Granulomas in bone marrow

Although aggregates of histiocytes may be present on aspirate smears, granulomas are best identified with bone marrow trephine and clot biopsy materials (Bodem et al., 1983; Bhargava & Farhi, 1988; Vilalta-Castel et al., 1988; Foucar, 2001; Chang et al., 2003). Granulomas in the bone marrow should be approached in a similar fashion to those in other sites.

There are generally two types of granulomas encountered in the marrow. The lipogranuloma is a collection of histiocytes surrounding adipose tissue and is usually not associated with disease (Rywlin & Ortega, 1972) (Fig. 3.1). Epithelioid granulomas without associated adipose tissue may have admixed lymphocytes, plasma cells, neutrophils, or eosinophils and may have associated necrosis (Fig. 3.2). Mycobacteria and fungal organisms should be excluded by special stains in all cases with epithelioid granulomas, and fresh bone marrow aspirate material should be submitted for culture in all patients being evaluated for infectious diseases.

The most common causes of infectious granulomas are summarized in Table 3.1. Patients with immunodeficiency syndromes may have a disseminated atypical mycobacterial infection caused by Mycobacterium avium–intracellulare (MAI) even when well-formed granulomas are not present. In such cases, special stains for organisms are indicated when any increase in histiocytes is noted. MAI may also be associated with the presence of “pseudo-Gaucher” macrophages in which the intracellular organisms mimic the characteristic cytoplasmic striations of Gaucher cells. MAI shows a characteristic periodic acid-Schiff (PAS) positivity, while in tuberculosis the organisms are usually PAS-negative (Fig. 3.3).