Sternal wound infection is a known complication of coronary artery bypass graft, which occurs in approximately 1-2% of sternotomies. The wound infection can be a limited superficial infection, or may progress to mediastinitis.
Clinically, patients with mediastinitis are more likely to have systemic symptoms of fever and leukocytosis. Wound infections are usually monomicrobial. The most common organism is methicillin sensitive staphylococcus aureus (MSSA), followed by methicillin resistant staph (MRSA). MSSA is usually related to preoperative colonization, whereas MRSA is usually a nosocomial infection.
The earliest finding is sternal dehiscence, and there may be disruption or alteration of the appearance of the cerclage wires. Gaps greater than 3 mm are usually indicative of sternal instability, and progressive widening indicates dehiscence. Dehiscence is frequently associaetd with infection, and this finding should raise possibility of infection. Infection will usually manifest approximately 2 weeks postoperatively. If the infection spreads to osteomyelitis of the bone, CT will show osseous erosion, Mediastinitis will show fluid collections and mediastinal gas. The distinctions are important because mortality is increased in mediastinitis compared to superficial wound infections. Additionally, the imaging findings may direct the provider to specific treatments.