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Angiomyolipoma of Kidney

Last updated May 15, 2018

Approved by: Krish Tangella MD, MBA, FCAP


Microscopic pathology image showing angiomyolipoma.

What are the other Names for this Condition? (Also known as/Synonyms)

  • AML of Kidney
  • Kidney AML
  • Renal Angiomyolipoma

What is Angiomyolipoma of Kidney? (Definition/Background Information)

  • An angiomyolipoma (AML) is a benign tumor that is a mixture of blood vessels (angio-), smooth muscles (myo-), and fat (or lipoma). The tumor is seen among a wide age range of adults and can occur at various locations in the body. But, the most common location is the kidney
  • Angiomyolipoma of Kidney (or Renal Angiomyolipoma) is stated to be among the most common benign tumor of the kidney. The tumor may be present in the cortex or medulla of the kidney
  • The kidney consists of 2 zones; the cortex and the medulla. The cortex is the peripheral or outer portion of the kidney, and the medulla is the central or inner portion of the kidney
  • Angiomyolipoma of Kidney can be associated with a syndrome (tuberous sclerosis) in some cases, called syndromic Angiomyolipoma of Kidney; or in a majority of cases, it may not be associated with a genetic disorder, called non-syndromic Angiomyolipoma of Kidney
  • A small proportion of Angiomyolipoma of Kidney cases occur in association with tuberous sclerosis (TS), which is a rare genetic disorder. However, many tumors are sporadic in nature and are often seen in middle-aged adults
  • Many angiomyolipomas are found incidentally while examining the individual for other medical conditions. The signs and symptoms depend upon the size of the tumors and it may include blood in urine, abdominal pain, and frequent infections affecting the urinary tract system. Large tumors are even known to cause chronic kidney failure
  • Typically, a surgical excision of Angiomyolipoma of Kidney with its entire removal is the treatment of choice. Recently, newer therapy involving FDA-approved medications may also be considered
  • The prognosis of Angiomyolipoma of Kidney is excellent with its complete removal, since it is a benign tumor. However, the prognosis also depends upon a set of factors that includes the severity of the signs and symptoms, age and overall health of the individual, response to treatment, and its association with tuberous sclerosis

Who gets Angiomyolipoma of Kidney? (Age and Sex Distribution)

  • The sporadic (non-syndromic) cases of Angiomyolipoma of Kidney are usually seen in the age group 35-50 years
  • When in association with tuberous sclerosis complex (syndromic cases), the age group in which the tumor is often manifested is 20-40 years
  • In rare cases, AML is observed in children too (mostly syndromic type)
  • According to some studies, sporadic cases have a predilection for females. No gender preferences are noted when the tumor is associated with tuberous sclerosis
  • No ethnic or racial preference is seen
  • Among biopsied renal tumors, studies show that AML constitute about 1% of them

What are the Risk Factors for Angiomyolipoma of Kidney? (Predisposing Factors)

Currently, no risk factors have been noted for the sporadic cases of Renal Angiomyolipomas. The sporadic cases are greater in number (around 80-90%) than cases associated with tuberous sclerosis (around 10-20%).

The risk factors for Angiomyolipoma of Kidney may include the following:

  • Tuberous sclerosis (TS) is a risk factor for Renal Angiomyolipoma, and hence, a family history of TS can increase the risk. Tuberous sclerosis complex is an inherited genetic disorder that can cause the formation of other tumor types, such as astrocytomas, rhabdomyomas, phakomas, oncocytomas, and angiofibromas, at various body locations
  • In general, AML can also be associated with other syndromes/disorders including:
    • von Recklinghausen disease (neurofibromatosis type I)
    • von Hippel-Lindau disease
    • Sturge-Weber syndrome
    • Autosomal dominant polycystic kidney disease
  • Some reports indicate that events causing an hormonal imbalance in the body, such as puberty and pregnancy in women, may be a risk factor

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Angiomyolipoma of Kidney? (Etiology)

The exact cause and mechanism of Angiomyolipoma of Kidney formation, in a majority of cases, is unknown. Solitary tumors are believed to be the result of sporadic mutations on TSC1/TSC2 genes, implying that they do not have a preceding family history of the condition.

