Primary Orbital Presentation of Mycobacterium chimaera Infection

Mycobacterium chimaera (M. chimaera ) is a slow-growing nontuberculous mycobacterium, which, in humans, is mainly associated with cardiothoracic surgical infections and rarely presents with ocular involvement. This report describes a unique case of orbital infection presenting as an inflammatory mass in a healthy 66-year-old white female, without prior trauma, surgery, or significant medical history. Imaging revealed a diffuse mass, with heterogeneous enhancement, medially in the left orbit, and CT of the trunk revealed mediastinal lymphadenopathy. Histopathology of orbital tissue and mediastinal lymph nodes showed necrotizing granulomatous inflammation, cultures from endobronchial lymph node biopsy isolated M. chimaera , and targeted antimicrobial treatment for nontuberculous mycobacterium resulted in marked clinical improvement. This case highlights the importance of considering atypical infections in the differential diagnosis of orbital inflammatory syndromes.