PMC5985093_01
(a) Coronal MRI demonstrating a T1-hypointense lesion in the right proximal tibia with cortical destruction; (b) hematoxylin and eosin- (H&E-) stained section of the patient's tibia lesion demonstrating numerous eosinophilic histiocytes and emperipolesis (black circles).
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He underwent magnetic resonance imaging (MRI) which demonstrated progression of osteomyelitis with abscess formation, cortical breakthrough, and involvement of the surrounding soft tissue (Figure 1(a)). Findings again included mixed inflammatory cells, but now also involved abundant foamy histiocytes and eosinophilic histiocytes with emperipolesis, a phenomenon observed when other inflammatory cells (e.g., neutrophils, plasma cells, and lymphocytes) pass through the cytoplasm of a histiocyte (Figure 1(b)).