Radiographic evaluation of foreign body aspiration is helpful, but a normal radiographic examination does not exclude the possibility of an airway foreign body. Various series have reported normal radiographs in 6 to 80% of children with proven foreign bodies in the tracheobronchial tree. Although some foreign bodies are easily seen on standard chest radiographs (Figure 36-1), 80 to 90% of aspirated foreign bodies are vegetative material, thus radiolucent and not visualized. The most common abnormal finding in the pediatric patient with aspiration is hyperexpansion of the affected side, which occurs in approximately 60% of cases (Figure 36-2), although atelectasis or an infiltrate may be noted in a lesser number of cases. In the adult population, atelectasis and loss of lung volume is more common on the affected side (Figure 36-3). Not unexpectedly, the more dangerous laryngotracheal foreign bodies are likely to have normal x-rays. However, this subset of patients, usually accounting for 5 to 15% of all foreign body aspirations, is more likely to present with severe clinical symptoms (dyspnea, sternal retraction, cyanosis). If there is a significant delay in presentation, as occurs in up to 50% of cases of foreign body aspiration in the pediatric age group, then there is higher likelihood that the initial chest x-rays will be abnormal as secondary features become apparent in the obstructed lung.
If the chest radiographs are normal, then inspiratory and expiratory films or films in both the left and right lateral decubitus positions may be helpful. In a child with partial bronchial obstruction, the expiratory film will demonstrate hyperinflation secondary to check-valve effect from the obstructing foreign body (Figures 36-4A-C). Some authors promote the expiratory phase by placing gentle pressure over the child's epigastrium and timing exposure of the film with a natural expiration. Even with these measures, due to an inability to cooperate, inspiratory and expiratory films in most young pediatric patients are inconclusive. In the younger patient, the use of right and left lateral decubitus views of the chest may be helpful. The lung in the dependent position would typically appear compacted. In a child with a foreign body aspiration and partial obstruction, the dependent lung would not appear compressed and may even appear slightly hyperinflated.
False-positive findings on a chest radiograph will occur in about 12% of children who are not found to have an aspirated foreign body on tracheobronchoscopy. Conversely, up to 65% of the children who had normal chest x-rays, but a history consistent with aspiration, were found to have a foreign body on endoscopy.15
In an older patient, fluoroscopy of the chest may be helpful in establishing the diagnosis of aspirated foreign body. With laryngotracheal foreign bodies, paradoxical mediastinal movement and an increase in the size of the mediastinal structures may be noted during inspiration. However, abnormal fluoroscopic findings are less frequently seen with bronchial foreign bodies.17 Occasionally, with foreign bodies in a bronchial location, a shift of the mediastinal structures toward the normal airway may be noted during expiration, because of the check-valve effect of the partially obstructing lesion and entrapment of air in the obstructed lung.
Although authors have reported the use of ventilation-perfusion scanning, it is infrequently used in the emergent evaluation of a possible foreign body obstruction. Similarly, computed tomography (CT) scans have been reported to be helpful, particularly in a patient who may have a delayed presentation and an atypical history. However, findings on CT imaging usually show the secondary effects of the foreign body aspiration (Figure 36-5) and may or may not demonstrate the foreign body itself.18 In the acute setting, there appears to be little role for this imaging study.
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