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Does Stone Size Matter?

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The reason I decided to write on this topic was because of this Instagram post. I stated that,

“renal stones over 10mm or those which have not passed after 4 – 6 weeks will require lithotripsy or ureteroscopy”

Well, there were a lot of replies stating that the cutoff is 5mm. So, lets look at the literature.

Before we get there I want to make sure to let everyone know I’m glad people are voicing their opinions! Question everything – don’t be scared to question an attending, professor, or someone more senior. If you feel like they are wrong, speak up!

Ok, back to the topic at hand…

Stone passage depends on: size and location. Smaller and more distal stones are more likely to pass without intervention – this is obvious and I’m sure we can all agree, right? Right.

According to Uptodate:

“Most stones ≤5 mm in diameter pass spontaneously. For stones larger than 4 mm in diameter, there is a progressive decrease in the spontaneous passage rate, which is unlikely with stones ≥10 mm in diameter. Proximal ureteral stones are also less likely to pass spontaneously.”

So, after 5mm, the likelihood that the stone will pass spontaneously begins to decrease – this does not mean, however, that immediate intervention is required! This simply means that the likelihood of needing that intervention increases.

An easy rule of thumb is that 5mm stones have a 50% chance of passing – so it’s a crap shoot (could go either way).

Less than 5mm = more likely to pass
More than 5mm = less likely to pass

Medscape says:

“In general, stones that are 4 mm in diameter or smaller will probably pass spontaneously, and stones that are larger than 8 mm are unlikely to pass without surgical intervention. With MET, stones 5-8 mm in size often pass, especially if located in the distal ureter. The larger the stone, the lower the possibility of spontaneous passage (and thus the greater the possibility that surgery will be required), although many other factors determine what happens with a particular stone.”

Again, no surgical intervention is needed in stones under 8mm (per them). They only state that the likelihood of spontaneous stone passage decreases after 5mm.

Now, lets look at the International guidelines from the American Urological Association and the European Association of Urology on the management of ureteral calculi:

“In a patient who has a newly diagnosed ureteral stone <10 mm and whose symptoms are controlled, observation with periodic evaluation is an option for initial treatment. Such patients may be offered an appropriate medical therapy to facilitate stone passage during the observation period. In a choice between active stone removal and conservative treatment with MET, it is important to take into account all individual circumstances that may affect treatment decisions. A prerequisite for MET is that the patient is reasonably comfortable with that therapeutic approach and that there is no obvious advantage of immediate active stone removal”

Again, they are stating the same. If the patient is STABLE and the stone is under 10mm, then there is no reason to do any more than MET, pain control, hydration, and observation. Now if the stone doesn’t pass after 4-6 weeks, but is less than 10mm in size (let’s say 5 mm), then you should refer to urology – this is also an indication for intervention.

This is an example of miscommunication, in my opinion. I feel students misunderstood likelihood of passage with surgical intervention requirements. These keywords are really important. So, I stand by my answer – if there are still people who feel I am incorrect, shoot me an email. I’d love to get your thoughts!

Talk Soon.
Andrew