What are the Different Types of Kidney Mass?

Erin J. Hill

There are many different types of kidney masses, ranging from cysts to adenomas to fibromas. All of them can be categorized as benign, which means non-cancerous, pre-cancerous, which means that it may eventually cause cancer, and malignant, or cancerous. The majority of small kidney growths are benign, while larger ones are more likely to be cancerous. Most masses are diagnosed incidentally, as they often don't cause symptoms. If treatment is required, there are a variety of options, including watching and waiting, medication, and surgery.

An example of a healthy kidney and one with tumors, a type of kidney mass.
An example of a healthy kidney and one with tumors, a type of kidney mass.

Symptoms and Diagnosis

Many kidney masses don't cause any symptoms at all, and may be discovered incidentally through an X-ray, Computed Tomography (CT) scan, Magnetic Resonance Imaging (MRI) study, or an ultrasound that's being done for another procedure. Those that do cause symptoms may cause unexplained fatigue, blood in the urine, back pain near the ribs, stomach pain, and unexplained weight loss. If a kidney mass is particularly large, a person may be able to feel it through his or her skin. Sometimes pain in other parts of the body can be a sign of renal cancer specifically, especially if it is in the advanced stages and had spread beyond the kidneys. Since kidney stones cause many of these symptoms as well, masses are sometimes mistaken for them, but they can generally be distinguished by the symptoms, since they also cause a fever and a burning sensation while urinating, as well as much more pain.

An example of a healthy kidney and one with polycystic kidney disease, which causes many small masses called cysts.
An example of a healthy kidney and one with polycystic kidney disease, which causes many small masses called cysts.

Once a growth is suspected, healthcare professions generally recommend a person to a urology clinic for testing. While there, the person generally gives a urine sample and a blood sample, and may have his or her urethra and bladder examined in a procedure called a cytoscopy. Clinicians may also do additional MRIs or ultrasounds to learn more about the mass, particularly its size, as this can help them determine whether it's likely to be cancerous or not. A mass of about 1.5 in (4 cm) or less is only about 20 to 30% likely to be cancerous, while those larger than 2.75 in (7 cm) are about 90% likely to be cancerous. Healthcare providers may also take a biopsy, which is a small sample of the mass, to find out more about it. Once they know what the growth is and how large it is, they can recommend a course of treatment.

Urine samples will help to diagnose kidney masses.
Urine samples will help to diagnose kidney masses.


Many growths are actually cysts, which are fluid-filled sacs in or on the kidney. Cysts are almost always benign, though if they grow large enough, they may have to be removed. Most of the time, they don't affect the function of they kidney though, and can be left in place. One exception of this is in those with Polycystic Kidney Disease (PKD), in which a person has multiple renal cysts. This can cause high blood pressure, anemia, liver problems, and long-term damage to the kidneys. It requires ongoing treatment with diuretics and blood pressure medication, as surgery is generally not effective.

A renal ultrasound may be conducted to confirm the presence of a kidney mass.
A renal ultrasound may be conducted to confirm the presence of a kidney mass.

Renal Adenoma

Renal adenoma is the most common type of benign kidney mass, and generally presents as small growths. These tumors are mostly asymptomatic, and their cause is unclear. Sometimes they are classified as precancerous, and they are virtually always closely monitored for growth. Many doctors choose to surgically remove renal adenomas to prevent the possibility of them becoming cancerous in the future.

Surgery may be required to remove a large angiomyolipoma to prevent hemorrhaging.
Surgery may be required to remove a large angiomyolipoma to prevent hemorrhaging.

Renal Onocytoma

Another relatively common kidney mass is renal onocytoma, a tumor that can grow very large and often affects other organs. In its initial stages it may not cause any symptoms, and is most likely to show up during another procedure or when it grows large enough to press on other organs. It's not entirely clear what causes it, but it is known that those with the genetic condition Birt–Hogg–Dubé syndrome, are more likely to get it, and that men are more likely to get it than women are. A renal onocytoma is also considered precancerous and is most often surgically removed before it can develop into cancer.


Angiomyolipoma is a very rare type of kidney mass that usually comes as a side effect of a genetic mutation. A condition known as tuberous sclerosis often accompanies angiomyolipomas. Patients who do not experience any symptoms related to the tumors are usually watched closely for any changes, but they typically don’t receive any treatment unless symptoms appear.