  • Research has shown that the tumors arise from cells called perivascular epithelioid cells (PEC), which surrounds the blood vessels. Hence, angiomyolipoma (AML) is a type of a tumor known as a PEComa
  • Multiple angiomyolipomas are known to occur in a background of tuberous sclerosis (TS), which is a genetic condition. It may also occur when there is a positive family history of the condition
  • Tuberous sclerosis complex is caused by genetic alterations involving the TSC1 and TSC2 gene. In non-TS associated AML, the loss of heterozygosity on TSC1/TSC2 gene has been noted. Also, some reports indicate that mutations on RHEB gene are observed in sporadic (non-syndromic) cases
  • Some researchers believe that very small nodules with angiomyolipoma-like features occurring in the kidneys may be precursor lesions to AML. In many cases of Renal Angiomyolipoma, such small precursor lesions have been detected in the surrounding kidney tissue to the tumor. Recent studies have shown that such intraglomerular precursor nodules can be seen in both sporadic cases and in Renal Angiomyolipoma associated with tuberous sclerosis. Further, such precursor nodules have also been noted in TSC2/PKD1 contiguous gene syndrome
  • In general, syndromic AML is also associated with other genetic disorders such as von Recklinghausen disease, von Hippel-Lindau disease, Sturge-Weber syndrome, and autosomal dominant polycystic kidney disease
  • Some research indicates that hormonal influence may play a role in AML formation for the following reasons:
    • The tumor is more often seen in women
    • It grows larger during pregnancy
    • The onset can be after puberty
    • And high progesterone receptor activity is present on microscopic examination
  • Lymphangioleiomyomatosis (LAM) and AML association: LAM is a lung condition that occurs in tuberous sclerosis. It is most frequently occurs in girls and young adult women. Studies have shown that LAM and AML of Kidney may be related to each other, since they have overlapping molecular and histological features

What are the Signs and Symptoms of Angiomyolipoma of Kidney?

The signs and symptoms of Angiomyolipoma of Kidney depend on the size and location of the tumor. It can also vary from one individual to another. In general, small tumors are asymptomatic and large tumors (size greater than 4 cm) can cause signs and symptoms.

The signs and symptoms of Angiomyolipoma of Kidney may include the following:

  • The angiomyolipoma can affect the cortex (peripheral portion) or medulla (central portion) of the kidney
  • They can also be present next to the kidney in the soft tissues of the retroperitoneum, with or without any connection to the kidney. In such cases, the tumor is known as retroperitoneal angiomyolipoma and not Renal Angiomyolipoma
  • The kidney symptoms may be caused by retroperitoneal angiomyolipoma due to mass effect (bulky tumors)
  • The tumor may be present as an abdominal mass. It is often well-defined and demarcated
  • It may be associated with frequent urinary tract infections, blood in urine, increased blood pressure, and flank pain
  • Large tumors can severely affect the functioning of the kidney that is involved. Tumors growing to larger sizes can cause compression of adjoining organs and structures, but are not known infiltrate into them
  • Tumors tend to grow larger in size during pregnancy
  • In sporadic cases (when not associated with tuberous sclerosis), angiomyolipoma is usually single. Often with sporadic tumors, they tend to be larger and so pain may be observed
  • In a background of tuberous sclerosis, multiple tumors affecting both the kidneys may be seen. But with TS, tumors are known to be more asymptomatic and often discovered incidentally

The signs and symptoms of the underlying tuberous sclerosis disorder may include the presence of multiple tumors in several parts/organs of the body. Based on the body organ affected (excluding the kidney), the following signs and symptoms of tuberous sclerosis may be noted:

  • Brain - intellectual impairment, behavioral issues, learning difficulties, etc.
  • Heart - affecting blood circulation
  • Eye - white retinal patches
  • Skin - abnormal skin patches, reddish spots on the face
  • Lungs - cystic lesions in the lung due to lymphangioleiomyomatosis

How is Angiomyolipoma of Kidney Diagnosed?

