Can You Experience Nephrolithiasis Pain Without Stones on Ultrasound?
Yes, patients can absolutely experience intermittent renal colic pain from kidney stones even when ultrasound shows no evidence of stones—this occurs in 43-76% of cases because ultrasound has poor sensitivity (only 24-57%) for detecting stones, particularly small ones.
Why Ultrasound Misses Stones
Ultrasound has significant limitations for stone detection:
- Gray-scale ultrasound detects only 24-57% of renal calculi compared to CT, with even worse performance for smaller stones 1
- Ureteral stones are particularly difficult to visualize, with sensitivity up to only 61% (though specificity is 100% when stones are seen) 1
- Even with color Doppler and twinkling artifact assessment, which can improve sensitivity to 99% for stones <5 mm, the false-positive rate reaches 60% 1, 2
When Stones Exist Despite Normal Ultrasound
Several clinical scenarios explain stone-related pain with negative ultrasound:
- Small stones (<5 mm): These are frequently missed on ultrasound but can still cause significant intermittent pain as they move through the collecting system 1, 2
- Ureteral location: Stones in the ureter are notoriously difficult to visualize on ultrasound, with detection rates far below those for renal stones 1
- Early presentation: Within the first 2 hours of symptom onset, secondary signs of obstruction (hydronephrosis) may not have developed yet, making detection even more challenging 1, 2
- Recently passed stones: The stone may have already passed by the time of imaging, but pain can persist from ureteral inflammation or edema 1
The Hydronephrosis Pitfall
Absence of hydronephrosis does NOT rule out stones:
- While ultrasound is 100% sensitive and 90% specific for detecting ureteral obstruction (hydronephrosis), this finding fails to predict the presence or absence of ureteral stones in up to 25% of patients 1
- Hydronephrosis on ultrasound has only a 77% positive predictive value and 71% negative predictive value for actual stone presence 3
- Non-obstructing stones (particularly small ones) can cause significant intermittent pain without causing hydronephrosis 2
What To Do Next
If clinical suspicion remains high despite negative ultrasound, proceed to noncontrast CT:
- Noncontrast CT is the reference standard with 97% sensitivity for detecting stones of any size 1, 2, 4
- Low-dose CT protocols maintain 97% sensitivity while minimizing radiation exposure 2
- CT reliably detects stones as small as 1 mm and accurately characterizes location and size 1
- This is particularly important if the patient has a prior history of nephrolithiasis, which increases the likelihood of recurrent stones by 3.3-fold 5
Clinical Bottom Line
Do not rely on ultrasound alone to exclude nephrolithiasis in patients with classic renal colic symptoms. The combination of intermittent flank pain, hematuria, and prior stone history warrants CT imaging even with a normal ultrasound, as ultrasound misses nearly half of all stones 1, 2. The absence of stones on ultrasound should be interpreted as "stones not visualized" rather than "no stones present."