FB aspiration is easily confused with more common causes of upper respiratory diseases because 36% of patients have fever, 35% have wheezes, and 38% have rales. Plain chest radiographs can be normal in > 50% of tracheal FB and 25% of bronchial FB; more than 75% of FB in children < 3 years of age are radiolucent. In cases of complete obstruction, atelectasis may be found. In partial obstructions, a ball valve effect occurs, with air trapping caused by the FB leading to hyperinflation of the obstructed lung. Thus, in a stable cooperative child, inspiratory and expiratory posteroanterior chest radiographs may be helpful. In a stable but noncooperative child, decubitus films may be used but are less sensitive than fluoroscopy. FB aspiration is definitively diagnosed preoperatively in only one-third of cases; thus, if clinically suspected, laryngoscopy is indicated.
Upper esophageal FB are usually radiopaque and can impinge on the posterior aspect of the trachea. Patients may present with stridor, and typically have dysphagia. Radiographically, flat FBs such as coins are usually oriented in the sagittal plane when located in the trachea (which appear as a thick line in an anterioposterior chest radiograph) and in the coronal plane when in the esophagus (which appear round on an anterioposterior chest radiograph).