Renal angiomyolipoma (AML) is a non-cancerous (benign) renal tumour that is found in the kidneys and made up of fat cells, blood vessels and muscle cells.¹ Understanding renal AML is crucial as it helps individuals recognise their condition, its associated risks, and the available treatment options. This knowledge helps patients make informed decisions about their health and seek timely medical advice and intervention when necessary.

Read on to learn more about the causes, diagnosis, and treatment options for renal AML.  

Causes and risk factors

Renal AMLs often occur sporadically, in about 80% of cases, meaning that they happen by chance and are not inherited.¹ It is not known exactly why these sporadic cases occur, but it may result from spontaneous genetic mutations. Renal AMLs occur more commonly in people assigned female at birth (AFAB) than in those assigned male at birth (AMAB), which has been linked to oestrogenic effects.¹ Additionally, these tumours are often found to be larger in people AFAB  than in those AMAB, which could also be due to hormonal effects which contribute to the growth of the tumour.¹

The other 20% of cases may be associated with hereditary conditions, such as tuberous sclerosis and pulmonary lymphangioleiomyomatosis. Tuberous sclerosis is a rare, inherited, genetic disorder that causes benign tumours to form in many areas of the body, including the brain, eyes, lungs, and kidneys.² Pulmonary lymphangioleiomyomatosis is another rare genetic disease which typically affects people AFAB of childbearing age. This disease can cause angiomyolipomas to develop in the kidneys.³

Hereditary angiomyolipomas are more likely to be bigger, grow faster, begin at an earlier age, and cause chronic renal failure compared to sporadic angiomyolipomas.⁴ Hereditary renal AMLs are caused by mutations in genes which code for essential proteins.⁴ If these proteins cannot be produced, due to genetic mutations, it will result in uncontrolled activation of the mTOR pathway.⁵ The mTOR pathway can be thought of as a series of signals which are responsible for telling cells to grow. When the mTOR pathway is overactive, cells receive too many signals and begin to grow uncontrollably.⁵ This can lead to the growth of tumours such as renal AMLs.

Symptoms and diagnosis

Renal AML can be quite challenging to diagnose, due to its tendency to stay asymptomatic.⁶ As it commonly develops without causing any noticeable signs, individuals may not realise they have renal AML. This makes routine health check-ups and screenings pivotal for early detection. Despite its often asymptomatic nature, renal AML can sometimes exhibit symptoms. These may include:⁶

• Abdominal or flank pain: Individuals with renal AML may experience pain in the abdomen or flank (area below the ribs). This discomfort may range from mild to severe and could be irregular or persistent.
• Haematuria (blood in the urine): The presence of blood in the urine can signify various conditions and it is one of the symptoms associated with renal AML. Blood in the urine may be visible to the naked eye or can be detected through urine tests.
• Palpable abdominal mass: In some cases, individuals may feel a lump or mass in the abdomen upon physical examination, either during routine medical checks or self-examination.

Detecting renal AML involves a combination of medical examinations and tests:⁶

• Diagnostic imaging tests: Imaging techniques, such as CT scans, MRI scans and ultrasonography can be used to examine the kidneys in detail and identify lesions.
  • Ultrasonography can detect a renal mass but is not reliable for an initial diagnosis, therefore CT scans are used to detect and diagnose renal tumours.
• If the CT scan is unclear due to the renal mass containing fewer fat cells, then an MRI scan can be used to identify fat-poor renal AMLs as it is more sensitive.
• For lesions with very low/no fat cell content, imaging studies will not work for diagnosis and a biopsy will be required.
• Biopsy: Occasionally, biopsies may be recommended to differentiate malignant tumours from benign renal AMLs. This procedure involves removing a small sample of tissue from the affected area using a hollow needle and examining it under the microscope.

