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

• Metanephroid Renal Tumor
• Nephroblastoma-like Adenoma of Kidney
• Renal Metanephric Adenoma

What is Metanephric Adenoma of Kidney? (Definition/Background Information)

• Metanephric Adenoma of Kidney is a rare benign tumor consisting of epithelial cells. It arises from the distal nephron or collecting ducts of the kidney. The tumor is seen in a wide age range of individuals
• 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. The tumor may be present in the cortex or medulla of the kidney
• Many Metanephric Adenoma of Kidney tumors 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 can potentially cause chronic kidney failure
• Typically, a surgical excision of Metanephric Adenoma of Kidney with its entire removal is the treatment of choice. The prognosis is excellent with its complete removal, since it is usually a benign tumor. However, the prognosis also depends upon a set of factors that includes the severity of the signs and symptoms and one’s response to treatment

Who gets Metanephric Adenoma of Kidney? (Age and Sex Distribution)

• The Metanephric Adenoma of Kidney are usually seen in the age group of 5 to 83 years. The average age of presentation is 41 years
• Even though both males and females are affected, a predilection for females is noted. The female-male ratio is 2:1
• No specific ethnic or racial preference is seen

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

• Currently, no definitive risk factors have been noted for Metanephric Adenoma of Kidney

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's 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 Metanephric Adenoma of Kidney? (Etiology)

The exact cause and mechanism of Metanephric Adenoma of Kidney formation, in a majority of cases, is unknown. Research has shown that the tumors arise from cells of distal nephron or collecting ducts from the metanephric blastema.

• Studies have shown that Metanephric Adenoma of Kidney exhibits certain genetic mutations. These mutations may help in the diagnosis of the tumor
• Some of the mutations detected include:
  • Chromosomal deletion 2p
  • BRAF gene mutations
  • Genetic mutations at 2p13

Metanephric Adenoma of Kidney tumors do not have gains in chromosome 7, gains in chromosome 17, and loss in chromosome 4. This helps distinguish the tumor from papillary renal cell carcinoma (a type of kidney cancer).

What are the Signs and Symptoms of Metanephric Adenoma of Kidney?

The signs and symptoms of Metanephric Adenoma 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 can cause signs and symptoms. The kidney symptoms may be caused due to mass effect (presence of bulky tumors).

The signs and symptoms of Metanephric Adenoma of Kidney may include the following:

• The tumor may be present as an abdominal mass
• It is often well-defined and demarcated
• The tumors can range in size from 0.3 cm to 15 cm
• 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.
• 12% of the tumors are known to be associated with polycythemia (paraneoplastic syndrome)

How is Metanephric Adenoma of Kidney Diagnosed?

In many cases, Metanephric Adenoma of Kidney is diagnosed incidentally during imaging studies undertaken for some other health conditions. The diagnosis may involve the following tests and procedures:

• Complete physical exam with evaluation of medical history
• Complete blood counts with hematocrit (to detect polycythemia)
• Plain X-ray of the abdomen
• CT or CAT scan with contrast of the abdomen may show 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

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
• 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.

The differential diagnosis includes:

• Metastatic insular thyroid carcinoma
• Papillary renal cell carcinoma
• Wilms tumor

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 for Metanephric Adenoma of Kidney?

The complications of Metanephric Adenoma of Kidney may include:

• 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, this signs and symptoms could be nausea, vomiting, back pain, sudden drop in blood pressure, and palpitations. This clinical condition is termed Wunderlich syndrome
• Chronic renal failure affecting kidney function if tumors are large, is a potentially complication
• The tumors can be multifocal and affect both the kidneys
• 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 Metanephric Adenoma of Kidney can turn malignant. 

How is Metanephric Adenoma of Kidney Treated?

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

• Majority of asymptomatic tumors are not surgically removed after the tumor is determined to be benign on a biopsy: The healthcare provider may recommend a ‘wait and watch’ approach for small-sized tumors presenting mild signs and symptoms, after a diagnosis of Metanephric Adenoma of Kidney is made, through a fine needle aspiration or a core biopsy.
• 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 Metanephric Adenoma of Kidney 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. 

• 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
• Postoperative 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 Metanephric Adenoma of Kidney be Prevented?

• Current medical research has not established a method of preventing Metanephric Adenoma of Kidney
• Regular medical screening at periodic intervals with tests and physical examinations are strongly recommended

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

The prognosis of Metanephric Adenoma of Kidney depends upon the severity of the signs and symptoms. It also depends upon the overall health of the individual and response to therapy.

• Typically, individuals with small-sized tumors have a better prognosis than those with larger-sized tumors
• In most cases, the prognosis of small-sized solitary tumors is excellent with surgical intervention or appropriate treatment, since these are benign
• 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

Additional and Relevant Useful Information for Metanephric Adenoma of Kidney:

Please visit our Cancer & Benign Tumors Health Center for more physician-approved health information:

http://www.dovemed.com/diseases-conditions/cancer/