A 12-month-old boy with no significant medical history was transferred from a referring hospital to our facility with 3 days of nasal congestion, dry cough, and fever. His mother reported that the highest temperature measured at home was 37.9°C. The patient was afebrile on initial presentation to the referring hospital, and his examination was notable for clear nasal discharge with a normal respiratory examination result. There was no increased work of breathing and no decreased breath sounds or abnormal lung sounds on examination. The patient was noted to be well appearing, smiling, and interactive. A chest radiograph (CXR) was performed at the referring hospital, which showed a relatively dense opacity in the left upper lobe extending to the apex. Although the pediatric radiologist who read this image noted that the increased density in the left lung apex could represent the thymus, a paraspinal process could not be excluded because of the lack of visualized lung markings (Fig 1). Of note, the opacity also could not be visualized on a lateral view, making the differential between anterior, middle, and posterior pathologies more difficult. Because of this uncertainty, and the varying gravity of mediastinal pathologies, further evaluation with computed tomography (CT) or MRI was recommended. FIGURE 1 Initial anteroposterior CXR (left). Note the opacity in the left upper field. A lateral view (right) is also shown. Note that opacity is not visualized with this view. After discussion with the medical team and the parents, and because of the possibility that additional evaluation with a pediatric hematology-oncology team may be needed, the decision was made to …