Which statement about expiratory films in suspected foreign body aspiration is true?

• A. They are never helpful
• B. They can reveal air trapping even if inspiration films are normal
• C. They always show the foreign body
• D. They are contraindicated in children

Answer: (B)

Expiratory radiographs can reveal air trapping from partial airway obstruction caused by a suspected foreign body, even when the inspiratory view looks normal. When a foreign body acts like a check valve, air can enter the lung on inspiration but cannot escape fully on expiration. That leads to unilateral or focal hyperinflation on the expiratory film, sometimes with diaphragmatic flattening or mediastinal shift if the extent is substantial. Because many swallowed objects are radiolucent, this secondary sign on expiration is often the key clue pointing toward foreign body aspiration and guiding further evaluation, such as bronchoscopy. Expiratory views are not universal proof of a foreign body, but they provide important diagnostic information when inspiration films are unrevealing. They aren’t contraindicated; they’re simply dependent on the child’s ability to cooperate and on careful technique to obtain a true expiratory view.