A peril of minimally invasive surgery

A 23-YEAR-OLD woman presented with rheumatic mitral valve stenosis and regurgitation. She underwent a valvular commissurotomy and annuloplasty through a minimally invasive median sternotomy. Her operative course was unremarkable. However, after arrival in the intensive care unit, a postoperative chest radiograph showed an abnormality that required the patient to return to the operating room for rnediastinal reexploration. Identify the abnormality seen on the chest radiograph (Fig 1).