Do All Kidney Stones Travel Through the Ureters?
No, not all kidney stones travel through the ureters—many remain asymptomatic in the kidney and never enter the ureter, while others that do enter the ureter may pass spontaneously, require intervention, or remain lodged.
Natural History of Kidney Stones
Stones That Remain in the Kidney
- Many kidney stones remain asymptomatic within the renal collecting system and never enter the ureter 1
- These stones may remain stable in size, grow over time, or eventually fragment without causing symptoms
- The clinical literature focuses primarily on stones that have already entered the ureter, as these are the stones that typically cause renal colic and require medical attention 2
Stones That Enter the Ureter
When stones do migrate from the kidney into the ureter, their fate depends heavily on size and location:
Small Stones (≤5 mm):
- 68% pass spontaneously in patients under observation (95% CI: 46% to 85%) 1
- Stones ≤2 mm pass in an average of 8.2 days, with 95% passing within 31 days 3
- Stones 2-4 mm pass in an average of 12.2 days, with 95% passing within 40 days 3
- Only 4.8% of stones ≤2 mm require intervention 3
Medium Stones (5-10 mm):
- 47% pass spontaneously (95% CI: 36% to 59%) 1
- Stones 4-6 mm pass in an average of 22.1 days, with 95% passing within 39 days 3
- Medical expulsive therapy with alpha-blockers increases passage rates to 77.3% compared to 54.4% with placebo 4
Large Stones (>10 mm):
- Very low spontaneous passage rates
- 50% of stones >5 mm require intervention 3
- Urologic intervention is recommended as first-line treatment rather than observation 1, 5
Where Stones Lodge in the Ureter
Contrary to traditional teaching about three points of narrowing, stones actually lodge at two primary locations when patients present with renal colic:
- 60.6% at the ureterovesical junction (UVJ) 2
- 23.4% in the proximal ureter between the ureteropelvic junction and iliac vessels 2
- 10.6% at the ureteropelvic junction (UPJ) 2
- Only 1.1% where the ureter crosses the iliac vessels, despite this being described as a classic narrowing point 2, 6
Important finding: Proximal stones are significantly larger than distal stones (mean 6.1 mm vs 4.0 mm axial diameter), suggesting smaller stones migrate further before lodging 2
Clinical Implications
Observation Period Safety
- Ureteral stones cause obstruction and distension that typically produces at least some discomfort 1
- Complete unilateral ureteral obstruction beyond 6 weeks risks irreversible kidney injury 5
- Maximum conservative management period is 4-6 weeks from initial presentation 5
When Intervention Is Required
Stones require surgical management when:
- Size >10 mm (low spontaneous passage rates) 4
- Infection/sepsis develops 5
- Declining renal function occurs 5
- Refractory pain despite medical management 5
- No passage after 4-6 weeks of observation 5
Treatment Success Rates
When intervention is needed, ureteroscopy achieves excellent outcomes:
- 94% stone-free rate for distal ureteral stones 4
- 86% stone-free rate for mid-ureteral stones 4
- 81% stone-free rate for proximal ureteral stones 4
Common Pitfalls to Avoid
- Do not assume all kidney stones will cause symptoms—many remain in the kidney indefinitely without entering the ureter 1
- Do not wait beyond 6 weeks for spontaneous passage due to risk of irreversible renal damage 5
- Do not rely on the "three points of narrowing" teaching for predicting stone location—most stones lodge at the UVJ or proximal ureter 2, 6
- Do not offer prolonged observation for stones >10 mm—these require intervention as first-line treatment 1, 5