PURPOSE: To describe the microbiologic and radiologic features of patients with surgically proven infectious granulomas initially presenting as indeterminate SPN's.
METHODS: We conducted a retrospective review of 29 cases of infectious SPN's surgically resected from January 2001 to December 2005 at our institution. Subjects were identified based on combined ICD-9 codes for lung resection with an associated infectious diagnosis, limiting our search to SPN's with histopathology consistent with infection and/or to those with positive lung cultures. Only nodules ≤;3 cm on chest CT without associated atelectasis, consolidation or effusion were included.
RESULTS: The patient population consisted of 52% males and 48% females, mean age of 55 years. By histopathology, fungal agents were identified by Gomori-Methenamine Silver stain and classified into: Histoplasma (55%), Cryptococcus (10%), and Coccidiodes (7%). Ziehl-Neelsen stain was positive for acid fast bacilli (AFB) in 3 (10%), not further identified due to negative AFB cultures. The pathogen in 3 other cases, negative on histopathology but AFB culture positive, was identified as Mycobacterium avium complex by DNA gene probe. The remaining 2 out of 29 consisted of necrotizing granulomas negative on stain and culture, but clinically consistent with infection. Among the fungal nodules, 16 of 22 showed active inflammation while the remaining 6 had inactive fibrocaseous granulomas. Tissue fungal and AFB cultures were positive in 27% and 50% of fungal and mycobacterial nodules respectively. In addition, 23 of 29 patients underwent fluoro-18-deoxyglucose positron emission (FDG-PET), with 77% of fungal and 100% of mycobacterial nodules positive for increased uptake (standardized uptake value (SUV) of ≥2.5). Mean SUV was 5.3.
CONCLUSION: The infectious etiologies in our series of patients primarily included yeast forms and mycobacteria. In addition, a majority of these SPN's had positive FDG-PET scans which could be a reflection of the associated high proportion of nodules with active inflammation on pathology.
CLINICAL IMPLICATIONS: The differential diagnoses for resected infectious SPN's essentially include yeast organisms and mycobacteria. That these nodules are FDG-avid clearly makes the preoperative evaluation of SPNs more challenging.
DISCLOSURE: Lulette Tricia Bravo, No Financial Disclosure Information; No Product/Research Disclosure Information