Matchbox sign

Okay kiddo, have you ever seen a matchbox? You know, the little box where we keep matches to light candles, stoves or fireplaces? Well, sometimes doctors use the term "matchbox sign" to describe something they see on an X-ray or an ultrasound image.

When someone breathes, their lungs inflate and deflate, like a balloon. But sometimes, the area between the lungs and the chest wall gets filled with air or other things like fluid or blood. When this happens, the lungs can't expand properly and the person may have trouble breathing.

The matchbox sign is when doctors can see on an image that the distance between the ribs and the lungs is very small, almost like a matchbox. This tells the doctor that the lungs are being squished by something outside of them. It's not a good thing, but it helps the doctor diagnose and treat the problem so the person can breathe better.