Bronchocentric Granulomatosis Mimicking Diffuse Malignancy: Reticulonodular Lung Disease With Widespread 2-Deoxy-2-[¹⁸F]fluoro-D-Glucose Uptake

Bronchocentric granulomatosis (BCG) is a rare airway-centered granulomatous disorder and is regarded as an immunologically mediated reaction rather than an active infectious process. Its imaging findings are heterogeneous and often non-specific, frequently mimicking malignant or infectious lung diseases. We report a 63-year-old woman who presented with persistent fever and diffuse bilateral reticulonodular opacities on chest computed tomography (CT), an uncommon imaging manifestation of BCG. 2-Deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography/CT ([¹⁸F]FDG-PET/CT) demonstrated diffuse pulmonary uptake without extrapulmonary involvement, raising concern for malignant disease. Repeated bronchoscopic biopsies were non-diagnostic, and a surgical lung biopsy revealed bronchocentric granulomatous inflammation with only minimal fungal elements, leading to a diagnosis of BCG. Diffuse reticulonodular CT patterns and [¹⁸F]FDG-PET findings in BCG have been rarely reported. This case highlights that BCG can present with metabolically active diffuse lung disease and be mistaken for malignancy. Awareness of this rare entity and its atypical imaging features is important for radiologists when interpreting diffuse nodular lung disease with inconclusive microbiological results.