Most physicians feel that crystals only cause issues if they are blocking the ureter and/or passing down towards the bladder. Calcium oxalate crystals that are not obstructing, such as those located in the kidney’s calyxes, are generally thought to not cause issues. This explains why some patients can have extremely large crystals filling up their entire kidney with no or minimal issues. It is believed however that some non-obstructing calcium oxalate crystals can cause issues because they either block a small tubular structure in the kidney itself (the collecting tubules) or for other unclear reasons. Supporting this view is a recent medical journal article suggesting that the treatment of small non-obstructing “papillary” crystals may provide relief. (Gdor et al, Multi-institutional assessment of ureteroscopic laser papillotomy for chronic pain associated with papillary calcifications, J Urol 2011)