Croup vs Epiglottitis
- Both are sick, stridor-y kids — but croup narrows the windpipe below the cords, and epiglottitis swells the flap above them.
- Croup's X-ray sign is the steeple sign: the airway tapers to a pointy church-spire shape on the frontal neck film.
- Epiglottitis's X-ray sign is the thumbprint sign: a fat, round epiglottis on the lateral neck film.
- Croup is common, viral, and usually self-limited. Epiglottitis is the rare, life-threatening one — a true "don't miss."
- If you genuinely suspect epiglottitis, the airway comes first. Do not send the kid off to a quiet X-ray room to maybe die alone.
Two little kids show up wheezing and barking, both making that scary high-pitched noise on breathing in (that's stridor — the sound of air squeezing through a too-narrow pipe). They can look almost identical at the door. The whole game is figuring out where the pipe is pinched, because the answer changes everything from "go home with a humidifier" to "call anesthesia now."
The trick that makes this stick: think of the airway like a drinking straw with a little hinged lid at the top. Croup pinches the straw itself, just below the lid. Epiglottitis swells up the lid.
Croup: the straw gets pinched
Croup (the fancy name is laryngotracheobronchitis, which is just "inflammation of the voice box, windpipe, and bronchi" wearing a tuxedo) is a viral infection that makes the airway swell just below the vocal cords — the subglottic region. That spot is the narrowest part of a small child's airway to begin with, so a little swelling goes a long way. The classic patient is a toddler with a barky, seal-like cough who got worse overnight.
Here's the honest part: croup is usually a clinical diagnosis, and most kids never need a film at all. But when we do get a frontal (AP) neck radiograph, the swollen subglottic airway loses its normal squared-off shoulders and tapers to a narrow point — like the spire on top of a church.
The steeple sign is helpful when present but it's neither perfectly sensitive nor specific — plenty of croupy kids have a normal-looking film, and the diagnosis is still made at the bedside. A normal X-ray does not rule croup out.
Epiglottitis: the lid swells shut
Now the scary sibling. Epiglottitis is swelling of the epiglottis — that little flap that folds down over your airway when you swallow so your sandwich goes to your stomach instead of your lungs. Infect and inflame that flap and it balloons up above the cords (the supraglottic region), threatening to flop down and seal the airway entirely.
The classic picture is a child who looks genuinely toxic: high fever, drooling (swallowing hurts too much), muffled "hot potato" voice, and sitting bolt upright leaning forward in the tripod position — instinctively holding the airway open. Thanks to the Hib vaccine this has become uncommon in kids, but it absolutely still happens, and it shows up in adults too.
On the lateral neck radiograph, the normally thin, curved epiglottis swells into a fat, rounded blob at the base of the tongue — the thumbprint sign, because it looks like someone pressed a thumb into the airway.
If you truly suspect epiglottitis, securing the airway comes before any imaging. Agitating a child with a critical airway — laying them flat, forcing an unwanted X-ray, poking at the throat — can trigger complete obstruction. The right move is a calm, controlled trip to the OR with people who can intubate. The film is a luxury you only get if the airway is stable.
Telling them apart at a glance
Same noise, different floor of the airway. Here's the side-by-side:
| Feature | Croup | Epiglottitis |
|---|---|---|
| What's swollen | Subglottic windpipe (the straw) | Epiglottis (the lid) |
| Cause | Usually viral | Bacterial |
| Typical look | Barky cough, gradual, "uncomfortable" | Drooling, toxic, tripoding, "I am dying" |
| Best X-ray view | Frontal (AP) neck | Lateral neck |
| The sign | Steeple sign | Thumbprint sign |
| Vibe | Common, usually self-limited | Rare, true emergency |
Don't let a normal-looking neck film talk you out of a sick kid. Both signs can be subtle or absent, and a poorly positioned or rotated pediatric neck film fakes pseudothickening all the time. The child in front of you outranks the picture — if they look like epiglottitis, treat the airway, not the radiograph.
The one thing to walk away with
Stridor tells you the pipe is narrow; your job is to localize above or below the cords. Below the cords, tapering to a spire = croup. Above the cords, a fat thumbprint epiglottis = epiglottitis, and that's the one where you protect the airway before you reach for the camera. While you're in the pediatric airway, it's worth knowing its loud cousin — the sudden, unilateral wheeze of an inhaled foreign body — which can mimic this whole scene.