Radiopathological Features and Identification of Mycobacterial Infections in Granulomatous Nodules Resected from the Lung.

BACKGROUND: Pulmonary granulomas are sometimes resected because they resemble lung cancer and false-positive findings come through from positron emission tomography (PET) using 18fluorine-fluorodeoxyglucose (18F-FDG). Mycobacterial infection is a common cause of granulomas. OBJECTIVE: The purpose of this study was to evaluate the radiopathological features and the methods for identifying mycobacterial infections in granulomatous nodules resected from the lung. METHODS: Thirty-five solitary lesions resected because of suspected lung cancer were enrolled, including 22 nonfungal granulomatous lesions and 13 benign lesions as controls. The radiological, microbiological, and histological findings were reviewed. To identify mycobacterial infection, immunohistochemical (IHC) staining, IS6110 polymerase chain reaction (PCR), and real-time PCR for the detection of Mycobacterium tuberculosis (TB) were performed using formalin-fixed and paraffin-embedded tissue specimens. The correlations between the radiopathological features and the median maximum standardized uptake value (SUVmax) of 18F-FDG PET were also evaluated. RESULTS: Mycobacteria were isolated from the cultures of 10 of the granulomatous lesions, including TB from 2 and Mycobacterium avium complex from 8. The mean size of the nodules in the culture-positive group was significantly larger than that of those in the culture-negative group (30.5 ± 13.1 vs. 15.1 ± 6.3 mm, p = 0.003). IHC stainings were positive in 15 granulomas. Eight granulomas were positive in IS6110 PCR, and 7 of them were also positive in real-time PCR. SUVmax was ≥2.5 in all of the PCR-positive granulomas. CONCLUSION: The most frequent cause of granulomatous lesions was mycobacterial infection. It seemed that the culture result was associated with nodule size and that the results of IS6110 were associated with 18F-FDG-uptake.