Renal Angiomyolipoma on Ultrasound: What Does It Mean?

A renal angiomyolipoma on ultrasound means the scan showed a kidney lesion that looks like an angiomyolipoma (AML), a benign (non-cancerous) growth made of fat, smooth muscle and blood vessels. Many are small, cause no symptoms and are watched with repeat imaging. Further imaging is often used to confirm the finding.

Cleveland Clinic describes AML as the most common benign kidney tumour, and it is often found by chance during imaging for another reason. Finding one does not mean you have kidney cancer. It does mean the report should be followed up so the team can confirm the finding and agree a plan.

This guide is for adults reading an ultrasound report that mentions a possible or likely AML. It explains common terms and questions. It cannot confirm what your lesion is or decide your follow-up.

Larger AMLs can bleed. An NHS hospital leaflet describes bleeding into the abdomen and pelvis as serious or life-threatening. Cleveland Clinic advises prompt care for abdominal or back pain, blood in the urine, fever, nausea and vomiting, or pain in the upper legs.

Call emergency services or go to an emergency department straight away if you have a known or suspected AML and any of the following:

• Sudden or new pain in the side (flank), back or abdomen.
• Visible blood in the urine.
• Dizziness, feeling faint, confusion or a fast heartbeat.
• Pale skin or fast, shallow breathing.

Ultrasound is often where a kidney lesion is first seen, but it does not always settle what the lesion is. The key feature of a typical AML is fat inside it. The American Urological Association (AUA) kidney mass guideline says that, apart from fat-containing AML, current imaging cannot reliably tell benign from malignant kidney tumours.

For that reason, CT or MRI is commonly used to look for fat and to assess the lesion in more detail. The AUA notes that about 5% of AMLs contain little fat and can be hard to identify on imaging. In rare cases a cancer can also contain fat. Cleveland Clinic adds that a biopsy is sometimes suggested when an AML looks similar to kidney cancer.

If your report says 'likely' or 'possible' AML, ask whether CT or MRI is planned and what it is meant to answer.

Size is one of the main things clinicians consider. Cleveland Clinic says problems usually arise when an AML is larger than about 4 cm, and that the risk of bleeding or rupture rises as it grows. An NHS leaflet from University Hospitals of Leicester says AMLs under 4 cm do not usually cause symptoms, while those over 4 cm are more likely to.

Size is not the only factor. Symptoms, growth over time, the AML type, the number of lesions and plans for pregnancy can all affect advice. Cleveland Clinic notes that AMLs can grow faster during pregnancy, so anyone planning a pregnancy should mention this. It also notes that a less common type, called epithelioid AML, is watched more closely.

Ask for the exact measurement on your report, and whether it was compared with any earlier scans.

For small AMLs that are not causing problems, the usual approach is monitoring rather than treatment. Cleveland Clinic describes yearly imaging for AMLs under 4 cm. The Leicester NHS leaflet describes CT or MRI scans every 6 months to a year. Schedules differ between services and people, so confirm yours with the team.

Many classic AMLs do not grow. When they do, Cleveland Clinic gives an average growth of about 0.19 cm a year. Treatment, such as blocking the blood supply (embolisation), heat or freezing treatment, surgery or medicine, is usually considered when an AML is larger, growing or causing symptoms. Your specialist can explain which options apply to you.

Keep copies of each scan report so measurements can be compared over time. If you move or change services, ask how the earlier images, not just the reports, can be shared, so a new team can compare like with like.

AMLs are more likely in people with tuberous sclerosis complex (TSC), a genetic condition. Cleveland Clinic lists TSC as a risk factor. MedlinePlus notes that kidney tumours are common in TSC and can cause serious kidney problems. Other features of TSC can include skin changes, seizures and growths in the brain, heart or eyes.

Cleveland Clinic also lists lymphangioleiomyomatosis (LAM), neurofibromatosis type 1 and von Hippel-Lindau disease as conditions linked with AML. It says people with these conditions should have regular imaging to find AMLs early. If you have several AMLs, AMLs in both kidneys, or a personal or family history of these conditions, ask whether this needs looking into.

Bring the full ultrasound report and any earlier scan reports. Write the answers next to each question.

• Is the AML confirmed, or does it still need CT or MRI to look for fat?
• What size is it, and has it changed compared with earlier scans?
• Is it a classic AML, or could it be another type that needs closer review?
• How often should I have follow-up imaging, and which type of scan?
• At what size or change would treatment be discussed?
• Does anything in my history suggest tuberous sclerosis or a related condition?
• Which symptoms mean I should seek emergency care?
• Should I mention this AML if I plan a pregnancy or start a new medicine?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a kidney AML described their reports, follow-up schedules and the questions they asked can help you plan your own list before an appointment.

Other people's cases cannot tell you what your lesion is or how it will behave, and we make no promises about outcomes. Use them to prepare questions, not to replace advice from your own team. If your report mentions a kidney cyst instead, see our guide to simple and complex kidney cysts.