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What is an Angiomyolipoma?

By Emma Lloyd
Updated May 17, 2024
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An angiomyolipoma is a benign fatty tumor that can form in kidneys. They are made up of muscle and vessels as well as fatty tissue. The incidence rate in the general population is about 0.3%, although that figure is much higher when associated with a condition called tuberous sclerosis. Most of these tumors are harmless and are isolated cases that do not recur although, very rarely, one can become cancerous or cause hemorrhaging.

About 80% of angiomyolipomas develop spontaneously in the absence of any other disease. More than half of tumors do not cause any symptoms, with symptoms more likely to occur if the tumor approaches or exceeds 1.6 inches (4 cm) in size. They usually are non-threatening, but larger tumors can cause potentially serious symptoms. For an unknown reason, about 80% form in the right kidney.

Most tumors grow without any underlying cause, but people with a genetic condition called tuberous sclerosis are at increased risk of developing an angiomyolipoma. This rare disease causes tumors to grow in many organs, including the brain, heart, lungs and skin, in addition to the kidneys. Up to 80% of people with tuberous sclerosis develop one or more on the kidneys, which are also called renal angiomyolipomas.

As the fatty tumor grows larger, it can cause abdominal pain, fever, nausea and weight loss. These symptoms are much more likely to occur in people who have tuberous sclerosis, as they generally occur when tumors are very large or when multiple tumors are present. Large tumors are at risk of hemorrhaging, which is potentially life-threatening.

Small, isolated tumors are unlikely to cause symptoms and might remain undiagnosed altogether. They often are diagnosed only when a patient undergoes a medical imaging scan for an unrelated condition. Those that are associated with tuberous sclerosis are more likely to be diagnosed, because people with this condition undergo regular medical imaging tests for screening purposes.

Asymptomatic tumors need not be treated as long as they remain small, but a larger tumor might need to be removed to prevent hemorrhaging. Angiomyolipomas are prone to spontaneous hemorrhage once they reach a certain size because the walls of blood vessels in these tumors are structurally weak. Rarely, a kidney might need to be removed altogether; this usually is carried out only in someone with tuberous sclerosis and when a kidney contains multiple tumors.

An alternative treatment, called transcatheter arterial embolization, might sometimes be carried out in preference to kidney removal. In this procedure, an artery that feeds the kidney is catheterized, and a substance that causes blood vessels to coagulate is fed into the tumor to prevent hemorrhaging. This option is used only when someone with tuberous sclerosis has multiple renal tumors and is not carried out in cases of spontaneous isolated ones.

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Discussion Comments
By anon998908 — On Sep 19, 2017

I have a 7cm tumor on left kidney and may need to have it removed since chance of rupture is high. Now that I'm aware of it, every little ache back there worries me. Hopefully it will be dealt with before anything happens but this article lets me know what to expect if it ever does bleed.

By anon997834 — On Mar 06, 2017

I had my left kidney removed with a grapefruit size angio (zero symptoms, otherwise very healthy), and only found out after it hemorrhaged. You definitely know when you are hemorrhaging. You have pain, nausea, extreme sweating, essentially you feel like you are dying. You are bleeding internally, so you have a very hard, expanding abdomen. It is life-threatening and hopefully you are near a hospital.

By anon995797 — On May 26, 2016

Trust me, you will know when you are hemorrhaging, for you will have pain along the flank, back and legs like you have never experienced before. When you reach the hospital, don't let them waste a lot of time with all sorts of tests. Let them know you have been diagnosed with the cyst so they can get right to it.

By anon991975 — On Aug 02, 2015

I was just wondering if anyone has hemmorraged and if so, what does that mean? How do you catch it? How do you know you're hemmorraging? What are the symptoms? I'm a little afraid of not making it to the hospital.

By anon963919 — On Aug 01, 2014

It is important and easy to understand what is an angiomyolipoma of the kidney. Very good information and learning. Thank you.

By anon942450 — On Mar 27, 2014

I drove myself to the er with severe back, flank pain. A ct showed a 11cm tumor on the right adrenal gland and lots of bleeding. Renal embolization to was performed to stop the bleeding. This article gives me a clear idea of what has happened and what will happen with these forms of lipomas. Thanks for the info.

By anon352339 — On Oct 22, 2013

I was diagnosed with angiomyolipoma in September and was advised to either have embolization or removal surgery. Can anybody tell me which treatment is better, safer and has the fewest complications, please?

By anon313189 — On Jan 10, 2013

I lost my right kidney due to angios, also had a pheochromocytoma, a tumor in the adrenal gland, which caused a heart attack due to an adrenaline surge. They removed my adrenal gland. Now I have angios in my left kidney and was told by the neurologist today the two together very very uncommon. I will be having genetic testing in the near future.

By anon309183 — On Dec 15, 2012

This is a good article. I had a angiomyolipoma removed from my left kidney three years ago. It was very painful prior to surgery. The tumor was on the vena cava so it was a challenge for the surgeon to remove it without taking the whole kidney. Recently, I have the symptoms back in full force and suspect a recurrence of the tumor.

By anon283269 — On Aug 03, 2012

I just had my right kidney removed due to this type of tumor, 9cm with no symptoms and discovered by accident. This article was very helpful in understanding what it was.

By anon223696 — On Oct 20, 2011

Thank you for a clear and comprehensive article. I just read the results of my scan and your article has prepared me well for my next visit to the urologist.

By anon201217 — On Jul 29, 2011

Thank you! I was just diagnosed, and this is the first article that I feel truly explains what this is in an easy to understand manner.

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