D107-23 Empyema Without Borders: A Rare Case of Methicillin-Susceptible Staphylococcus Aureus (MSSA) Empyema Necessitans

Abstract Introduction Empyema necessitans (EN) is a rare but potentially life-threatening complication of untreated empyema, most commonly caused by Mycobacterium tuberculosis or Actinomyces species. We report an exceptionally uncommon case due to methicillin-sensitive Staphylococcus aureus (MSSA), underscoring the importance of timely diagnosis, targeted antimicrobial therapy, and definitive source control. Description A 57-year-old man with diabetes presented with a two-week history of left neck and chest wall swelling, erythema, and pleuritic chest pain. He was afebrile but hypoxic, with leukocytosis. Chest CTA revealed EN with a 98 × 44 mm loculated left pleural effusion extending into the anterior chest wall (98 × 36 mm collection), involving the neck and shoulder soft tissues, and showing erosion of the left costochondral cartilage and clavicular head. Neck CT demonstrated a 77 × 50 mm abscess. Meropenem was initiated, followed by chest tube placement and intrapleural fibrinolytic therapy. Cultures from blood and pleural fluid grew MSSA, prompting a switch to nafcillin. Despite appropriate antibiotic therapy and drainage, blood cultures remained positive for one week until surgical debridement of the neck, chest wall, second rib, and surrounding tissue. Postoperatively, cultures cleared. His hospital course was complicated by hypoxic-hypercapnic respiratory arrest due to mucus plugging and a cardiac arrest following moderate sedation for wound VAC changes. He was subsequently intubated and later discharged to a long-term acute care facility with a tracheostomy because of prolonged ventilator dependence. Discussion EN is characterized by the extension of infection through the parietal pleura into the subcutaneous tissues of the chest wall. Early recognition and intervention are vital to reduce morbidity and mortality, yet diagnosis is often delayed due to the condition’s rarity. Most reported cases are caused by M. tuberculosis (≈70%) or Actinomyces species, whereas S. aureus—particularly MSSA—is an uncommon pathogen. To our knowledge, this represents only the third documented case of MSSA-associated EN in an adult. Our patient was treated with chest tube drainage, intrapleural fibrinolytic therapy, targeted antibiotics, and surgical debridement of infected tissue. Notably, blood cultures remained persistently positive despite appropriate antimicrobial therapy and thoracostomy, clearing only after surgical intervention—underscoring the critical importance of early and complete source control in the management of EN. Given its potential for rapid progression and high morbidity, EN demands a high index of suspicion, organism-specific treatment, and early multidisciplinary intervention to optimize patient outcomes. This abstract is funded by: None