Treatment options

Addressing renal AML involves diverse options that vary based on the size of the tumour, symptoms, and individual health circumstances. The following criteria should be considered when recommending any medical intervention:^1,7

• Persistent pain caused by the tumour
• Large lesions (>6cm)
• Lesions that are growing in size with observation
• Limited access to emergency care
• Lesions in those AFAB of childbearing age
• Patients AFAB taking hormonal therapy

For small renal AMLs that are asymptomatic, observation may be recommended instead of medical intervention. This approach involves regular monitoring through diagnostic imaging tests and check-ups.⁷ The purpose of this approach is to track any changes in the tumour’s size or the onset of symptoms. Possible interventions for individuals with renal AMLs include treatment with mTOR inhibitors, embolisation and surgical excision.

mTOR inhibitors:⁸ As mentioned previously, hereditary renal AMLs are caused by mutations in genes which result in uncontrolled activation of the mTOR pathway, leading to the growth of tumours. Certain drugs target the mTOR pathway, known as mTOR inhibitors. These drugs stop the activation of the mTOR pathway and can interrupt tumour growth by stopping cell growth signals. Sirolimus and Everolimus are mTOR inhibitors that have been approved by the US Food and Drug Administration for treating hereditary renal AMLs. Although these drugs can successfully be used to treat renal AML, they are not without their side effects which include but are not limited to:

• Amenorrhoea (absence of menstrual periods)
• Fatigue
• Hyperglycaemia (elevated blood glucose levels)
• Delayed wound healing
• Infections

Embolisation:⁹ Embolisation involves blocking the blood vessels that supply the renal AML by introducing material into the blood vessels, leading to their blockage. This is followed by shrinkage of the tumour as it is no longer able to receive a blood supply of oxygen and nutrients which it needs to grow. Again, embolisation is not without its risks and can lead to several side effects such as:

• Flank pain
• Fever
• Vomiting
• Nausea

Surgical excision:⁹ Partial or complete nephrectomy involves surgical removal of part of the kidney or the removal of the entire kidney. For smaller renal AMLs or cases where preserving the kidney function is crucial, partial nephrectomy can be used to remove the tumour while sparing the healthy part of the kidney. In more severe cases of renal AML, a complete nephrectomy may be necessary to remove the entire kidney. Nephrectomy is usually recommended when there is a high risk of progression to malignancy, or the renal tumour is large.

Individuals must consult with healthcare professionals to determine the most suitable treatment plan. Each approach for treatment has its considerations and risks, and the choice of treatment is typically tailored to the specific situation of the patient.

Prognosis and follow-up

The prognosis or outlook for individuals diagnosed with renal AML is generally favourable, especially for small asymptomatic tumours. These small AMLs often have a low likelihood of causing significant problems.¹⁰ However, the prognosis can vary based on factors such as tumour size, symptoms, and individual health conditions. Larger or symptomatic AMLs may have a different prognosis and could require more proactive management to prevent progression to more serious health conditions.¹⁰

Regular follow-up and monitoring are crucial for patients diagnosed with renal AML. Even if the tumour is small and causing no symptoms, routine check-ups and imaging tests are essential to track any changes in the tumour size or the emergence of symptoms. These regular check-ins help healthcare providers decide if and when intervention might be necessary. Early detection and intervention can significantly impact the management and prognosis of AML, making consistent follow-up a vital part of care.

Summary

Understanding Renal Angiomyolipoma (AML) is essential for individuals concerned about their kidney health. This non-cancerous tumour, made up of fat cells, blood vessels, and muscle cells, often goes unnoticed as it typically shows no symptoms. Regular health check-ups play a crucial role in catching AML early, ensuring timely intervention and effective management. The causes of AML, whether sporadic or associated with conditions like Tuberous Sclerosis and Pulmonary Lymphangioleiomyomatosis highlight the importance of recognising risk factors and genetic influences in kidney health.

Diagnosing AML involves various tests and imaging techniques, allowing healthcare providers to distinguish between benign and harmful growths in the kidneys. The available treatments range from observation for smaller, asymptomatic AMLs to more targeted interventions, such as mTOR inhibitors, embolisation, or surgical procedures, for larger or symptomatic tumours. Though small, asymptomatic AMLs generally show a positive prognosis, regular check-ups and monitoring remain important. These routine appointments help healthcare professionals track any changes and ensure quick action if the tumour shows signs of growth or symptoms emerge. Individualised care plans, guided by informed decisions and close medical attention, greatly influence the successful management of AML. Early detection, supported by consistent monitoring, remains fundamental for effective management and more favourable outcomes for individuals diagnosed with Renal Angiomyolipoma. This awareness empowers individuals to take charge of their kidney health and collaborate closely with healthcare providers to ensure the best possible care.