Benign ( enlarging ) cyst on kidney

A renal ultrasound shows a slightly enlargening benign cyst in the right kidney, my  only kidney, left kidney removed due to cancer in 1981.
What is the cause of such a cyst ? Treatments? How fast will it grow ?
Can it lead to cancer ?
I have no pain. Take baby aspirin daily along with 10 mg lisinopril for slightly high Blood pressure.---only meds--

[Stephen Liroff, MD]

A kidney cysts is basically a bag of  fluid that is on the surface or interior of a kidney. These occur more frequently as we  get older and are rarely of any consequence.. If the cyst meets the specific  ultrasound criteria for diagnosing a cyst, then further work-up need not  be pursued. These would not be expected to degenerate into cancers nor would they be expected to resolve. They may be stable or enlarging and are reported to affect kidney drainage (and thereby, function) in rare instances, depending upon  their location Also, rarely, they may cause pain and need to be opened surgically and drained. The need for any intervention is very uncommon and often further ultrasounds or CT scans are not necessary. The cause for such cysts  is  unknown  and the speed of growth is unpredictable.
I realize your concern with a single kidney and your history of renal cancer, but I would not worry. At most you might consider a repeat ultrasound in another 6-12 months to help set your mind at ease.
S.A.Liroff, M.D.

[Jim878]

Thank you ,

Very helpful, I am scheduled to see a Nephrologist in Jan for further tests,and discussion. My primary doctor does not see an urgency or concern as you state.

Jim878