Croup is a viral infection common in young children that leads to swelling in the upper airway. This inflammation affects the voice box (larynx) and windpipe (trachea), causing a distinctive “barking” cough. Children with croup also develop hoarseness and a high-pitched, noisy sound called stridor when they inhale. The condition begins with common cold symptoms, and a diagnosis is made based on a clinical evaluation during a physical exam.
The Role of X-Rays in Croup Diagnosis
In most instances, a physician diagnoses croup without imaging tests, as the characteristic cough and breathing sounds are sufficient for a diagnosis. An X-ray is reserved for cases where the clinical picture is unclear or more severe. For example, a neck X-ray may be ordered if a child’s symptoms are atypical, if they have significant respiratory distress, or if they do not respond to standard treatments. This helps ensure the symptoms are not caused by a different condition.
Identifying the Steeple Sign
When an X-ray of the neck is performed, clinicians may look for a specific finding known as the steeple sign, visible on a front-view, or anteroposterior (AP), X-ray. It is named for its resemblance to the tapering point of a church steeple. The steeple shape is created by the swelling and narrowing of the airway just below the vocal cords, a region called the subglottic trachea. This narrowing appears as a symmetric, cone-like shape on the X-ray image.
The steeple sign is a classic indicator, but its presence is not guaranteed in every case. The absence of this sign does not rule out a croup diagnosis, so a physician integrates imaging results with the child’s physical symptoms.
Ruling Out Other Conditions
An X-ray of the neck or chest is a tool for differential diagnosis, helping physicians distinguish croup from other conditions with similar symptoms. This is important when a child presents with significant breathing difficulty, as treatment can vary. The imaging helps to exclude other potential reasons for airway obstruction.
One serious condition that can mimic croup is epiglottitis, a bacterial infection causing swelling of the epiglottis. On a lateral, or side-view, X-ray, epiglottitis can produce a “thumb sign,” which looks different from the steeple sign.
Another possibility an X-ray can identify is an inhaled foreign body. If an object is lodged in the airway, it can cause symptoms like coughing and noisy breathing that might be confused with an infection. An X-ray can visualize the object, confirming its presence and location.