Clinical scenario
A 62-year-old man with a history of kidney stones and hypertension presents with acute right-sided flank pain radiating to the groin, with nausea and vomiting. Vital signs are stable. A bedside renal ultrasound is performed.
Review the accompanying video clip below.
What does the image show?
Color Doppler shows a classic twinkle artifact at the ureterovesical junction (UVJ). The arrow marks an echogenic stone at the UVJ, with the twinkle artifact on color Doppler.
What is the twinkle artifact?
The twinkle artifact is a rapidly alternating color signal immediately behind a stationary, strongly reflective object, which falsely suggests motion. Behind an echogenic focus in the urinary tract, it suggests a stone. Here, it marks a stone at the UVJ.
Is it useful?
Yes. The twinkle artifact increases sensitivity for detecting small or poorly visualized stones.
Does this patient need a CT?
CT remains the gold standard for nephrolithiasis. In stable patients, however, ultrasound with a twinkle artifact can often confirm the diagnosis.
Can flank pain be managed without a CT every time?
Yes, and this has been studied. In a multicenter randomized trial of ED patients with suspected nephrolithiasis, initial ultrasonography was associated with lower cumulative radiation exposure than initial CT, with no significant differences in high-risk diagnoses with complications, serious adverse events, pain scores, return ED visits, or hospitalizations (Smith-Bindman 2014).
Management in this case
Pain control, hydration, and outpatient urology follow-up. Most distal stones pass spontaneously.
Clinical pearls
Turn on color Doppler over a suspected stone. Twinkle can reveal stones that do not shadow well.
In stable patients with a typical presentation, an ultrasound-first strategy is supported by trial evidence.
Get CT when the diagnosis is uncertain, the patient is unstable or febrile with obstruction, or an alternative diagnosis is a concern.
References
Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014;371:1100–1110. doi:10.1056/NEJMoa1404446
