A 59-year-old diabetic male presents to the emergency department complaining of worsening dyspnea 5 weeks after sustaining a fractured sternum in a motor vehicle collision. Initial noncontrast CT (a) demonstrates a gas-containing collection at the site of the sternal fracture and a bone fragment projecting posteriorly (arrow). CECT ((b) sagittal and (c) axial) shows pericardial hyperenhancement and effusion. Mediastinal gas is present (arrowheads). Separate aspirations of the sternal collection and pericardial fluid both yielded pus which grew methicillin-sensitive Staph. aureus. Broad-spectrum antibiotic therapy was begun and a pericardial window was placed.