Bacterial Granulomatous Lung Diseases: Radiological Findings and Differential Diagnosis

Background Granulomatous lung diseases include a spectrum of disorders, both infectious and noninfectious, unified by the presence of granulomas in the lung parenchyma. Granulomas are microscopic, organized collections of immune cells that arise as a response to persistent antigenic stimulation. Infectious granulomatous lung diseases arise from a variety of microbial agents, that include most frequently Mycobacterium tuberculosis, non-tuberculous mycobacteria, Nocardia, and Borrelia, as well as a wide range of fungal pathogens including Histoplasma, Cryptococcus, Pneumocystis, and Aspergillus species. Methods and Results: Definitive diagnosis is achieved through direct identification and subsequent culture of the causative pathogen in appropriate clinical specimens, including sputum, bronchoscopic samples, gastric aspirates, or pleural fluid. Imaging is fundamental for the detection and characterization of pulmonary granulomas. HRCT allows precise assessment of the number, size, and distribution of granulomatous lesions, can suggest an infectious etiology based on specific imaging patterns, and is essential for monitoring response to therapy over time. Differential diagnosis is challenging due to the numerous different imaging appearances with whom granulomatous lung diseases may manifest. Conclusions: The purpose of our review is to describe the spectrum of infectious granulomatous lung diseases caused by bacterial pathogens, highlighting their diverse radiologic presentations in order to assist radiologists in recognizing these entities and improving diagnostic accuracy.