It is important to note that a majority of tumors are sporadic, while a minority of the cases is associated with a syndrome (tuberous sclerosis). The diagnosis of Angiomyolipoma of Kidney may involve the following tests and procedures:

  • Complete physical exam with evaluation of medical history: If angiomyolipoma is associated with tuberous sclerosis; then, the signs and symptoms of tuberous sclerosis may be noted. This can also help the healthcare provider to suspect the condition
  • Plain X-ray of the abdomen
  • CT or CAT scan with contrast of the abdomen usually shows a well-defined mass. This radiological procedure creates detailed 3-dimensional images of structures inside the body
  • MRI scans of the abdomen: Magnetic resonance imaging (MRI) uses a magnetic field to create high-quality pictures of certain parts of the body, such as tissues, muscles, nerves, and bones. These high-quality pictures may reveal the presence of the tumor
  • Ultrasound scan of the abdomen
  • Urine analysis to check for the presence of blood cells
  • Kidney function test
  • Intravenous pyelogram (IVP): A dye is injected into the blood vessels and the image of kidney structure is obtained
  • Vascular angiographic studies of the tumor

Note: CT, MRI scans of the affected kidney can usually help diagnose angiomyolipoma in the kidneys. An ultrasound imaging or CT scan studies can reveal the presence of the tumor due to its high-fat content pattern.

Invasive diagnostic procedures such as:

  • Laparoscopy: A special device is inserted through a small hole into the abdomen, to visually examine it. If necessary, a tissue sample is obtained for further analysis. Exploration of the abdomen using a laparoscope is called ‘exploratory laparoscopy’
  • Laparotomy: The abdomen is opened through an incision for examination, and if required, a biopsy sample obtained. Exploration of the abdomen using laparotomy procedure is called ‘exploratory laparotomy’

Although the above modalities can be used to make an initial diagnosis, a tissue biopsy of the tumor is necessary to make a definitive diagnosis to begin treatment. The tissue for diagnosis can be procured in multiple different ways which include: 

  • Fine needle aspiration (FNA) biopsy of the kidney tumor: A FNA biopsy may not be helpful, because one may not be able to visualize the different morphological areas of the tumor. Hence, a FNA biopsy as a diagnostic tool has certain limitations, and an open surgical biopsy is preferred
  • Core biopsy of the kidney tumor
  • Open biopsy of the kidney tumor

Tissue biopsy:

  • A tissue biopsy of the tumor is performed and sent to a laboratory for a pathological examination. A pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis. Examination of the biopsy under a microscope by a pathologist is considered to be gold standard in arriving at a conclusive diagnosis
  • Biopsy specimens are studied initially using Hematoxylin and Eosin staining. The pathologist then decides on additional studies depending on the clinical situation
  • The tumors may have varying proportions of blood vessels, smooth muscle, and fat cells, when examined by a pathologist under a microscope
  • Sometimes, the pathologist may perform special studies, which may include immunohistochemical stains, molecular testing, and very rarely, electron microscopic studies to assist in the diagnosis

A differential diagnosis, to eliminate other tumor types is considered, before arriving at a conclusion.

  • When an angiomyolipoma occurs in the kidney, the possibility of a renal carcinoma should be ruled out
  • Renal Angiomyolipoma is also known to occur with kidney cancer and oncocytoma (a benign/malignant tumor) affecting the same kidney. Hence, finding a Renal Angiomyolipoma should prompt a closer examination of the rest of the kidney to detect undiagnosed small-sized kidney cancers. This can be performed using detailed imaging studies
  • If the proportion of smooth muscles are more in a Renal Angiomyolipoma, then a leiomyoma should be ruled out

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Angiomyolipoma of Kidney?

