Diagnosis of granulomatous inflammation in thoracic small biopsies and fine needle aspiration specimens: a...

Small tissue biopsies aid in diagnosing infections; however, workup of inflammatory processes varies widely. We assessed the performance of small biopsies in identifying bacterial, mycobacterial, and fungal infections in granulomatous inflammation, using cultures as the gold standard, and described practice patterns across large U.S. academic institutions.

A multi-institutional retrospective electronic medical record review identified small thoracic biopsies (January 1, 2021-December 31, 2021) diagnosed as "granulomatous inflammation,", "non-necrotizing granulomatous inflammation", "necrosis only", and "acute inflammation." Clinical data, pathologic diagnoses, and special stain and culture results were collected.

All participating institutions perform rapid on-site examination and routinely order acid-fast bacilli stain (AFB) and Grocott's methenamine silver stain (GMS) for granulomatous inflammation. Of 584 patients, 358 were evaluated with special stains and cultures, 91 patients had an infectious organism on cultures, and 67 patients had positive stains. AFB and Fite sensitivities were 38.5% (95% CI: 20.2-59.4) and 11.1% (95% CI: 0.3-48.3), respectively with specificities of 97.4% (95% CI: 94.5-99.1) and 96.5% (95% CI: 87.9-99.6), respectively GMS sensitivity and specificity for fungal infection were 37.5% (95% CI: 15.2-64.6) and 92.1% (95% CI: 88.3-94.9). Special stains were more frequently positive with necrosis (P < 0.001) and cultures were more often positive in necrotic cases (P = 0.005).

Microbiologic cultures used with special stains result in the best diagnostic performance. Detection of granulomatous inflammation on morphologic assessment should prompt pathologists to order special stains (AFB and/or Fite and GMS) regardless of the presence of necrosis, especially in cases where cultures were not collected or resulted as negative but clinical suspicion remains high.