Objective: To determine the natural history of observed nonobstructing asymptomatic kidney stones and factors associated with eventual stone-related events.

Design: Retrospective chart review of the records of 160 kidney stones in 110 patients on active surveillance.

Methods: Stone characteristics, patient characteristics, and stone-related parameters were evaluated to determine factors for stone-related symptoms, spontaneous passage, requirement for surgical intervention, and stone growth.

Results: 160 stones with an average size of 7.0 mm ± 4.2 mm in 110 patients were followed up 41 ± 19 months. A total of 28% (45 of 160) of stones caused symptoms and 2% (3 of 160) caused silent obstruction on average of 37 ± 17 months. Upper-pole/mid-pole stones were more likely than lower-pole stones to become symptomatic (40%) or pass spontaneously (15%). No other factors demonstrated statistical significance in predicting symptoms.

Conclusions: Over a 3-year period, most asymptomatic nonobstructing renal calculi remained asymptomatic. Approximately 30% caused symptoms, 20% required surgical intervention, 20% grew >50% initial size, and 7% passed spontaneously. Lower-pole stones caused fewer issues than upper- or mid-pole stones. Silent obstruction may occur and necessitates regular imaging and follow-up of even asymptomatic stones.

Reviewer’s Comments: This is a very nice article following the natural history of asymptomatic nonobstructing kidney stones, which are often picked up on imaging for other indications. It shows almost identical results to previous studies, which is that over a specified period (average of 3 years in this study), approximately 30% of stones will become symptomatic or need intervention. In this study, however, if you account for patients (instead of stones), nearly 40% became symptomatic over the study period. One must also consider that 20% of stones in this study grew >50% their original size. A small percentage developed silent obstruction, which is the most concerning aspect in regard to possible renal function loss. The authors conclude that most stones remain asymptomatic over time and hint that active surveillance may be the best option. The authors make a very valid point. However, the debate becomes whether you and your patient consider 30% to 40% as an acceptable number. Are we really saving 70% of individuals from needed intervention or having symptoms, or are we just delaying the inevitable? With the exception of uric acid stones, which may dissolve, stones do not disappear. I think with longer follow-up, more will eventually become symptomatic. Whether you treat prophylactically or only treat history of kidney stones, and lifestyle. Overall, this is a nice article to provide numbers to patients in regard to nonobstructing asymptomatic kidney stones.(Reviewer–David A. Duchene, MD).