What is Angiomyolipoma (AML), a benign renal tumor?

From the Guidelines

Angiomyolipoma is a benign tumor that requires no treatment if it is small (less than 4 cm) and asymptomatic, but for larger tumors (greater than 4 cm) or those causing symptoms, treatment options include selective arterial embolization or surgical removal through partial nephrectomy, with mTOR inhibitors like everolimus being a viable option for patients with tuberous sclerosis complex. The management of angiomyolipoma should prioritize minimizing the risk of spontaneous bleeding and preserving kidney function, as highlighted in a study published in Nature Reviews Nephrology 1. Key considerations in the management of angiomyolipoma include:

• Tumor size and growth rate: Regular monitoring with ultrasound or CT scans is recommended, with frequency depending on size and growth rate 1.
• Symptoms: Pain, bleeding, or other symptoms may necessitate intervention, such as selective arterial embolization or surgical removal 1.
• Patient characteristics: Patients with tuberous sclerosis complex may benefit from treatment with mTOR inhibitors like everolimus to reduce tumor size and minimize the risk of bleeding 1.
• Pregnancy: Closer monitoring is recommended during pregnancy due to the increased risk of growth and bleeding in women with angiomyolipomas 1. The use of mTOR inhibitors like everolimus has been shown to be effective in reducing tumor size and minimizing the risk of bleeding, with a recommended starting dose of 10 mg daily for adults and 4.5 mg/m2/day for children 1. However, the decision to initiate treatment should be individualized, taking into account the patient's specific characteristics, tumor size, and growth rate, as well as the potential risks and benefits of treatment, as emphasized in a study published in Nature Reviews Nephrology 1.

From the Research

Definition and Classification of Angiomyolipoma

• Angiomyolipoma (AML) is the most common benign tumor of the kidney, consisting of blood vessels, smooth muscle, and fat components in varying proportions 2.
• AML is divided into the sporadic type and tuberous sclerosis complex (TSC)-associated type, with TSC-associated AML developing at a younger age and exhibiting a faster growth rate than sporadic AML 2.
• AMLs are classified as classic AML, fat-poor AML, and epithelioid AML, with epithelioid AML being rare and showing aggressive behavior leading to distant metastasis and mortality 2.

Management and Treatment of Angiomyolipoma

• Active surveillance is the suggested management for small AML, while clinical intervention is mainly indicated when there is a substantial risk of rupture 2.
• Minimally invasive therapies, including partial nephrectomy, transcatheter arterial embolization, and mammalian target of rapamycin (mTOR) inhibitor treatment, are employed for patients who require treatment 2.
• Treatment intervention is recommended for TSC-associated AML >3 cm, even in asymptomatic cases, and for asymptomatic sporadic AML >4 cm in size or with an intra-tumoral aneurysm of >5 mm 2.
• Selective arterial embolization (SAE) is effective in controlling hemorrhage from AMLs in the acute setting, but has a significant complication rate and limited value in long-term management 3.

Risk Factors and Complications of Angiomyolipoma

• Larger tumor size, younger patient age, and higher BMI value are correlated with a higher risk of tumor hemorrhage 4.
• The optimal cut-off point for predicting SAML tumor hemorrhage is 7.35 cm, and tumor sizes less than 7.35 cm can be managed with active surveillance or TAE for hemorrhage prevention 4.
• The major complication of AML is intra-tumoral or retroperitoneal hemorrhage due to rupture, which can be serious and life-threatening 2.

Natural History and Growth of Angiomyolipoma

• The natural history of AML can be divided into two distinct groups based on tumor size, with tumors less than 4 cm being less likely to be symptomatic and requiring surgery 5.
• Documented growth of AML during the study period was observed in 27% of tumors less than 4 cm and 46% of tumors greater than 4 cm 5.
• Patients with TSC and AML tend to present at a younger age, have a higher incidence of bilateral renal involvement, and are more symptomatic, with larger tumors that are more likely to grow and require surgery 5.