Twinkle is a colour Doppler artefact behind a strongly reflecting, rough surface. It looks like a rapidly flickering red and blue tail, although nothing behind the target is moving. It can make a small stone easier to spot, but on its own it is not specific enough to be the diagnosis: in some studies around half of twinkling spots were not stones on CT.
Scan images in the graphic are fabricated educational illustrations, not patient scans.
The scan
- Scan the kidney in long axis and transverse on greyscale first.
- Look for a bright focus with a clean shadow behind it.
- Put a small colour box over it. Lower the colour scale enough to show twinkle without filling the kidney with noise.
- Hold the probe still. A real twinkle tail stays anchored to the bright focus.
- Look for obstruction: a dilated collecting system or ureter, and, where it helps, asymmetry of the ureteric jets in the bladder.
Reading the clue
- More convincing: a bright focus, a clean shadow and an anchored twinkle in a place a stone can sit.
- Less convincing: twinkle with no matching focus, no shadow and no obstruction.
- Calcified vessels, calcification in the kidney tissue, strong interfaces and machine noise can twinkle too.
Action
Put the finding together with the symptoms, urine dip, kidney function, infection risk and the need for definitive imaging. Fever with an obstructed kidney is an emergency.
