What is an angiomyolipoma (renal hamartoma)?

From the Guidelines

Angiomyolipoma is a benign tumor composed of blood vessels, smooth muscle cells, and fat cells that most commonly occurs in the kidney, and its treatment depends on size and symptoms, with small, asymptomatic tumors usually monitored with periodic imaging, while larger or symptomatic ones may require procedures like embolization or partial nephrectomy. The vessels within angiomyolipomata are fragile because they lack a complete elastic layer, which can lead to microaneurysms and spontaneous bleeding 1. TSC-associated angiomyolipomata tend to be multiple and bilateral, and in patients with TSC2 pathogenic variants, angiomyolipomata arise at a younger age, are more prone to bleeding complications, and grow faster than in those with sporadic angiomyolipomata 1. Some key characteristics of angiomyolipomata include:

• They usually appear hyperechoic and homogeneous in ultrasound imaging, but these characteristics are not pathognomonic 1
• They can be detected with ultrasound, CT, or MRI, but the choice of imaging modality depends on the patient's body habitus and the need for radiation exposure 1
• The fat content in these tumors gives them a characteristic appearance on imaging studies, making them relatively easy to diagnose without biopsy 1
• Treatment options include embolization, partial nephrectomy, or medical management with mTORC1 inhibitors like everolimus or sirolimus 1
• The main concern with these tumors is the risk of bleeding, which increases with tumor size, and preventive arterial embolization may be considered for asymptomatic angiomyolipoma with a threshold diameter >4 cm 1. Some important considerations in the management of angiomyolipomata include:
• The use of mTORC1 inhibitors like everolimus or sirolimus, which can help reduce tumor size and prevent bleeding complications 1
• The role of interventional radiology, including arterial embolization, in the treatment of bleeding angiomyolipomata or preventive treatment of large asymptomatic tumors 1
• The potential benefits and risks of surgical intervention, including partial nephrectomy, in the treatment of angiomyolipomata 1

From the Research

Definition and Composition of Angiomyolipoma

• Angiomyolipoma (AML) is the most common benign tumor of the kidney, composed of blood vessels, smooth muscle, and fat components in varying proportions 2, 3, 4, 5, 6.
• It is also known as renal hamartoma, a neoplasm of mesenchymal origin 2.

Types and Associations of Angiomyolipoma

• AMLs are divided into two types: sporadic and tuberous sclerosis complex (TSC)-associated 3.
• TSC-associated AML develops at a younger age and tends to exhibit a faster growth rate than sporadic AML 3.
• AMLs can be classified as classic AML, fat-poor AML, and epithelioid AML, with epithelioid AML showing aggressive behavior 3.

Clinical Presentation and Management

• AMLs are often discovered incidentally on imaging, but symptomatic presentation can occur, including spontaneous retroperitoneal hemorrhage or bleeding into the urinary collection system 4, 5, 6.
• The risk of bleeding is related to tumor size and the grade of the vascular component of the tumor, with larger tumors (>4 cm) having a higher risk of bleeding 4, 5.
• Management options include active surveillance, partial nephrectomy, transcatheter arterial embolization, and mammalian target of rapamycin (mTOR) inhibitor treatment, with the choice of treatment depending on the size and symptoms of the tumor 2, 3, 5.