LAUSR

A 19-year-old male presented for a painless mass with associated swelling over the right side of his jaw. Imaging performed a few days prior showed an enhancing osseous and extraosseous mass involving the right greater wing of the sphenoid bone and the anterior right temporal bone with adjacent masseter and temporalis muscle invasion. Direct smears obtained from a computed tomography (CT)guided fine-needle aspiration showed a cellular specimen composed of numerous histiocytes with occasional multinucleated giant cells in an inflammatory background (Figure 1). On higher power examination, the histiocytes exhibit folded, grooved nuclei with small nucleoli, and abundant cytoplasm (Figure 2). The cell block preparation was significant for numerous large, pale mononuclear cells with abundant pink cytoplasm admixed with numerous eosinophils, and necrosis distributed throughout the sample (Figure 3). To further characterize this cellular population, immunohistochemical stains were performed to demonstrate that the cells of interest were strongly reactive for CD1a (Figure 4) and S-100 (Figure 5), but were negative for CD30, melan-A, pancytokeratin, and CD138. The aspirate was diagnosed as eosinophilic granuloma. Eosinophilic granuloma is the mildest and most localized form of Langerhans cell histiocytosis (LCH). It typically involves the soft tissue and bone of children and young adults (<20 years) with a male to female ratio of 2:1. It includes a spectrum of heterogeneous disorders, all of which contain a clonal proliferation of abnormal CD1a+/CD207 (Langerin) positive histiocytic Langerhans cells (LCs). The disease may be broadly categorized as multisystem (involving two or more organs), multifocal (involving multiple sites in one organ system), or single system (involving one site only, as in our case). LCH is defined as an inflammatory myeloid neoplasm as LCs demonstrate phenotypic expression of myeloid dendritic cell markers and contain Birbeck granules, which are the associated electron microscopic feature. However, the diagnosis now only necessitates immunoreactivity to either CD1a or CD207.