An angiomyolipoma is a type of non-cancerous tumor that most commonly develops in the kidneys. These benign growths do not spread to other parts of the body. While primarily found in the kidneys, angiomyolipomas can occasionally appear in other organs such as the liver, or more rarely, in locations like the ovary, fallopian tube, or colon.
Characteristics of Angiomyolipoma
Angiomyolipomas are composed of a mixture of three tissue types: abnormal blood vessels, smooth muscle cells, and fat cells. This specific composition distinguishes them from other kidney growths. These tumors are benign and do not become cancerous.
The size of an angiomyolipoma can vary significantly, ranging from a few millimeters to over 20 centimeters. Smaller tumors often remain unnoticed and cause no significant issues. Larger angiomyolipomas can lead to symptoms, especially if the abnormal blood vessels within them rupture and bleed. The fragile nature of these blood vessels increases the risk of complications as the tumor grows.
How Angiomyolipoma is Detected
Many angiomyolipomas are discovered incidentally during imaging scans for unrelated medical conditions, as they often cause no symptoms. When symptoms do occur, they may include pain in the flank or back, blood in the urine (hematuria), or a palpable abdominal mass. A sudden rupture of the tumor’s blood vessels can lead to severe abdominal pain and a drop in blood pressure.
Diagnostic imaging techniques are essential for identifying angiomyolipomas. Ultrasound is often the initial method, showing brighter areas due to fat content. Computed tomography (CT) scans provide detailed images and effectively confirm the presence of fat within the tumor, a key diagnostic feature. Magnetic resonance imaging (MRI) offers excellent soft tissue detail, useful for distinguishing angiomyolipomas from other kidney masses, even those with low fat content. These imaging studies usually provide enough information for diagnosis, making a biopsy rarely necessary.
Causes and Associated Conditions
The exact reason angiomyolipomas develop is not always known; many cases occur sporadically without a clear cause or family history. These sporadic angiomyolipomas are more common, accounting for 80% to 90% of cases, and are frequently observed in middle-aged women. The remaining cases are linked to a specific genetic disorder.
Angiomyolipomas are strongly associated with Tuberous Sclerosis Complex (TSC), a rare inherited genetic condition. TSC causes benign tumors to grow in various organs throughout the body, including the brain, kidneys, heart, lungs, and skin. Individuals with TSC often develop multiple angiomyolipomas, which can affect both kidneys and tend to be larger than those that occur sporadically. However, not everyone with an angiomyolipoma has TSC.
Treatment Approaches
Not all angiomyolipomas require active treatment, particularly if they are small and do not cause any symptoms. For these cases, “watchful waiting” is often recommended, involving regular monitoring with imaging tests to track the tumor’s size and characteristics. This approach is typically chosen for tumors smaller than 4 centimeters.
Intervention becomes necessary for larger tumors, those causing symptoms, or those at high risk of bleeding. One common treatment is embolization, a procedure that blocks the blood supply to the tumor, causing it to shrink and reducing the risk of hemorrhage. Surgical options include nephron-sparing surgery, also known as partial nephrectomy, which removes the tumor while preserving as much healthy kidney tissue as possible. If the tumor is very large or problematic, a total nephrectomy, the removal of the entire kidney, may be considered. For angiomyolipomas associated with Tuberous Sclerosis Complex, specific medications called mTOR inhibitors, such as everolimus, can be used to reduce tumor size and manage their growth.