Morphology of bone marrow granulomas and etiologic considerations

histiocytes are referred to as granulomas and the respective infl ammatory process is called granulomatous. Granulomas are a well-known feature in pathology, with the fi rst description ranging back to the 17th century. Th ey show variable morphologic features including central areas of necrosis (necrotizing granulomas) or suppuration (microabsceding or suppurative granulomas), incorporation of foreign material or presence of giant cells due to the fusion of macrophages. Granuloma formation is usually associated with local CD4+ T-cell activation (and numeric increase of CD4+ T-cells at the site of granuloma formation, thus ‘consuming’ CD4+ T-cells and leading to skewing of the CD4/CD8 ratio in the peripheral blood in favour of CD8) and production of interleukin 2 and 12, Interferon (IFN) γ, and tumour necrosis factor α (TNF-α) [1, 2]. In general, granulomas are provoked by agents that are diffi cult to eradicate by the enzymes of histiocytes, for example because of the diff erent phospholipid composition of the former (e.g. mycolic acids) or because of the specifi c enzymo/immunogenetic background of the host. Th e number of causative agents in granulomatous responses is rather smaller than in other infl ammatory patterns. Th erefore granulomas are considered to be ‘specifi c’; narrowing down the possible causative factors, their identifi cation and subsequent search for possible underlying agents and conditions supports the establishment of more precise clinicopathological diagnoses.