Necrotizing granulomatous inflammation: what does it mean if your special stains are negative?

Necrotizing granulomas are commonly encountered in surgically resected specimens. The majority will be proven infectious with special stains for microorganisms. These need to be distinguished from other granulomatous processes such as Wegener's granulomatosis (WG). Although there may be histological overlap between these different processes, the identification of a true necrotizing vasculitis is specific to WG in the context of necrotizing granulomas. Otherwise, the combination of histological features should lead to a specific diagnosis. Despite a thorough histological examination and assessments of special stains, a significant proportion of necrotizing granulomas will appear infectious with no obvious infectious etiology. There are only few clinically available ancillary tests that can be performed on paraffin-embedded tissue and include real-time PCR for tuberculous mycobacteria. Despite correlation with clinical, serological and other microbiological studies, some necrotizing granulomas remain unexplained. Patients with such granulomas appear not to require any additional treatment and do experience a favorable outcome.