero growth in sporadic cases ^[13]^[9]. Your individual tumor’s growth can only be known by comparing your own scans over time).

Understanding the “Benign” Label

It is important to understand that “benign” does not mean “invisible.” While classic AMLs do not spread to other parts of the body (metastasize) like cancer does, they are active growths.

Most AMLs are considered “classic” and remain stable for years ^[15]. However, a very rare histologic subtype known as epithelioid AML (which is a diagnosis made by a pathologist under a microscope, not on an imaging scan) can behave more aggressively and requires closer monitoring ^[16].

Because many of these tumors are found when they are small and causing no symptoms, the most common “next step” isn’t surgery, but rather active surveillance—watching the tumor with regular scans to ensure it isn’t growing at a rate that requires intervention ^[17].

Common questions in this guide

What is a renal angiomyolipoma (AML)?

A renal angiomyolipoma is a usually benign growth in the kidney made of blood vessels, smooth muscle, and fat. Many are found by chance during imaging for another reason and cause no symptoms. Most classic AMLs do not spread to other parts of the body.

Does having a renal AML mean I have kidney cancer?

Usually not. Most classic AMLs are benign and do not spread to other parts of the body, although a rare epithelioid AML can behave more aggressively. Imaging, biopsy, or pathology findings help determine the subtype and follow-up needed.

What does PEComa mean in an AML diagnosis?

PEComa stands for perivascular epithelioid cell tumor, a family of tumors that includes renal angiomyolipoma. A classic AML contains varying amounts of thick-walled blood vessels, smooth muscle, and fat. This mixture can make some AMLs easy or difficult to recognize on a CT scan.

How are sporadic and TSC-associated AMLs different?

Sporadic AMLs develop without a known genetic syndrome and are usually a single, slow-growing tumor in an older adult. TSC-associated AMLs are linked to tuberous sclerosis complex and are more often found in younger people as multiple tumors in both kidneys. They may grow more quickly and may prompt genetic evaluation.

Why can a fat-poor AML be hard to diagnose?

A fat-poor AML contains little visible fat, so it may resemble another kidney growth on a CT scan. Additional imaging or a biopsy may be needed to make the diagnosis more certain. Fat-poor does not automatically mean the tumor is cancerous.

Do all renal AMLs need surgery?

No. Small AMLs that cause no symptoms are often managed with active surveillance, using regular scans to check for growth. The decision to observe or intervene depends on factors such as the tumor’s size, location, growth pattern, and subtype.

When should someone with AML be checked for tuberous sclerosis complex?

A clinician may consider evaluation for tuberous sclerosis complex when AMLs are multiple or present in both kidneys, when they appear at a younger age, or when there is a suggestive family history. Genetic counseling can help determine whether testing is appropriate. The pattern on imaging and any other health findings are considered together.

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Curated prompts to bring to your next appointment.

1.What specific subtype of AML do I have: classic, fat-poor, or epithelioid?
2.Are there features on my imaging that suggest I should be screened for Tuberous Sclerosis Complex (TSC)?
3.Based on the size and location of my tumor, what is the current plan for monitoring its growth?
4.Does my pathology or imaging report mention any 'atypical' features that might change how we manage this?
5.If my tumor is 'fat-poor,' how certain are we that this is an AML and not another type of kidney growth?

References (17)

1
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2
Renal Angiomyolipoma: The Good, the Bad, and the Ugly.
Vos N, Oyen R
Journal of the Belgian Society of Radiology 2018; (102(1)):41 doi:10.5334/jbsr.1536.
PMID: 30039053
3
Sustained response to pembrolizumab in recurrent perivascular epithelioid cell tumor with elevated expression of programmed death ligand: a case report.
McBride A, Garcia AJ, Sanders LJ, et al.
Journal of medical case reports 2021; (15(1)):400 doi:10.1186/s13256-021-02997-x.
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4
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Hepatobiliary & pancreatic diseases international : HBPD INT 2016; (15(6)):660-664 doi:10.1016/s1499-3872(16)60077-2.
PMID: 27919857
5
[Hepatic epithelioid angiomyolipoma/PEComa and focal nodular hyperplasia in a patient with a previous history of cutaneous melanoma].
Machado I, Marhuenda A, Trallero M, et al.
Revista espanola de patologia : publicacion oficial de la Sociedad Espanola de Anatomia Patologica y de la Sociedad Espanola de Citologia 2019; (52(4)):250-255 doi:10.1016/j.patol.2018.05.001.
PMID: 31530409
6
PEComa-A Rare Liver Tumor.
Krawczyk M, Ziarkiewicz-Wróblewska B, Wróblewski T, et al.
Journal of clinical medicine 2021; (10(8)) doi:10.3390/jcm10081756.
PMID: 33919494
7
New radiologic classification of renal angiomyolipomas.
Song S, Park BK, Park JJ
European journal of radiology 2016; (85(10)):1835-1842 doi:10.1016/j.ejrad.2016.08.012.
PMID: 27666625
8
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat.
Park BK
AJR. American journal of roentgenology 2017; (209(4)):826-835 doi:10.2214/AJR.17.17973.
PMID: 28726505
9
Natural History of Renal Angiomyolipoma (AML): Most Patients with Large AMLs >4cm Can Be Offered Active Surveillance as an Initial Management Strategy.
Bhatt JR, Richard PO, Kim NS, et al.
European urology 2016; (70(1)):85-90 doi:10.1016/j.eururo.2016.01.048.
PMID: 26873836
10
Renal Manifestations of Tuberous Sclerosis Complex: Key Findings From the Final Analysis of the TOSCA Study Focussing Mainly on Renal Angiomyolipomas.
Kingswood JC, Belousova E, Benedik MP, et al.
Frontiers in neurology 2020; (11()):972 doi:10.3389/fneur.2020.00972.
PMID: 33041968
11
Renal angiomyolipoma in patients with tuberous sclerosis complex: findings from the TuberOus SClerosis registry to increase disease Awareness.
Kingswood JC, Belousova E, Benedik MP, et al.
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12
Late-Onset Diagnosis of Tuberous Sclerosis Complex Revealed by Renal Angiomyolipoma: A Case Report.
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13
Renal angiomyolipoma-patient characteristics and treatment with focus on active surveillance.
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15
Renal angiomyolipoma with tuberous sclerosis complex: How it differs from sporadic angiomyolipoma in both management and care.
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16
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17
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This page provides general information about renal angiomyolipoma and PEComa subtypes for informational purposes only and does not constitute medical advice. Your clinician, radiologist, and pathologist can interpret your specific scans and report.

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