[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Radiology](https://durgical.com/en/radiology/) › [Chest](https://durgical.com/en/radiology/areas/chest/) › The child's chest X-ray: thymus, foreign body, croup and epiglottitis # The child's chest X-ray: thymus, foreign body, croup and epiglottitis - Finding A child's X-ray has its own normal: a big thymus near the heart. It also helps when a child chokes on something or has noisy breathing. Updated Nov 13, 2026 ## Key points - Big smooth thymus in infants is normal; it does not push the trachea. - Steeple sign = croup (AP neck); thumb sign = epiglottitis (lateral neck). - Epiglottitis: airway first, no X-ray or throat exam. - Foreign body: look for air trapping; a normal film does not exclude it. ## What it is A child's chest is not a small adult's. In infants the thymus is large and may fill the upper anterior mediastinum, looking like a mass, and the heart looks relatively large on AP films. Imaging is used less and with care: croup is a clinical diagnosis and needs no X-ray in a typical case, and a child with suspected epiglottitis must not be sent for X-ray before the airway is safe. In foreign-body aspiration most objects are not radio-opaque, so the film shows the effect rather than the object: one lung that stays inflated when it should empty. When the story is strong, a normal X-ray does not exclude a foreign body. ## What it looks like - Normal thymus: a smooth soft-tissue shadow in the upper anterior mediastinum, often triangular like a sail, with a wavy edge where the ribs press on it; it does not compress the trachea. - The thymus is largest relative to the chest in infancy and becomes less visible through early childhood. - Croup: on the AP neck view the subglottic airway narrows into a pointed, steeple-like shape. - Epiglottitis: on the lateral neck view the epiglottis is swollen and rounded like a thumb, with thick aryepiglottic folds. - Aspirated foreign body: the affected lung stays hyperlucent and does not lose volume on expiration, and the mediastinum shifts away from it. - Round metal object in the oesophagus: seen face-on as a disc on the AP view. A button battery shows a double ring and is an emergency. ## Why it looks that way - A foreign body in a bronchus can act as a one-way valve: air enters on inspiration but cannot leave, so that lung stays big and dark. - The thymus is soft and moulds around neighbouring structures, so it does not displace the airway or vessels. - Viral inflammation in croup swells the subglottis, the narrowest part of the child's airway; in epiglottitis the swelling is above, at the epiglottis. ## Differential and pitfalls - A large normal thymus is often mistaken for a mass or cardiomegaly; a mass compresses or displaces the trachea, the thymus does not. - Most foreign bodies (nuts, food) are radiolucent: the X-ray is often normal, especially soon after the event. - Children who cannot follow breathing commands: lateral decubitus views; the side lying down should lose volume, and a lung that stays inflated suggests air trapping. - Examining the throat or lying a child with suspected epiglottitis flat can trigger complete obstruction. - A coin seen edge-on on the AP view suggests it is in the trachea rather than the oesophagus; confirm with the lateral view. ## Next step - Suspected epiglottitis: keep the child calm and upright, no X-ray or throat exam; call anaesthesia and ENT to secure the airway. - Typical croup: no imaging; X-ray only if the course is atypical, severe or not improving. - Strong story of choking: rigid bronchoscopy even if the X-ray is normal; discuss with paediatric surgery or ENT. - Swallowed object: X-ray from neck to abdomen; a button battery in the oesophagus needs urgent removal. - Mediastinal shadow that compresses the trachea or looks unusual: ultrasound of the thymus or discuss with the paediatric radiologist before a CT. ## Test yourself Think of the answer, then tap the question to see it. ## How do you tell a normal thymus from a mediastinal mass in an infant? The thymus is smooth, may have a sail shape or wavy edge and does not compress or displace the trachea or vessels; a mass does. ## What is the steeple sign and what does it suggest? Narrowing of the subglottic airway into a pointed shape on the AP neck X-ray; it suggests croup, which is still diagnosed clinically. ## Why can the chest X-ray be normal after foreign-body aspiration? Most aspirated objects such as food and nuts are radiolucent, and air trapping may be absent early; a strong history still needs bronchoscopy. ## What does the affected lung do on an expiratory film when a foreign body blocks its bronchus? It stays inflated and dark (air trapping) instead of losing volume, and the mediastinum shifts toward the other side. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/radiology/the-child-s-chest-x-ray-thymus-foreign-body-croup-and-epiglottitis/) ## Elsewhere in DurgiPedia - [Bronchial obstruction syndrome](https://durgical.com/en/clinical-exam/bronchial-obstruction-syndrome/) - [Vital signs in children: how they change with age](https://durgical.com/en/clinical-exam/vital-signs-in-children-how-they-change-with-age/) ## Connections ## Related 6 - [Imaging children: less radiation, more ultrasound](https://durgical.com/en/radiology/imaging-children-less-radiation-more-ultrasound/) - [Reading a chest X-ray step by step](https://durgical.com/en/radiology/reading-a-chest-x-ray-step-by-step/) - [Is this chest X-ray good enough? Projection, rotation, inspiration and exposure](https://durgical.com/en/radiology/is-this-chest-x-ray-good-enough-projection-rotation-inspiration-and-exposure/) - [The widened mediastinum and the hila](https://durgical.com/en/radiology/the-widened-mediastinum-and-the-hila/) - [Free air in the chest: pneumomediastinum and subcutaneous emphysema](https://durgical.com/en/radiology/free-air-in-the-chest-pneumomediastinum-and-subcutaneous-emphysema/) - [Radiation in medical imaging: risk, ALARA and pregnancy](https://durgical.com/en/radiology/radiation-in-medical-imaging-risk-alara-and-pregnancy/) ## Related conditions 4 - [Croup (laryngotracheobronchitis)](https://durgical.com/en/conditions/croup/) - [Acute epiglottitis](https://durgical.com/en/conditions/acute-epiglottitis/) - [Foreign body aspiration in children](https://durgical.com/en/conditions/foreign-body-aspiration-in-children/) - [Foreign-body airway obstruction (choking)](https://durgical.com/en/conditions/foreign-body-airway-obstruction/) [← All of radiology](https://durgical.com/en/radiology/) Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols. Sources: [Croup](https://www.ncbi.nlm.nih.gov/books/NBK431070/) (StatPearls (NCBI Bookshelf), 2025); [Epiglottitis](https://www.ncbi.nlm.nih.gov/books/NBK430960/) (StatPearls (NCBI Bookshelf), 2024); [Foreign Body Airway Obstruction](https://www.ncbi.nlm.nih.gov/books/NBK553186/) (StatPearls (NCBI Bookshelf), 2024); [Anatomy, Head and Neck, Thymus](https://www.ncbi.nlm.nih.gov/books/NBK539748/) (StatPearls (NCBI Bookshelf), 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/radiology/the-child-s-chest-x-ray-thymus-foreign-body-croup-and-epiglottitis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/radiology/the-child-s-chest-x-ray-thymus-foreign-body-croup-and-epiglottitis/