Angiomyolipoma is a type of noncancerous kidney tumor consisting of fat, muscle, and blood vessels. It can cause pain and other complications. In some cases, a doctor may remove it.

Angiomyolipomas do not typically cause symptoms and may not require treatment. However, in some cases, they may cause flank pain, blood in the urine, urinary tract infection (UTI), or kidney failure. Rarely an angiomyolipoma can result in a life threatening hemorrhage.

Doctors might also refer to them as renal angiomyolipomas.

This article looks at angiomyolipoma of the kidney, its diagnosis, treatment, and outlook.

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Angiomyolipoma is a type of kidney tumor that is typically benign. While there are many types, most angiomyolipoma growths consist of abnormal collections of fat, smooth muscle cells, and blood vessels. They are one of the most prevalent benign renal masses.

Angiomyolipomas are typically sporadic, and doctors do not associate them with family history. The prevalence of sporadic cases is thought to be 0.44%.

However, in some cases, they may occur as part of tuberous sclerosis complex (TSC) disease. With this rare genetic condition, numerous benign tumors develop in various parts of the body.

TSC may occur as a result of mutations in specific genes — TSC1 or TSC2 — which typically provide instructions for the production of proteins hamartin and tuberin. These proteins have tumor suppressor functions, which means that they help regulate cell growth and division. Mutations in these genes can lead to the production of angiomyolipomas.

Most people do not have symptoms when their doctor diagnoses them with angiomyolipoma.

If someone has symptoms, it most frequently relates to a spontaneous and potentially life threatening hemorrhage. However, this occurs in less than 15% of cases. The bleeding can lead to shock in around 1 in 3 individuals.

Other potential symptoms include:

  • flank pain
  • blood in the urine
  • anemia
  • UTI
  • a mass or lump that people can feel
  • kidney failure

Doctors typically find angiomyolipomas incidentally when they image the kidneys for other reasons, such as blood in the urine or a suspected kidney stone or obstruction. Angiomyolipomas have a typical appearance and may not require further diagnosis.

However, if a doctor requires further evaluation of the kidney mass, they can use various imaging studies. Doctors may use CT, ultrasound, or MRI scans to evaluate the tumor and distinguish it from other types of kidney tumors.

These can include:

Doctors will look for the presence of fat in the tumor. This is a hallmark feature of angiomyolipoma that does not typically appear in renal cell carcinomas. Although, in around 5% of cases, angiomyolipomas are fat-poor, meaning there is a low level of fat within them.

However, doctors can typically distinguish angiomyolipomas from renal cell carcinoma by checking for calcification, which means looking for deposits of calcium. Angiomyolipomas typically do not show calcification.

Sometimes, doctors use digital subtraction angiography to assess tumors further. This imaging study provides details of the blood vessels and blood flow surrounding the tumor.

Most people with kidney angiomyolipomas do not develop symptoms and may not require treatment.

Some situations where a doctor may recommend treatment are ones in which:

  • they suspect that the tumor is malignant (cancerous)
  • there is spontaneous hemorrhaging that leads to serious symptoms
  • there is a risk of the tumor rupturing, which is where the tumor breaks off and fragments enter the blood
  • other complications of the disease occur
  • a person has a large tumor

In some cases, particularly when the angiomyolipoma causes symptoms, a doctor may suggest the following:

  • Selective renal artery embolization: A minimally invasive procedure that involves inserting a catheter through an artery into the leg and guiding it to the renal arteries. The surgeon then injects particles into the blood vessels around the tumor, blocking its blood flow and reducing its size.
  • Nephron-sparing surgery: This procedure removes the tumor while preserving as much kidney tissue as possible.
  • Complete nephrectomy: This is a type of surgery that removes the entire kidney.
  • Ablation: Some methods include cryoablation and radiofrequency techniques. These procedures involve using extreme cold or heat to destroy tumor tissue.
  • Treatment with mTOR inhibitors: These medications may help individuals with TSC manage their angiomyolipomas.

Pregnant people with tumors larger than 4 centimeters may also be given prophylactic treatment even when they have no symptoms. Prophylactic treatment is treatment that aims to prevent a disease from developing.

In around 8 in 10 cases, angiomyolipomas are isolated tumors that most commonly affect middle-aged females.

The remaining 2 in 10 cases occur in individuals with TSC or lymphangioleiomyomatosis (LAM). Both of these are hereditary (inherited) conditions.

LAM is a lung disease involving the abnormal growth of smooth muscle cells in the lungs and lymphatic system.

In people with TSC and LAM, angiomyolipoma affects all genders equally and often begins at a younger age. Angiomyolipomas are also more likely to be aggressive, multiple, large, and occur in both kidneys.

Some factors that can impact angiomyolipoma rupture, where the tumor breaks and enters the blood, include:

  • aneurysm formation
  • genetic abnormalities, such as having TSC or LAM
  • tumor size
  • pregnancy

The outlook for people with angiomyolipoma is generally good when symptoms do not appear and the tumor size remains small.

In cases where an angiomyolipoma causes a hemorrhage, the outlook is variable. People may require emergency embolization to treat the bleeding.

Angiomyolipomas are benign tumors that can occur in the kidneys. Typically, they cause no symptoms, and doctors find them when imaging the kidneys for other reasons.

However, angiomyolipomas can cause flank pain, UTI, and blood in the urine in some cases. In cases where angiomyolipoma causes symptoms, doctors may suggest treatments to block the blood supply to the tumor or remove it. Treatment may require surgery.

The outlook for someone with an angiomyolipoma is good. However, an angiomyolipoma can cause life threatening hemorrhages in rare cases.