Fibromas and Lipomas

Fibromas and lipomas are two very rare types of benign kidney growths, which are often not distinguishable from cancerous growths. It's entirely known what causes fibromas or lipomas, but lipomas are thought to have a genetic link. They may eventually develop into cancer, and can then metastasize, or spread, throughout the patient’s body. For this reason, they are generally removed via surgery.


The two most common types of kidney cancer are renal cell carcinoma and urothelial cell carcinoma. It's not entirely clear what causes them, but known risk factors include smoking, obesity, hypertension, hepatitis C, and long-term exposure to hazardous chemicals. Treating kidney cancer can be difficult, since it does not always respond well to chemotherapy or radiation. Surgery is generally recommended if the tumor hasn't spread, but if a patient isn't a good candidate for surgery because of already having had one kidney removed or other health issues, radiofrequency ablation or cryotherapy may also be used. The first is the use of a high frequency electrical current to remove cancerous cells, and the second involves freezing them.

Wilms' Tumor

Wilms’ tumor is a rare type of kidney cancer that is most common in those under 5. Children who develop it generally have a good outlook, as it is often curable. The symptoms and diagnosis method for this type of tumor are generally the same as those for other renal masses. In most cases, the tumor is removed, and in some cases the entire kidney is taken out to prevent the spread of the cancer.

A mass does not necessarily indicate the presence of kidney cancer.
A mass does not necessarily indicate the presence of kidney cancer.

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Discussion Comments


To the author, do some research and correct your article. "A mass of about 1.5 in (4 cm) or less is only about 20 to 30% likely to be cancerous" is simply untrue and grossly inaccurate. In fact, it is closer to the other extreme ... masses 4cm or less are 20% to 30% likely to be benign.


I am 73 years old and had an adrenal tumor so large they removed the kidney. They called it renal cell carcinoma. That was nine years ago. Now they have found a spot on my one remaining kidney which they call a mass, because it is not a cyst, but it is very tiny. I also have a 1.9 cm cyst (Bosniak) on that kidney. I am being sent to a surgeon.

I have had many other surgeries on my abdomen and wonder if it is wise to have another surgery with only this one kidney. Every time you have abdominal surgery you risk blockage from scar tissue in your intestines. I've been there. Last year, I had five feet of my intestines removed from just that. I have heard different beliefs that radiation actually will help the kidney, so I am in a quandary as to what to do. Suggestions or experiences would be welcome.


My 63 year old sister (who has been a heavy smoker for over 30 years) found out she has a mass on her kidney. They say since the mass is bigger than kidney, they are going to remove the entire kidney. I guess they will test it for cancer after it's removed?


I just learned that I have a "mass" on my kidney and am scared to death. I have had no urine, no back pain or unusual fatigue. I am overweight, though. I have a CT scan Friday. How long does it take to get results?


I just discovered I have a mass on my kidney. I have also been wetting the bed lately and never have in my life. I'm only 30 and am frightened I have cancer. Is this reason to be concerned?


My five year old grandson has a 2 millimeter cyst on his right kidney. Is there a cause for extreme concern?


I have a 3.4 cm. cyst near the lower end of the right kidney. What do you think?


My doctor told me that I have a lot of cysts in both kidneys. Now what do I do?


I read that kidney biopsies are dangerous and can spread kidney cancer or give false negative readings. The article was speaking of needle biopsies taken through the back using radiologic imaging guidance.

My father has a small mass in his kidney and the urologist wants to take a biospy up through the bladder, ureter, and into the kidney. Is this a new safer method of biopsy? I have never heard of it.


@naturesgurl3 -- There are several common kidney cancer symptoms, which are generally the same as kidney mass symptoms.

First, blood in the urine can be a sign of a kidney mass and kidney cancer.

Also, persistent pain in one's side, and a lump in the abdomen near the kidneys are signs of kidney cancer.

Unexplainable weight loss and general fatigue can also be signs of kidney cancer.

However, somebody can have all these symptoms and still not have cancer -- it could be merely a mass or a cyst, or even an infection.

Even if you think you may not have kidney cancer, if you have these symptoms you should get a kidney cancer screening from your doctor asap -- better safe than sorry!


How do I know if I have a kidney tumor?

What are some of the most common kidney mass symptoms?

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