Angiomyolipoma – AML
An angiomyolipoma (AML) is the most common benign kidney growth. It has 3 components:
- abnormal blood vessels,
- smooth muscle,
- and fat cells.
While typically benign, the main risk is the potential for the blood vessels to dilate and rupture, leading to serious, life-threatening internal bleeding (hemorrhage).
Symptoms
Most angiomyolipomas are asymptomatic, and the tumors are often discovered incidentally during imaging for other conditions. However, if the tumor grows large or bleeds, symptoms may include:
- Pain or discomfort in the abdomen, back, or side (flank pain).
- A palpable mass in the abdomen.
- Blood in the urine (hematuria).
- Nausea and vomiting.
- High blood pressure (hypertension).
- Anemia (due to chronic blood loss or acute hemorrhage).
Acute, severe pain, sometimes with signs of shock, can indicate a spontaneous rupture and is a medical emergency.
Causes and Risk Factors
The exact cause of sporadic AMLs is not known, but they are linked to genetic mutations.
- Sporadic cases: Account for 80% of cases, typically affecting women over 40 with a single tumor.
- Associated with genetic syndromes: The remaining cases are often linked to genetic disorders like
- Tuberous sclerosis complex (TSC). In TSC patients, AMLs tend to be multiple, bilateral (in both kidneys), larger, and present at a younger age.
- Lymphangioleiomyomatosis (LAM).
Diagnosis
Diagnosis primarily relies on imaging studies, as the fat content in the tumor gives a characteristic appearance.
- Computed Tomography (CT) scans are the standard diagnostic tool for identifying the fat component.
- Magnetic Resonance Imaging (MRI) is useful for cases where CT results are inconclusive, particularly in detecting fat-poor lesions.
- Ultrasound can be used for initial screening or monitoring, but its findings can sometimes overlap with other kidney conditions.
- Biopsy may be necessary if imaging cannot definitively differentiate the mass from a potentially malignant tumor, such as renal cell carcinoma.
Treatment and Management
Management depends on the patient’s symptoms, the tumor’s size and growth rate, and the risk of hemorrhage.
- Active Surveillance: For small (<4 cm) and asymptomatic AMLs, routine monitoring with imaging is generally recommended.
- Embolization: This minimally invasive procedure seals off the blood vessels in the tumor to prevent or treat bleeding. It is a first-line treatment for acute hemorrhage or for preventing rupture in high-risk cases (e.g., aneurysms >5 mm).
- Surgery: Nephron-sparing surgery (partial nephrectomy) is often the preferred surgical option to remove the tumor while preserving kidney function.
- mTOR Inhibitors: Medications like everolimus (Afinitor) are approved for treating TSC-associated AMLs (typically >3 cm) and can shrink the tumors and their associated aneurysms, reducing the risk of bleeding.
Dr Jo Schoeman, Urologist
Suite 46, Level 4
The Wesley Medical Centre
Wesley Hospital
Auchenflower Brisbane
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