Can ureteric calculi be detected when the bladder is not full?

Ureteric Calculi Detection Independent of Bladder Filling Status

Yes, ureteric calculi can be reliably detected regardless of bladder filling status, as the detection of stones in the ureters does not depend on bladder distension. The imaging modality used determines detection accuracy, not bladder volume.

Imaging Modality Performance for Ureteric Calculi

Noncontrast CT (Gold Standard)

• Noncontrast CT is the reference standard for detecting ureteric calculi with sensitivity up to 97%, and bladder filling status is irrelevant to its diagnostic accuracy 1.
• CT directly visualizes calculi throughout the entire ureter from the ureteropelvic junction to the vesicoureteric junction, independent of urinary tract opacification 1.
• Low-dose CT protocols maintain 97% sensitivity while reducing radiation exposure, making this the preferred approach for stone detection 2.
• Detection accuracy decreases only with smaller stone size (<3 mm), not with bladder volume 1.

Ultrasound Limitations

• Gray-scale ultrasound has poor sensitivity (24-57%) for detecting renal calculi and even worse performance for ureteral stones (up to 61% sensitivity) 1, 2.
• Ultrasound detection of ureteral calculi is reduced compared to CT regardless of bladder filling, though sensitivity improves when secondary signs of obstruction (hydronephrosis) are present 1.
• Within the first 2 hours of symptom onset, secondary signs of obstruction may not have developed yet, further limiting ultrasound utility 1.
• The addition of color Doppler with twinkling artifact can improve sensitivity for small renal stones, but has a false-positive rate up to 60% 1.

Clinical Context for Imaging Selection

• For acute flank pain with suspected ureteric calculi, noncontrast CT of abdomen and pelvis should be obtained, as it provides comprehensive evaluation of the entire urinary tract independent of bladder status 1.
• CT imaging should include the pelvis to detect stones in the distal ureters and bladder, though bladder distension is not required for stone visualization 1.
• Ultrasound should be reserved as first-line imaging only for pregnant patients, pediatric patients, or those with renal impairment to avoid radiation or nephrotoxic contrast 2.

Stone Location and Detection Patterns

• Stones in the middle and lower ureter that are not visible on plain radiography or ultrasound are commonly detected by CT, with these stones tending to be smaller (mean 3.77 mm vs 6.37 mm for stones visible on conventional imaging) 3.
• Over 95% of small ureteric stones undetected on plain radiography and ultrasound pass spontaneously after conservative therapy, but CT remains necessary for definitive diagnosis 3.
• Ultra-low-dose CT (0.8 mSv) provides diagnostic quality imaging in 98% of cases for follow-up of ureteric calculi not visible on plain radiograph 4.

Common Pitfalls to Avoid

• Do not rely on bladder distension protocols for detecting ureteric calculi, as stone visualization depends on the imaging modality's inherent sensitivity, not urinary tract opacification 1.
• Avoid using ultrasound alone when clinical suspicion for ureteric calculi is high, as negative ultrasound does not exclude stones—proceed to noncontrast CT 2.
• Be aware that contrast-enhanced CT has slightly lower sensitivity than noncontrast CT for detecting small renal calculi, though stones ≥6 mm are detected with 98% accuracy on contrast studies 1.
• Consider anatomical variants such as duplex collecting systems, which may complicate stone localization even on CT and may require contrast-enhanced imaging for complete anatomical delineation 5.