Kidney Cysts: To Worry Or Not?

Andrew Siegel M.D.  12/16/17

You may have had some sort of chest or abdominal imaging study and you were told that you have one or more cysts in your kidney(s). Is this any reason for concern?

Kidney cysts, a.k.a. renal cysts, are round sacs filled with fluid located within or attached to the kidney. Most are not symptomatic nor dangerous and are discovered incidentally on imaging studies (ultrasound, computerized tomography, or magnetic resonance imaging) done for other reasons.

Renal cysts are common, occurring in 25% or so of adults over age 40 and 50% of adults over age 50. They are quite variable in size, ranging from smaller than a pea to larger than a cantaloupe.  Most are defined as simple cysts: spherical, thin walled, fluid-filled, without septa (internal divisions), without calcification, without solid parts, and do not take up contrast on imaging studies. Although large cysts may become symptomatic by compressing adjacent organs, this is extremely unusual. Only under the rarest of circumstances do simple cysts require treatment or intervention.

Note: In my more than 25 year urology career I have only needed to remove simple cysts in two patients.  Both were slender women, one with a cyst so large that it distorted her abdomen, as if she was pregnant.  The other woman had the cyst located behind her stomach, displacing her stomach upwards towards her abdominal wall such that every time she ate, she could actually see the bolus of food moving from her stomach down her intestine.

Ultrasound (sonography) is a non-invasive imaging technique that does not require radiation nor contrast injection and is used for determining the number, location, and size of cysts and is also an excellent means of following cysts over time.

The following image is an ultrasound of a simple renal cyst:


Attribution: © Nevit Dilmen [CC BY-SA 3.0 ( or GFDL (, via Wikimedia Commons

Although most renal cysts are classified as simple cysts, there are cysts in the kidney that may be more complex, and on occasion a cyst can be malignant. If a cyst has a thick wall, internal components (septa), calcifications, or it enhances with contrast, it is not classified as a simple cyst, but as a complex cyst.

Renal cyst classification uses the Bosniak system, named for Dr. Bosniak, the radiologist who devised it:

I   Simple benign cyst: Hairline-thin and smooth wall and no septa, calcifications, or solid components. It has the tissue density of water and does not enhance with contrast. Malignancy potential: highly unlikely.

II Mildly complex benign cyst: May contain a few hairline septa, calcification may be present in the wall or septa, but no enhancement with contrast. Malignancy potential: 0-10%.      

IIF (F = follow-up) Moderately complex cyst: May contain hairline septa, minimal enhancement may be seen in the wall or septa and may contain calcifications. No soft tissue enhancing elements present. Malignancy potential: 5-25%.      

III Indeterminate complex cyst: Cystic mass that has thickened irregular walls or septa in which enhancement is present; should be explored surgically, although some will prove to be benign, including hemorrhagic cysts, chronic infected cysts, and multi-loculated cystic nephroma, while some will be malignant including cystic renal cell carcinoma. Malignancy potential: >50%.      

IV Complex cystic mass: Malignant cystic masses that have thickened and irregular walls and septa that enhance and also contain enhancing soft tissue components. These include cystic carcinomas and require surgical removal. Malignancy potential: > 90%.     

Bottom Line: The vast majority of renal cysts are picked up incidentally (on imaging studies done for other reasons) and are simple benign cysts (Bosniak I) that will never cause symptoms or problems. They are amenable to follow up with ultrasound and rarely require intervention. The answer to the question about whether or not to worry about cysts is usually: “Not to worry.”

Wishing you the best of health,

2014-04-23 20:16:29

A new blog is posted weekly. To receive a free subscription with delivery to your email inbox visit the following link and click on “email subscription”:

Dr. Andrew Siegel is a physician and urological surgeon who is board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  He is an Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro Area, Inside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community.

Dr. Siegel has authored the following books that are available on Amazon, Apple iBooks, Nook and Kobo:

 MALE PELVIC FITNESS: Optimizing Sexual & Urinary Health

THE KEGEL FIX: Recharging Female Pelvic, Sexual and Urinary Health 

PROMISCUOUS EATING: Understanding and Ending Our Self-Destructive Relationship with Food


These books are written for educated and discerning men and women who care about health, well-being, fitness and nutrition and enjoy feeling confident and strong.

Dr. Siegel is co-creator of the male pelvic floor exercise instructional DVD (female version is in the works): PelvicRx

Tags: , , , , ,

One Response to “Kidney Cysts: To Worry Or Not?”

  1. Little Tumors in the Kidney: Challenges and Solutions | Our Greatest Wealth Is Health Says:

    […] studies are capable of diagnosing and evaluating solid renal masses and distinguishing them from fluid-filled cysts, neither study is capable of distinguishing benign from […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: