Simple kidney cysts are fluid-filled sacs that form in your kidneys. These cysts usually don't affect how the kidneys function. The kidneys are two bean-shaped organs located just under your ribcage on each side of your spine. They filter large amounts of blood each day. They also help regulate the fluid and salts (electrolytes) in your blood. They release waste products through your urine.

Simple kidney cysts are very common and rarely need treatment. Most people don't even know that they have them. You might have a single kidney cyst. Or you might have more than one. You might have them on only one kidney or on both of them. Most commonly, you'll have only a single cyst. Over time, the cyst might slowly increase in size. They can range from the size of a pea to a golf ball.

Simple kidney cysts become more common in those older than age 50, but they may be present at birth. Men get these cysts more often than women. As medical imaging becomes more frequent, more and more people are diagnosed with these cysts.

Simple kidney cysts are different from complex kidney cysts. Doctors can identify the type of cyst based on its appearance with medical imaging. Simple kidney cysts are the most common type. These cysts have thin walls and a regular, rounded shape. They're filled only with fluid. In contrast, a complex kidney cyst might have thicker walls and an irregular shape. It might also contain solid material. A complex kidney cyst may be a sign of cancer. But a simple kidney cyst isn't cancerous.

Researchers are still not sure what causes simple kidney cysts. The kidneys have tiny tubules. These structures collect newly formed urine. Cysts may result when the tubules get blocked. Small sacs sometimes form on the tubules. These may detach and become simple kidney cysts.

Some medical conditions can cause kidney cysts to grow. For example, a person with polycystic kidney disease develops a large number of kidney cysts. (The cysts may be simple or complex.) Too many cysts can prevent the kidney from working correctly.

Other medical conditions that can cause simple or complex kidney cysts include:

• Chronic kidney disease from any cause (especially with dialysis)
• Medullary cystic kidney disease
• Autosomal dominant polycystic kidney disease
• Von Hippel-Lindau disease
• Tuberous sclerosis complex

Doctors don't fully know what causes simple kidney cysts, but they're more common as people age.

Most people don't notice any symptoms from their simple kidney cysts. Rarely, they may become large enough to cause:

• Blood in your urine (if the cyst bursts)
• Pain in your upper belly or back (if the cyst bursts)
• Fever and chills (if the cyst becomes infected)
• Elevated blood pressure (if the cyst compresses the kidney)
• Problems passing urine (if the cyst blocks the ureter, the tube that passes urine from the kidneys to the bladder)
• A mass detected on a physical exam

Simple kidney cysts usually don't affect kidney function unless they block the flow of blood or urine.

Simple kidney cysts are often first found with an imaging test that was done for another reason. Your doctor will perform a medical history. They will ask about your recent symptoms and past medical problems. You'll also need a physical exam.

It is important to distinguish simple kidney cysts from complex cysts. Complex cysts might be cancerous. They usually need to be removed. For this reason, your doctor might order medical imaging tests like:

• Kidney ultrasound
• Kidney CT scan (if more detail about the cyst is needed)
• Kidney MRI (if the nature of the cyst is still unclear)

A radiologist will look at these images to see if your kidney cyst is simple or complex. Doctors sometimes rate cysts using 5 categories, which are I, II, II-F, III, and IV. These are based on complexity and the possibility that it may be cancerous. If your cyst is ranked a category I cyst, you probably won't need any more imaging. Kidney cysts with higher ratings might need more imaging or treatment. Category IV cysts are most often linked with cancer.

Your doctor will also check for other conditions that may be causing the cysts. If the diagnosis is still unclear after medical imaging, you might need to have genetic testing. It can help rule out other conditions, such as polycystic kidney disease.

Many people with simple kidney cysts don't need treatment. Doctors may want to closely watch the cysts. You may need occasional ultrasounds of the kidneys.

If you have symptoms, or if the cyst is blocking the flow of urine, you might need one of the following treatments:

• Sclerotherapy, a procedure to puncture the cyst with a long needle put through the skin
• Surgical procedure to drain the cyst and remove its outer tissue
• Antibiotics and drainage to treat a kidney cyst infection

Contact your doctor right away if you start having possible symptoms from your kidney cyst. These may include blood in your urine, pain in your back, or problems passing urine.

• Simple kidney cysts are fluid-filled sacs that form in your kidneys. Though abnormal, these cysts usually don't affect how your kidneys work.
• Most simple kidney cysts don't cause any symptoms. They also usually don't need any treatment.
• Using medical imaging, your doctor can tell if your cyst is simple or complex. A complex cyst might be cancerous.
• You may need repeat imaging to keep track of your simple kidney cyst.
• If your cyst causes symptoms, you may need to have it removed.
• If you have many kidney cysts, you may need testing to see whether you have a condition causing them. One such condition is polycystic kidney disease.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you don't take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours and on weekends and holidays.