Kidney Angiomyolipoma

Angiomyolipomas are common benign (noncancerous) tumors of the kidney composed of three types of cells: vascular cells, immature smooth muscle cells, and fat cells. These benign tumors are mainly found in the kidney, but they can also be found occasionally in the liver, and rarely in the ovary, Fallopian tube, spermatic cord, palate, and colon.

Older medical literature may refer to angiomyolipomas as hamartomas or choristomas. This article will mainly describe angiomyolipoma as related to the kidneys although very infrequently, angiomyolipomas may occur in other organs.

Most people with angiomyolipomas have no symptoms or signs. However, even though they are considered to be benign tumors, some can cause symptoms and signs in patients if the tumor becomes large and/or if the blood vessels in the angiomyolipoma leak blood (rupture).

In this case, the following symptoms and signs may occur:

• Sudden pain (back pain or flank pain)
• Nausea
• Vomiting
• Anemia
• Hypertension
• Chronic kidney disease
• Shock (about 20% of patients that show symptoms develop shock)

The exact cause of angiomyolipoma is not known. Researchers suggest that the cause of these benign tumors is a mutation in a common progenitor cell (for example, a stem cell that has the potential to develop into any of the three types of cells listed above). Angiomyolipoma tumors are associated with the inherited genetic disease tuberous sclerosis (a rare genetic disease that causes benign tumors to grow in the brain and other organs) and possibly associated with other syndromes like Sturge-Weber syndrome or neurofibromatosis. Animal experiments suggest that a high-fat, low carbohydrate diet may hasten the growth and development of angiomyolipoma tumors in rats, but it's unknown if such a diet will hasten angiomyolipoma tumor development in humans.

The preliminary diagnosis of angiomyolipoma is usually done either incidentally while the patient is undergoing imaging tests for other reasons or directly by ultrasound, CT scan, and/or MRI scan. Urologists, radiologists, and emergency medicine physicians are often the first doctors to suspect and/or diagnose these tumors. In addition, ob-gyn doctors may find such tumors while doing ultrasound studies on pregnant females; angiomyolipoma bleeding problems are rare but possible in pregnancy.

Angiomyolipoma can be treated by the drug everolimus (Afinitor) that works by blocking the human target of rapamycin (mTOR) protein to affect many processes involved in cell growth. Researchers suggest that even if asymptomatic, angiomyolipoma that grows to 3 cm or more in diameter should be treated. Another treatment is embolization (technique in which the blood vessels in an angiomyolipoma tumor are sealed off); this technique can be preventative and is suggested to be used in angiomyolipomas 4 cm in diameter or larger to reduce the risk of hemorrhage (vessel rupture). Patients with angiomyolipoma tumors that are small and asymptomatic should be routinely seen with follow-up visits and measurements of the angiomyolipoma tumor size as some may quickly develop a growth rate of up to about 4 cm per year.

In general, the prognosis of angiomyolipoma is good as long as the tumors don't have dilated blood vessels or grow rapidly. However, the prognosis decreases if the tumor becomes very large or compromises the kidney's function so that it may need to be removed or the patient may require dialysis. In addition, if the patient develops a hemorrhage, the prognosis, if the patient is not diagnosed and quickly treated, is fair to poor.

Although it is not possible to prevent angiomyolipomas from developing, it is possible to reduce the possibility that they can cause serious problems. For example, asymptomatic angiomyolipoma can be treated before they have a chance to come symptomatic, thus preventing angiomyolipoma symptoms and signs.