A Unique Presentation of Chronic Primary Sternal Osteomyelitis With Mediastinal Abscess.

A previously healthy 9-month-old boy presented to the emergency department with 4 days of daily fevers as high as 39.1°C rectally. Parents reported that he was increasingly difficult to console for the previous several days. Although not initially reported, after the diagnosis was made, the parents reported occasional tactile fever and difficulty sleeping, particularly when lying prone, over the preceding few weeks. On examination, the child was febrile (39.2°C rectally) and tachycardic (pulse 140 beats/min). He was alert but crying inconsolably, seemingly in significant discomfort. Complete examinations by multiple physicians failed to demonstrate any apparent source of his pain and fever. Notably, bony tenderness was not appreciated, and he had no erythema or swelling over his sternum. Initial laboratory data demonstrated a white blood cell (WBC) count of 15 900/uL with 53% neutrophils and 5% bands. Erythrocyte sedimentation rate was 20 mm/h and C-reactive protein (CRP) was 22 mg/dL. On admission, cerebrospinal fluid examination, urinalysis, and computed tomography (CT) imaging of the head and abdomen were unremarkable. Chest x-ray demonstrated a retrocardiac left lower lobe infiltrate. He was admitted for further observation and evaluation of fever and irritability. Less than 24 hours after admission, a blood culture was positive for Gram-positive cocci in clusters, later identified as methicillin-susceptible S. aureus (MSSA), and vancomycin was started. Susceptibilities of the isolate demonstrated clindamycin susceptibility and erythromycin resistance. However, the D-test was positive for inducible clindamycin resistance. The isolate additionally demonstrated susceptibility to ciprofloxacin and levofloxacin. Blood cultures continued to be positive for 2 subsequent days. Echocardiogram demonstrated a mediastinal mass possibly mildly compressing the anterior surface of the right ventricle. Of note, the patient slept comfortably during the transthoracic echocardiogram. Chest CT demonstrated a large anterior mediastinal abscess (Figure 1). The abscess tracked around the sternum with marked bony erosion and fragmentation compatible with sternal osteomyelitis. The anterior mediastinal abscess extended from the level of the left brachiocephalic vein to the cardiac apex, and osseous fragments were lying within the abscess (Figure 2). Retrospective review of the chest x-ray revealed destruction of the sternal ossification centers that had not been recognized initially. The cardiovascular surgeons incised and drained the mediastinal abscess, debrided his sternum, and placed a wound vacuum-assisted closure device.