Chest X-Ray for HPIV Chest x-ray is important when it is difficult to derive a diagnosis especially when epiglottitis, retropharyngeal abscess and foreign body aspiration are the possible diagnoses. Anteroposterior views of neck of patients who present with croup reveal the class steeple sign. Steeple sign is the narrowing of air shadow of trachea associated with subepiglottic swelling. Lateral views of neck of patients who present with epiglottitis reveal enlarged epiglottis and ballooning of hypopharynx.