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

Abstract

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 (SUV_max) 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. SUV_max 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.

Granulomatous Nodules: Know the Ropes

“…Morphologically, caseating and noncaseating granulomatous reactions can occur, which often do not allow a differentiation between various infectious etiologies and hypersensitivity reactions. Regarding the Ziehl-Neelsen stain, an important point to remember is that, in most cases, mycobacteria are few and difficult to find, a fact also described by Sakakibara et al [6] (Ziehl-Neelsen staining was positive in only 3 cases [14%], although 16 [73%] of the nodules had caseous necrosis). It is not uncommon to examine several Solitary pulmonary nodules (SPNs) are commonly encountered in clinical practice, and the management involves a wide variety of dilemma, from the imaging method to be applied to the invasive approach used for the diagnosis and treatment.…”

“…It is accepted that the spectrum of mycobacterial infections is multifaceted, from the death of the organism to latent or active infection. Differences obtained between the cultures and immunohistochemical staining results and the association of the culture result with the nodule size in the report by Sakakibara et al [6] highlight the fact that there is an unmet need for large studies that will allow us to better define the role and value of mycobacteria status within the granuloma.…”

“…A study of 279 patients in the large necrotizing granulomas but find only a few mycobacteria. AFB culture was diagnostic of nearly half of the studied granuloma cases, while immunohistochemical staining had the highest sensitivity [6] .…”

“…In a recent issue of Respiration , Sakakibara et al [6] evaluated the radiopathologic features of mycobacterial infections in granulomas suspected to be lung cancers, the methods used to identify the infections, and the correlations with SUVmax.…”

“…Even after a thorough review of clinical information, histologic, and bacteriological tests, 14% of the pulmonary granulomas remained unexplained [6] . Similar cases have previously been reported by Ulbright and Katzenstein [7] .…”