An angiomyolipoma is a benign growth that most often develops in the kidney. These growths do not spread to other parts of the body like malignant tumors. While typically harmless, their presence can sometimes lead to complications depending on their size and characteristics.
What is an Angiomyolipoma?
Angiomyolipomas are unique growths composed of three distinct tissue types: fat (adipose tissue), smooth muscle cells, and abnormal blood vessels. These tumors can grow to various sizes, ranging from a few millimeters to over 20 centimeters in diameter.
Most angiomyolipomas occur sporadically, meaning they appear randomly without a clear inherited cause. These sporadic cases account for approximately 80-90% of all angiomyolipomas and are most commonly observed in middle-aged women. In these instances, the tumor typically affects only one kidney and appears as a single growth.
Another type of angiomyolipoma is linked to Tuberous Sclerosis Complex (TSC), a genetic condition. TSC is an inherited disorder characterized by the development of benign tumors, also known as hamartomas, in various organs throughout the body, including the brain, eyes, heart, lungs, and skin. In individuals with TSC, angiomyolipomas are frequently found, affecting 70-80% of patients. These TSC-associated angiomyolipomas often present at a younger age, are more likely to be multiple, and can affect both kidneys.
The underlying cause in TSC is a mutation in either the TSC1 or TSC2 genes, which normally help regulate cell growth and size. When these genes are mutated, the normal inhibitory control over a cellular pathway called mTOR is disrupted, leading to uncontrolled cell growth and the formation of tumors like angiomyolipomas.
How Angiomyolipomas are Discovered
Many angiomyolipomas are discovered by chance during imaging tests for unrelated health concerns. These growths are often asymptomatic. They might be found during routine ultrasounds, CT scans, or MRI of the abdomen.
Larger angiomyolipomas or those that develop complications can manifest with specific symptoms. A common complaint is flank pain, discomfort in the side or back, just below the ribs. Another symptom is hematuria, referring to the presence of blood in the urine. In some cases, if the tumor is particularly large, a person might feel a mass in their abdomen during a physical examination.
Imaging techniques are key in diagnosing angiomyolipomas because they identify the characteristic fat content within the growth. CT scans and MRIs are effective at detecting this fat, which helps differentiate angiomyolipomas from other kidney tumors. These studies also provide information about the tumor’s size, location, and the presence of abnormal blood vessels, aiding in determining the appropriate management strategy.
Managing Angiomyolipomas
The primary concern with angiomyolipomas is the risk of hemorrhage, or bleeding. This risk is particularly elevated for larger tumors, generally those exceeding 4 centimeters in diameter, or those with numerous abnormal blood vessels and microaneurysms. A hemorrhage can manifest as sudden, severe flank pain, and in serious situations, it can lead to symptoms of shock, requiring urgent medical attention. Beyond bleeding, very large angiomyolipomas can also compress surrounding kidney tissue, potentially impairing kidney function over time.
For small, asymptomatic angiomyolipomas, typically less than 4 centimeters, active surveillance is a common approach. This involves regular imaging follow-ups, often yearly, to monitor the tumor’s size and growth rate. This strategy avoids unnecessary interventions, as the decision to observe is based on the low risk of complications for smaller growths.
When intervention is needed, several strategies are available. Embolization is a minimally invasive procedure often used to manage bleeding or to shrink larger tumors. During this procedure, a catheter is guided into the blood vessels supplying the tumor, and small particles are injected to block the blood flow, effectively starving the growth. This can reduce the risk of future hemorrhage and decrease tumor size.
Surgical removal is another option, especially for very large tumors, those causing persistent symptoms, or when there is uncertainty about the diagnosis. Partial nephrectomy, where only the tumor and a small margin of surrounding healthy tissue are removed, is often preferred to preserve as much kidney function as possible. In rare, complex cases involving extremely large tumors or extensive damage, a total nephrectomy might be considered.
For angiomyolipomas associated with Tuberous Sclerosis Complex, specific medications called mTOR inhibitors, such as everolimus, are often used. These medications work by targeting the overactive cellular pathway responsible for tumor growth in TSC. mTOR inhibitors can effectively reduce the size of angiomyolipomas and prevent their further growth, thereby lowering the risk of complications.
The choice of treatment depends on several factors, including the tumor’s size, whether it is causing symptoms, its growth rate, and if it is associated with Tuberous Sclerosis Complex.