Description, Causes and Risk Factors:
Angiomyolipoma is the most common benign tumor of the kidney. It is composed of fat, smooth muscle, and abnormal blood vessels. The prevalence M:F is 0.02:0.29.
Angiomyolipomas are rare lesions, often arising in the kidney and are a part of a group of tumors with a diverse appearance known as PEComas (tumors of perivascular epithelioid cell origin). Angiomyolipoma most commonly occurs in the kidney. The next common site is the liver. Extrarenal angiomyolipomas are extremely rare and have been reported in the liver, colon, suprasellar region, small intestine, skin, intranodal, omentum, breast and adrenal gland. Adrenal angiomyolipoma is extremely rare and only three cases have been reported so far.
One case was reported in the setting of tuberous sclerosis and other two were sporadic. The previous sporadic case was 8 cm in size in a 46-year-old female. Both previously reported cases were in the left adrenal gland. The case in the setting of tuberous sclerosis was very small while the sporadic one was larger i.e., 8 cm.
Angiomyolipomas predominately composed of smooth muscle cells are known diagnostic challenges to pathologists. They are often misdiagnosed as sarcomatoid carcinoma, carcinoma or sarcoma. Some of these tumors have malignant potential and recur locally. A diligent search for adipocytes and abnormal blood vessels may help in confirming the diagnosis.
Small angiomyolipomas and those without dilated blood vessels (aneurysms) cause few problems, but angiomyolipomas have been known to grow as rapidly as 4 cm in one year. An angiomyolipoma larger than 5 cm and those containing an aneurysm pose a significant risk of rupture, which is a medical emergency as it is potentially life threatening. One population study found the cumulative risk of hemorrhage to be 10% in males and 20% in females. A second problem occurs when the renal angiomyolipomas take over so much kidney that the function is impaired leading to chronic kidney disease. This may be severe enough to require dialysis. A population survey of patients with TSC and normal intelligence found 1% were on dialysis.
Symptoms may include:
Acute/chronic abdominal pain.
- Acute/chronic flank pain.
- Nausea and vomiting.
- Palpable abdominal mass.
- Palpable flank mass.
- Microscopic hematuria.
- Gross hematuria.
- Urinary tract infection (UTI).
- Renal failure.
In the evaluation of angiomyolipoma, one of the most important roles of the radiologist may be to differentiate it from renal cell carcinoma (RCC) because the treatment strategies for the two disease entities are quite different: Asymptomatic angiomyolipoma is not an indication for surgery, whereas RCC should be completely removed. Although typical angiomyolipoma can easily be diagnosed with various imaging studies, angiomyolipoma with minimal fat may mimic RCC in various imaging studies, leading to unnecessary surgery.
There are three methods of scanning that detect angiomyolipoma: ultrasound, CT and MRI. Ultrasound is standard and is particularly sensitive to the fat in angiomyolipoma but less so to the solid components. However it is hard to make accurate measurements with ultrasound. Computed tomography (CT) is very detailed and fast and allows accurate measurement. However, it exposes the patient to radiation and the dangers that a contrast dye used to aid the scanning may itself harm the kidneys. Magnetic resonance imaging (MRI) is safer than CT but many patients (particularly those with the learning difficulties or behavioral problems found in tuberous sclerosis) require sedation or general anesthesia and the scan cannot be performed quickly.Some other kidney tumors contain fat, so the presence of fat is not diagnostic. It can be difficult to distinguish a fat-poor angiomyolipoma from a renal cell carcinomaand a lesion growing at greater than 5 mm per year may warrant a biopsy in order to distinguish it from a from this form of cancer.
The 2 mainstays of treatment for angiomyolipoma are surgery and renal angioembolization (RAE). Other management strategies include surveillance, total nephrectomy and investigational medical management, such as hormonal therapy or use of mammalian target of rapamycin (mTOR) inhibitiors, such as sirolimus. The optimal modality of treatment is still unclear. There are no prospective or randomized studies comparing RAE and surgery, and no treatment guidelines. Instead, urologists must consider several factors including treatment efficacy and morbidity, patient renal function, individual tumor characteristics, operative time and patient/surgeon preference.
Large angiomyolipomas even if asymptomatic should be removed to avoid complications like spontaneous rupture owing to the presence of abnormal elastin and poor vascularity in the tumor. Nevertheless, follow-up is necessary because of atypical morphology.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.