Here’s a common scenario: you go for an imaging test – CT scan, ultrasound or MRI – and your report says you have a renal mass. It sounds scary, but what does it mean? A mass on your kidney can be several things. Often, it’s what’s called a simple cyst - a harmless fluid bubble. Sometimes it’s a complex cyst, which may need to be monitored and can be treated if necessary. Or the mass could be cancerous. Fortunately, most kidney cancers are curable, says Timothy D. Averch, MD, Chief of the Division of Urology at Prisma Health-Midlands in Columbia, South Carolina.
Most kidney cysts and kidney cancers are found when a person has an imaging test for something else, Dr. Averch said. “In general, neither kidney cysts nor tumors cause symptoms, especially when they’re smaller. That means people don’t even know they have something on their kidney unless they have a scan for some other reason.”
What is a kidney cyst?
As a person ages, sacs filled with fluid, called cysts, can form in the kidneys. They are usually small. Some people have one cyst, while others have many. Cysts can be found in one kidney or both kidneys. The sacs can range in size from a pea to a softball.
Most cysts are simple cysts. They are not cancerous. They do not enlarge the kidneys or affect their function. Simple kidney cysts are more common in people over 50. They are more common in men than in women. It is not known what causes the cysts.
When seen on an imaging test, simple kidney cysts have smooth, well-defined and rounded edges. This helps the doctor tell them apart from kidney tumors.
Kidney cysts don’t usually cause symptoms and don’t need to be treated. If your cysts are causing symptoms, your doctor may drain them with a procedure called aspiration. The doctor uses ultrasound as a guide to insert a long needle through the skin and into the cyst. The doctor drains the cyst to remove all of the fluid. Sometimes medication is injected into the cyst which can harden the inside of the cyst so it is less likely to fill up with fluid again. Larger cysts that are causing symptoms may be treated with laparoscopic surgery where the outer layer of the cyst is removed so that it cannot fill with fluid.
Another less common type of cyst is called a complex cyst. These cysts appear different on an imaging test. They may have thickened edges, or calcium deposits in them instead of fluid, Dr. Averch said. These cysts can be associated with cancer. They either need to be monitored with regular imaging tests or treated.
“In many cases, if the complex cyst is less than 4 centimeters, the doctor will recommend ‘active surveillance.’ This means following the cyst with more imaging tests three months later to see if there’s any change. If it grows, that may be a sign of cancer.”
If the complex cyst is over 4 centimeters, the doctor may treat it by removing the cyst (not the whole kidney). Another treatment option may be cryotherapy. Extreme cold is used to destroy the cyst. A hollow needle is inserted into the cyst. Very cold gases are passed through the needle. This creates an ice ball that destroys the cyst.
Kidney cancer
In some cases, an imaging test shows or suggests the mass on a kidney is cancerous. “It can be challenging to tell the difference between a complex cyst and a tumor,” Dr. Averch said. One clue is whether the mass has blood vessels supplying it. This is a sign the mass is cancerous.
If the tumor is less than 2 centimeters, the doctor may suggest active surveillance. If it is over 4 centimeters, the doctor will likely recommend surgery to remove it. “The doctor will make a recommendation on many factors. These include how big the tumor is and how quickly it is growing. We also consider a patient’s age and overall health,” Dr. Averch said. “A very young patient will likely have the tumor removed. An elderly patient with other medical problems may not.”
Kidney stones
Unlike kidney cysts or kidney cancer, kidney stones often do cause pain. If you have pain in your side, and the cause is your kidney, it’s most likely to be a kidney stone or infection, Dr. Averch said. Kidney stones are hard, pebble-like pieces of material that form in one or both of your kidneys when high levels of certain minerals are in your urine. A small kidney stone may pass through your urinary tract on its own, causing little or no pain. A larger kidney stone may get stuck along the way. A kidney stone that gets stuck can block the flow of urine. This can cause severe pain or bleeding.
Treatment depends on the type of stone you have, its size, location, and how long you have had symptoms. Options include:
- Waiting for the stone to pass by itself. Often you can simply drink more water and wait for the stone to pass. Smaller stones are more likely than larger stones to pass on their own.
- Medication. Certain medications have been shown to improve the chance that a stone will pass.
- Surgery. Surgery may be needed to remove a stone from the ureter or kidney if:
- The stone fails to pass on its own.
- The pain is too great to wait for the stone to pass.
- The stone is affecting kidney function or infection is present.
Whether it’s a cyst, stone or even a tumor on your kidney, with proper care the outcome is likely to be good, Dr. Averch said. “In this day and age, when patients can read their radiology results online, it’s scary to see the words ‘renal cyst’ or ‘renal mass.’ It’s important to recognize that most cysts don’t need any treatment. If they’re complex, they can be followed and treated if necessary. And these days, kidney cancer, especially when it’s small, is often curable.”