In October of 2006 a 41-year-old otherwise healthy man presented to the University of Maryland, Department of Oral and Maxillofacial Surgery for an evaluation of an expansile mass in the left zygomatic, preauricular region. Five months earlier the patient complained of headaches and increasing fatigue at the end of a normal work day. He then noticed increasing left jaw pain and trismus along with the headaches. He was seen and evaluated by his primary care physician. Initially he was treated for temporomandibular disorder. However, the patient's symptoms failed to subside and subsequently he was referred to an oral and maxillofacial surgeon. Computed tomography of his head and neck was obtained, revealing a destructive mass in the left condyle (Fig. ​(Fig.1).1). He was subsequently referred to the University of Maryland Medical Center for definitive treatment.

Hematoxylin-eosin stained sections showed a tumor mass remotely resembling a completely effaced lymph node, composed of a diffuse proliferation of large round to oval cells with pleomorphic vesicular nuclei, prominent nucleoli and abundant eosinophilic cytoplasm (Fig. ​(Fig.2).2). Sheets, fascicles, and whorls of spindle cells with spindled to ovoid vesicular nuclei, small to medium, distinct nucleoli, and eosinophilic cytoplasm were frequently observed (Fig. ​(Fig.3).3). Large multinucleated cells, mitotic figures (27/10 HPFs), and necrosis were also noted. There were numerous admixed lymphocytes, polymorphonuclear leukocytes, and less commonly, plasma cells. The neoplastic cells invaded the lymph node capsule, perinodal soft tissues and periosteum. They were strongly positive for CD163 (Fig. ​(Fig.4),4), CD68, lysozyme, NSE, and vimentin. Weak to moderate immunostaining for S-100, CD4, and CD45 were also noted. Reactive lymphocytes stained strongly for CD3, CD4, CD8, and to a lesser degree for CD20. Residual CD21 positive, and CD23 positive follicular dentritic cells were also seen (Fig. ​(Fig.5).5). The Ki-67 index was approximately 70% (Fig. ​(Fig.6).6). The neoplastic cells were negative for CD43, ALK, CD30, EMA, smooth muscle actin, cytokeratin, desmin, myogenin, TTF1, CD99, CD1a, LMP-1, CD117, HMB45, and Mart-1/Melan A. Electron microscopy revealed presence of numerous lysosomes and lack of desmosomes, Birbeck granules and interdigitating cell processes (Fig. ​(Fig.7).7). In situ hybridization for EBV-encoded RNAs was negative. Cytogenetic studies revealed a 57–80 hyperdiploid [7]/46, XY [13] karyotype, including 3 to 4 copies of various chromosomes.

Histiocytic and dendritic cell sarcomas are among the rarest of tumors affecting lymphoid tissues [1-5]. These tumors arise from phagocytes and related accessory cells, which have major roles in the processing and presentation of antigens to lymphocytes. Currently, the WHO includes the following 5 entities under this designation: histiocytic sarcoma (HS), follicular dendritic cell sarcoma (FDCS), interdigitating dendritic cell sarcoma (IDCS), Langerhans cell sarcoma (LCS), and dendritic cell sarcoma, not otherwise specified (DCS, NOS)[1]. The pathologic diagnosis of HS is often challenging and requires histologic, immunohistochemical, and, occasionally, electron microscopic analysis [1-5]. We reached the diagnosis of HS in our case based on the exclusion of other sarcomas and carcinomas including other members of the HS/dendritic cell sarcoma group. A comparison between immunophenotypes and ultrastructural features of the neoplastic cells of present case and reported lymphoid tissue phagocytic and accessory cell neoplasms is shown in Table ​Table11.

BAA and CJS processed the specimen, evaluated the immunohistochemical stains, confirmed the diagnosis, designed the report and drafted the manuscript.