B73-51 A Fungal Foundation, a Bacterial Build-up: Unraveling Complex Mediastinal Infection in a 41-Year-Old Male

Abstract Mediastinal masses frequently blur infectious, inflammatory, and malignant etiologies. Endemic mycoses, particularly Histoplasma capsulatum, can produce mediastinal granulomas resembling neoplasia. We report a mixed fungal-bacterial mediastinal process closely mimicking malignancy. This case describes a 41-year-old incarcerated male with Wolff-Parkinson-White syndrome, gastroesophageal reflux disease, gastric sleeve, and hypertension presented with one month of fever, pleuritic chest pain, exertional dyspnea, unintentional 30lb weight loss, and recent travel to the Dominican Republic, Mexico, Peru, Ohio, and Honduras. Physical exam noted tachycardia and fever but was otherwise unremarkable. Laboratory studies revealed leukocytosis, anemia, marked thrombocytosis, hypoalbuminemia, and elevated ESR and CRP. HIV and tuberculosis testing were negative; Histoplasma antibodies were detected (1:8). Contrastenhanced CT revealed a large irregular posterior mediastinal mass with coarse calcifications and air locules, inseparable from the distal esophagus, with right hilar (2.0 × 1.6 cm) and right paratracheal (1.7 × 1.4 cm) adenopathy, small bilateral effusions, and basal atelectasis. Esophagram excluded perforation. Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) of the enlarged subcarinal (station 7) lymph node yielded purulent material. Cytology was benign. Gram stain showed white blood cells and streptococci; culture grew Streptococcus viridans and Staphylococcus epidermidis. Cefepime and metronidazole were initiated, and itraconazole was added with a planned six-month course. Two weeks later, CT chest/abdomen/pelvis demonstrated decreased size of the mediastinal mass and adenopathy with resolution of intralesional air, effusions, and atelectasis. Differentiating infectious from neoplastic mediastinal disease remains challenging, particularly in endemic regions. Calcifications suggesting granulomatous disease and cough due to airway inflammation may favor benign etiologies, though most findings are nonspecific. In this patient, systemic inflammation, constitutional symptoms, and a complex mediastinal mass initially raised concern for malignancy with possible esophageal perforation. However, a low-titer Histoplasma antibody and imaging calcifications, along with a purulent lymph node aspirate growing Streptococcus viridans, supported bacterial lymphadenitis superimposed on Histoplasma-related granulomatous infection. The coexistence of Histoplasma-associated mediastinal granuloma with abscess can closely mimic malignancy or esophageal perforation, particularly when intralesional air is present. This case underscores the importance of integrating imaging, microbiologic, and cytologic findings to accurately achieve an accurate diagnosis in complex mediastinal disease in endemic areas. In endemic settings, a posterior mediastinal mass with air locules and adenopathy may represent Histoplasmarelated granulomatous disease complicated by abscess. Early EBUSTBNA with microbiologic and cytologic sampling allows effective antifungal and antibacterial treatment, preventing unnecessary oncologic workups and invasive surgery. This abstract is funded by: None