Spot on Your Kidney? Kidney Mass Guide | Dr. Theodore Cisu

The short answer: A "spot" on the kidney, called a renal mass, is often found by chance on a scan done for something else. Some are harmless cysts, some are benign tumors, and some are early kidney cancers that tend to grow slowly. A CT or MRI done with contrast usually tells your urologist what kind of mass it is. Depending on its size and features and on your overall health, options range from watching it with scans to removing just the tumor while saving the kidney.

Written by Theodore Cisu, MD, board-certified urologist. Based on the American Urological Association (AUA) guideline on renal mass and localized renal cancer (2021). Last reviewed November 2026.

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What is a kidney mass?

A renal mass is any growth or spot in the kidney that shows up on imaging. Many are found when you have a CT scan or ultrasound for belly pain, back pain or another reason. Finding one this way is common, and it can feel scary. The good news is that small masses found early give you and your urologist time to plan carefully.

Kidney masses fall into a few broad groups:

• Simple cysts: thin-walled, fluid-filled sacs. These are very common and almost always harmless.
• Complex cysts: cysts with walls, dividers or solid areas. Doctors grade these with the Bosniak system. Higher grades (Bosniak 3 and 4) are more likely to be cancer.
• Solid masses: these are more likely to be kidney cancer (renal cell carcinoma), though some are benign tumors such as an oncocytoma or an angiomyolipoma.

Is a spot on my kidney cancer?

Not always. A fair number of small solid masses turn out to be benign. Many small kidney cancers grow slowly, and some may never cause harm during a person's lifetime. Others are more aggressive. Sorting out which is which is the main goal of your evaluation.

Symptoms of a kidney mass

Most kidney masses cause no symptoms at all. When they do, signs can include blood in the urine, pain in the side or back, or a lump you can feel. Large tumors may cause tiredness, weight loss or fevers. If you have any of these, see a doctor.

How is a kidney mass diagnosed?

CT or MRI with contrast

The key test is a high-quality CT or MRI that takes pictures before and after contrast dye is given. This shows whether the mass "lights up" with blood flow, which suggests a solid tumor, and helps grade cysts. An ultrasound alone or a CT without contrast often can't answer the question. If your kidney function is reduced, MRI with newer contrast agents can still be used in most cases.

Blood and urine tests

These check your kidney function and look for blood or protein in the urine. Protecting your kidney function is a big part of planning.

Chest imaging

If cancer is suspected, imaging of the chest is usually done to make sure nothing has spread.

Genetic counseling

The AUA recommends genetic counseling for people with kidney cancer who are 46 or younger, people with masses in both kidneys or several masses in one kidney, and people with a personal or family history that suggests an inherited syndrome.

Do I need a kidney biopsy?

Not everyone does. A biopsy uses a thin needle, usually guided by CT or ultrasound, to take small samples of the mass. It is usually done by an interventional radiologist, and Dr. Cisu can coordinate it. The AUA guideline says a biopsy makes the most sense when the result would change your treatment. It can be helpful when:

• You are considering active surveillance and want more information about the tumor
• The mass could be something other than kidney cancer, such as lymphoma, infection or cancer that spread from elsewhere
• You are planning ablation (biopsy is done beforehand as a separate step)

Sometimes a biopsy can't give a clear answer. Your urologist will talk with you about the benefits, risks and limits before you decide.

Treatment options

The right choice depends on the size and features of the mass, your age and other health conditions, your kidney function and what matters most to you. The AUA guideline puts strong weight on shared decision-making.

Active surveillance

For small masses, especially solid masses under 2 cm and many complex cysts, watching with regular imaging is a reasonable choice. It is also often a good fit for people whose other health problems make surgery riskier. If the mass grows quickly or changes, treatment can be considered then.

Partial nephrectomy

The surgeon removes the tumor and a small rim of normal tissue and leaves the rest of the kidney in place. For small tumors, the AUA prefers saving kidney tissue when it is safe and possible, because kidney function matters for long-term health.

Radical nephrectomy

The whole kidney is removed. This may be the better choice when a tumor is large, deep in the kidney or looks aggressive, and when the other kidney is healthy and overall kidney function is good. Most people live normally with one healthy kidney.

Robotic kidney surgery

Dr. Cisu performs robotic partial and radical nephrectomy. The surgery is done through several small incisions in the belly using a robotic system. Many people go home after a short hospital stay, though recovery is different for everyone.

Thermal ablation

Ablation destroys a small tumor with extreme cold or heat delivered through a needle, usually placed through the skin by an interventional radiologist. The AUA considers it an alternative for solid tumors under 3 cm. Tumors may be more likely to come back in place than after surgery, and repeat treatment is sometimes needed. Your urologist can discuss whether it fits you, and Dr. Cisu can coordinate a referral.

What happens after treatment?

Follow-up includes regular visits, blood tests and imaging of the belly and chest. How often depends on the type and stage of the tumor and the treatment you had. If the tumor had a higher risk of coming back, you may be referred to a medical oncologist to discuss treatment after surgery.

When to see a urologist

• A CT, MRI or ultrasound report mentions a renal mass, solid lesion, complex cyst or Bosniak 2F, 3 or 4 cyst
• You have blood in your urine
• A family member had kidney cancer at a young age, or you have a known inherited syndrome

A simple cyst usually needs no urologic follow-up. If you aren't sure what your report means, a urologist can review it with you.

Seeing Dr. Cisu for a kidney mass

If a scan has found a spot on your kidney, you can start with a telehealth visit from anywhere in Virginia. Our office can request your CT, MRI or ultrasound images and reports so Dr. Cisu reviews them before you talk. Second opinions are welcome. In-person visits are available at our clinics in Charlottesville and Fishersville, and no referral is needed. Book an appointment.

Frequently asked questions

Should I be worried about a spot on my kidney?

It's normal to worry. Many kidney spots are simple cysts or slow-growing masses, and small ones found early usually leave time to get the right tests and make a careful plan. A urologist can tell you which group yours falls into.

How fast do small kidney tumors grow?

Many small kidney masses grow slowly, often over years, which is why active surveillance is an option for some people. Growth rates vary, so regular imaging is needed to track any change.

Can a kidney mass be watched instead of removed?

Yes, for many small masses. Active surveillance is a reasonable choice for small solid masses, many complex cysts and people with other serious health problems. The plan includes scheduled imaging and a switch to treatment if the mass changes.

Can I live with one kidney?

Yes. Most people live a normal life with one healthy kidney. Your doctor will check your kidney function over time and may suggest steps to protect it, such as controlling blood pressure.

Is partial nephrectomy better than removing the whole kidney?

Each has a place. For small tumors, saving the kidney helps protect long-term kidney function. For larger or more complex tumors, removing the whole kidney may be safer. The choice depends on the tumor, your kidneys and your health.

What does Bosniak 3 mean?

Bosniak is a grading system for kidney cysts. A Bosniak 3 cyst has thick walls or dividers that light up with contrast. It has a meaningful chance of being cancer, so it is managed like a possible tumor and discussed with a urologist.

Sources

• American Urological Association. Renal Mass and Localized Renal Cancer: Evaluation, Management, and Follow-Up: AUA Guideline (2021).
• American Urological Association. AUA Announces Updates to Clinical Guidance for Renal Mass and Localized Renal Cancer (2021).

This article is for general education and isn't a substitute for medical advice. Talk with your own doctor about your imaging results and options.