Deep Chest Wall Abscess Involving the Pectoralis Muscle Caused by Actinomyces turicensis and Bacteroides ovatus Mimicking Necrotizing Soft Tissue Infection.

Deep chest wall abscesses may be difficult to distinguish from primary pyomyositis and necrotizing soft-tissue infection because of overlapping clinical and radiographic findings. Although soft-tissue gas raises concern for necrotizing infection, it is not independently diagnostic and may reflect anaerobic bacterial activity, communication with the skin, or prior instrumentation. Infections of the pectoral region involving uncommon polymicrobial organisms are rarely reported. A 61-year-old man with prediabetes, hypertension, chronic kidney disease, and a prior cerebrovascular accident presented with a progressively worsening left anterior chest wall lesion after incomplete outpatient incision and drainage and a partial course of cephalexin. Computed tomography demonstrated a 7.0 × 4.1 × 2.2 cm gas-containing collection within the left upper anterior chest wall that abutted the pectoralis musculature, with associated muscular edema. These findings raised concern for necrotizing soft-tissue infection and prompted broad-spectrum antimicrobial therapy and urgent surgical evaluation. Initial bedside incision and drainage yielded copious purulent material. Persistent induration and loculations required repeat exploration, creation of a second incision, and placement of a Penrose drain. Cultures of material obtained directly from the abscess cavity grew Actinomyces turicensis and Bacteroides ovatus. Antimicrobial therapy was subsequently changed to intravenous ampicillin-sulbactam followed by oral amoxicillin-clavulanate. The patient improved following additional source control and culture-directed therapy, without evidence of fascial necrosis or a need for extensive debridement. At two-week follow-up, purulent drainage had resolved, and the Penrose drain was removed without complication. This case describes an unusual gas-containing deep chest wall abscess involving the pectoral region with secondary muscular inflammation. It demonstrates the importance of distinguishing primary intramuscular infection from contiguous involvement by an adjacent abscess and recognizing that soft-tissue gas alone does not establish necrotizing infection. Prompt surgical assessment, adequate source control, appropriately obtained cultures, and integration of clinical, imaging, operative, and microbiologic findings are essential to guide management.