Answer: Osteomyelitis

Histology: The histologic features show a heterogeneous mixture of inflammatory cells. These include neutrophils, histocytes, lymphocytes and plasma cells. In addition, there is some marrow fibrosis. The inflammatory tissue, in the present radiographic setting, is consistent with acute osteomyelitis. The absolute diagnosis of osteomyelitis, however, rests on positive wound and intraoperative cultures.

Discussion: Although the lesion is radiographically consistent with the Ewing’s sarcoma, the histologic pattern of inflammatory tissue rules this diagnosis out. Complicating this difficult differential diagnostic problem of Ewing’s tumor vs osteomyelitis is the fact that many patients with Ewing’s sarcoma present with an elevated white count, a high fever, and an elevated sed rate. This makes the clinical and radiographic presentation of Ewing’s tumor and acute osteomyelitis identical. The differential diagnosis rests on a biopsy.

Although eosinophilic granuloma presents with a heterogeneous mixture of inflammatory cells, the histocytes in eosinophilic granuloma are positive with S-100 protein and CD 1A. Because of similarities of radiographs ad H & E patterns, these immunohistochemical stains should be performed in all cases of presumed osteomyelitis in order to rule out Langerhans’ cell histiocytosis.