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Urology/Kidney Cyst Complications and Proteinuria


QUESTION: I'm a 75 yo w/m with 7 cm simple left kidney cyst (small calcification). This cyst has grown from approx 4 cm in past three yrs. I have Type II diabetes but take no meds or insulin. I have a copy of a recent CT.

Several questions:

1) I've become aware -- am starting to "feel" -- the cyst in left flank for past several months. It doesn't hurt. Just a definite feeling of pressure that was not there in the past. Is this a normal development or a cause for concern? If the pressure is a warning, I need to know.

2) If the cyst ruptures, do the contents (fluid) excrete with the normal urine or remain inside the kidney and cause problems? In other words, could the cyst possibly empty itself and shrink without causing complications.Is a simple cyst rupture always a medical emergency?

3. My eGFR has dropped to 53 from 59 and I have some microalbumin 30.0 ug/mL in latest test. Creatinine serum is 1.31. BUN/Creatinine ratio is 15. I'm concerned that the large cyst could be causing glomerular scarring resulting in protein leakage. I have not had proteinuria on earlier tests.

4. I've read that if sclerotherapy (drainage) is performed there is a high likelihood of recurrence (50%?). Is that true? If there's recurrence, how fast are we talking -- months, years? When there's a recurrence does that mean the old cyst just fills up with fluid again or does it mean a new one forms?

ANSWER: Tom, simple renal cysts are exceedingly common and almost always benign. Most are discovered incidentally by imaging studies such as ultrasound, CT scan or MRI.  There are established radiologic criteria for denoting a lesion as a simple benign cyst.  However, some tumors may appear similar to cysts and these are termed "complex cysts".   If there is any question of a cyst being benign, further investigation is needed using another or all of the imaging studies noted above.  If there is still doubt, either aspiration of the "cyst" fluid for cytologic examination, biopsy or open surgical exploration is indicated.

Renal cysts may occur inside of the kidney (intra-renal) or come off the external surface of the kidney (exophytic).   They almost never cause symptoms and, therefore, this type does not require treatment.  Rarely, they may become quite large and compress surrounding structures.  If so, they may cause discomfort (either type) or obstruct urine flow (usually from the intra-renal variety) from the kidney. In these cases, treatment is indicated.  This may take the form of needle aspiration alone (which provides only temporary relief as the fluid always recurs), aspiration with the instillation of a sclerosing agent (which damages the lining of the cyst to prevent it from re-secreting fluid) or surgical removal of the cyst (leaving the kidney intact).  

if a cyst ruptures, the fluid is absorbed by the surrounding tissues and generally causes no problem.  The fluid more often than not, gradually recurs.  I  am not concerned about your slightly lower eGFR or mild proteinuria especially with perfectly normal serum creatinine and BUN.  

Ido not think your cyst is interfering with your renal function unless there was evidence of obstruction on your imaging study.  

After sclerotherapy, the fluid can recur over but  a very variable period of time.  I would not suggest this be done unless there is evidence of obstruction or significant pain related to the cyst (which is unusual).   

Good luck.

---------- FOLLOW-UP ----------

QUESTION: Thanks very much for your taking time to look at my questions. I do have a followup. My cyst is intrarenal. I believe that years ago on a CT the total length of the left kidney was shown to be 9 cm. Having grown from 4 cm to 7 cm in the past four years, which seems to me to be very fast, my cyst is now almost as large as the kidney. I have a mental image of a balloon being blown up until it gets so big it explodes. Do these cysts ever slow down or stop expanding?

I've read about the Bosniak scale for classifying cysts. I think mine is either Bosniak 2 or Bosniak 2F. A CT last year said "calcification along the posterior aspect is seen, 5.6 mm." I know how long 5.6 mm is (not long) but would like to know whether it is "long" in the context of calcium on a simple cyst. I have no frame of reference.

Saying that it is situated "along" the posterior aspect sounds to my layman's ears like it describes length along the wall of the cyst as opposed to thickness through the wall (if that matters). Am I on the right track here?

Tom, cysts often do stop expanding, especially those that are intrarenal.  I believe your interpretation of the Bosniak classification is correct because of the calcification of its posterior wall.  This would be 5.6 mm linearly in the wall.  As you note from the classification, the presence of calcium does increase the risk of malignancy a bit.  Because of this & the fact that you are somewhat symptomatic,  it might be reasonable to have the cyst aspirated and have the fluid sent for cytology.  The pros and cons of instilling a sclerosing agent can be discussed beforehand with your urologist.  Good luck.


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Arthur Goldstein, M.D.


Problems or questions related to the field of urology; ie urinary stone disease, urinary cancers (kidney, bladder, prostate, testis, etc.), urinary infections, etc. I no longer answer questions related to erection problems or male sexual dysfunction.


I am retired from the active practice of urology. My 34 years was totally in the clinical field and involved the entire gamut of genitourinary problems, with special interest in endourology.

American Medical Association, American Urological Association, American College of Surgeons

College degree - BS Medical degree - MD Master of Science - MS

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