In our “Ask a kidney stone doctor” section, we field questions from stone formers or their family members. Today’s question is about small non-symptomatic kidney stones. See other questions and answers or ask your own question here.
July 22, 2011
Question from Minnesota:
I have a 3mm to 4mm stone in my right kidney, which has been there since 2003. It originally was very high up in the kidney, but moved to the lower part of the kidney in 2006. I just had another CT done, and it is still in the same place and the same size. Because the stone is in the lower part of the kidney versus the higher part, is it less likely to pass, because it would have to go up to get into the ureter versus down? Because I’ve had this stone so long with no changes, what are the chances that it will just continue to sit there and never pass? It has caused me no pain other than occasional blood in my urine. I was told by my doc that I could wait and watch the 3-4mm stone in my right kidney or proceed with ureteroscopy to remove it. It’s been sitting there since 2003 without giving me any discomfort. How painful is having a stent put in to promote healing after the ureteroscopy and is it really necessary?
Many patients are found with small stones and it can be confusing deciding on whether to proceed with treatment or to continue observing the stone(s). Several factors need to be considered to help make a decision:
1) Size: Stones that are smaller than 5mm are more likely to be able to pass successfully without requiring surgery. When a stone is larger (>6mm) and unlikely to pass successfully, it may make more sense to intervene. In your case, the stone is small and if it were to start moving down the ureter, it would have a good chance of passing spontaneously. However, successful passage does not mean non-painful passage as even small stones can cause significant discomfort when they move down the ureter. Because of this, patients who have already experienced a stone episode in the past are usually more motivated to have an early intervention so that they can avoid another stone passage episode.
2) Stability: Stones that are growing are more likely to lead to problems while stones that stay the same size are less likely to become symptomatic. As your stone is stable over 8 years, one could argue to continue to watch it.
3) Location: Stones that are not obstructing, like yours, are generally asymptomatic. Stones that are floating in the renal pelvis or ureter are more likely to cause obstruction and more likely to require intervention. Stone fragments in the lower pole are generally felt to be less likely to pass. However, in addition to whether the stone is in the upper pole, middle-pole, or lower pole of the kidney, researchers have focused on the “calyceal anatomy” which can be though of as the length of the “tunnel” and the angle of the “tunnel” that the stone would have to travel to end up in the center part of the kidney where it could start making its way down the ureter.
4) Symptoms: Stones that cause symptoms such as pain, recurrent infections, or significant bleeding would be more likely to require intervention than stones that are causing minimal symptoms.
5) Other things to consider: Certain individuals will be advised to have their stone treated even if it is small and asymptomatic. This includes pilots, who would put themselves and their passengers at risk if they were to experience a stone passage episode while flying, and travelers to remote locations, where modern medical facilities may not be available if they were to suffer a stone attack.
The short answer as to how likely your stone is to remain there without causing problems is 80% over the next 3-10 years. Another way of looking at this is that 20%, or 1 out of 5 patients in your situation will experience a stone passage episode over the next 3-10 years while 4 out of 5 will do fine without experiencing problems. Here’s the long answer: Based on a study of 5,047 adults who underwent CT colonography screening, asymptomatic stones, such as yours, are found in 8% of American adults. In that study, the average stone size was 3mm. Over 10 years, 20.5% of patients with stones, or 1 out of 5, developed a symptomatic “stone episode” requiring intervention. Alternatively, 4 out of 5 patients did fine without experiencing a stone episode. This rate of 20% of small stones requiring treatment when observed is remarkably consistent with multiple other studies where patients with small stones were observed.
Finally, as to your question about ureteral stents, stents are often required after ureteroscopy surgery because of the ureter’s tendency to swell temporarily and become blocked after this type of surgery. This swelling can cause pain similar to a stone episode. We’ve found that this is more likely to occur in patients who have not had prior ureteroscopy surgery. Note though that this is a “surgeon’s preference” as some urologists will be more likely to perform ureteroscopy without leaving a stent. Stent pain can be mild or can be very uncomfortable. While some patients do not even realize a stent is there, most can’t wait to have them removed and some patients will say that the stent was worse than their stone. One way to potentially avoid a stent is to consider shockwave lithotripsy (ESWL) if the stone is easily visible on a plain x-ray.