Retrosternal density: pulmonary underdevelopment or accessory hemidiaphragm.

Vertical retrosternal density paralleling the sternum, with haziness of a hemithorax on chest roentgenogram, often challenges the clinical acumen of pediatricians, chest physicians, and pediatric radiologists alike. Its presence has been historically linked to either pulmonary underdevelopment and/or accessory hemidiaphragm. The surgical and radiological pediatric literature has long debated this topic, but unfortunately, it has not received much attention in the general pediatric or in pediatric pulmonology literature. The similar radiologic appearance of these two entities can cause confusion both in diagnostic and the therapeutic approach. Many authors advocate an invasive modality, including thoracotomy, as the only definitive way to differentiate between them. We present two similar cases with retrosternal densities, review the pertinent literature, and propose a rational approach to diagnosis and treatment.