The complications of Angiomyolipoma of Kidney may include:

  • Large tumor masses may get secondarily infected with bacteria or fungus
  • Stress and anxiety due to a concern of kidney cancer
  • If bleeding occurs in the tumor suddenly, it can cause retroperitoneal hemorrhage, which can result in large blood loss leading to severe shock. This is a potentially life-threatening complication requiring emergency care. In this situation, the signs and symptoms could be nausea, vomiting, back pain, sudden drop in blood pressure, and palpitations. This clinical condition is termed Wunderlich syndrome
  • The presence of kidney cysts and more than one AML tumors in kidney can cause kidney failure, due to compression of the kidney tissue
  • Chronic renal failure affecting kidney function, if tumors are large; especially when the condition is bilateral (affecting both kidneys)
  • Renal Angiomyolipoma can invade into the renal vein. But, this is only a growth of the tumor and not a sign of malignancy or metastasis
  • Damage to the muscles, vital nerves, and blood vessels, during surgery
  • Post-surgical infection at the wound site is a potential complication
  • Research has not conclusively proven that angiomyolipoma can turn malignant. Although, some cases of sarcoma developing from AML (not associated with tuberous sclerosis) have been noted

How is Angiomyolipoma of Kidney Treated?

The treatment options vary from one individual to another. The treatment measures for Angiomyolipoma of Kidney may include the following:

  • Majority of asymptomatic tumors are not surgically removed: The healthcare provider may recommend a ‘wait and watch’ approach for small-sized tumors presenting mild signs and symptoms, after a diagnosis of angiomyolipoma is made
  • Surgical intervention with complete excision can result in a complete cure. It can also help reduce the chances of tumor recurrence

The surgical treatment methods for Kidney Angiomyolipomas may include:

  • Endoscopic surgery
  • Nephron-sparing surgery
  • Partial or complete nephrectomy
  • Tumor embolization is a possible treatment option. Here the blood supply to the tumor is blocked resulting in its shrinkage or death

A partial or complete nephrectomy may be considered, when large-sized tumors are noted in the kidneys. In severe cases of bilateral tumors, kidney transplantation may be necessary.

  • Newer medical treatments; recently FDA-approved medications may also be used
  • A kidney dialysis may be required, if the kidney function is severely compromised due to renal failure
  • Prompt diagnosis and emergency treatment of any abdominal (retroperitoneal) bleeding due to the tumor should be immediately considered
  • Treatment of the underlying or associated conditions, if any
  • Post-operative care is important: A minimum activity level is ensured, until the surgical wound heals
  • Follow-up care with regular screening may be recommended by the healthcare provider

How can Angiomyolipoma of Kidney be Prevented?

Current medical research has not established a method of preventing both syndromic and non-syndromic forms of Angiomyolipoma of Kidney. However, in case it is associated with genetic disorders, such as tuberous sclerosis, then the following may be considered:

  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as tuberous sclerosis
  • Regular medical screening at periodic intervals with tests and physical examinations are strongly recommended

What is the Prognosis of Angiomyolipoma of Kidney? (Outcomes/Resolutions)

  • The prognosis of Angiomyolipoma of Kidney depends upon the severity of the signs and symptoms. It also depends upon the overall health of the individual, association with tuberous sclerosis, and response to therapy
  • Typically, individuals with small-sized tumors have a better prognosis than those with larger-sized tumors (greater than 4 cm in size). Also, those with non-syndromic (sporadic) tumors have a comparatively better prognosis than individuals with tumors that are seen in association with a genetic disorder (syndromic)
  • In most cases, the prognosis of small-sized solitary tumors is excellent with surgical intervention or appropriate treatment, since these are benign tumors
  • Complications are seen in some cases leading to severely affected kidney function, even causing fatalities. This can occur from hemorrhage of tumor into the retroperitoneal space - mostly with tumors larger than 4 cm. Individuals with retroperitoneal hemorrhage may have a worse prognosis, if the condition is not treated immediately as a medical emergency
  • In pregnant women, such hemorrhage from AML tumors can be significantly serious affecting both the mother and child

Additional and Relevant Useful Information for Angiomyolipoma of Kidney:

Angiomyolipoma can occur at various locations in the body, such as the soft tissue, uterus, fallopian tube, spermatic cord, penis, liver, and lung.

What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Nov. 15, 2016
Last updated: May 15, 2018