Langerhans cell histiocytosis involving epiphysis of a long bone

Eosinophilic granulomas of long tubular bones, a form of Langerhans cell histiocytosis, occurs in metaphyses and diaphyses with equal frequency. Epiphyseal location is unusual, with only 13 cases previously reported in the literature. The present case involves the epiphysis of the upper end of the left femur in a 12-year-old boy with pain and limp in the affected area. Radiographic findings were an oval, radiolucent rarefaction with nonsclerotic border, measuring approximately 3.5 x 3.0 cm. Microscopic examination identified aggregates of histiocytes, multinucleated giant cells, scattered eosinophils, and few plasma cells and lymphocytes. Ultrastructural studies demonstrated Birbeck granules within cytoplasm of histiocytes diagnostic of Langerhans cell histiocytosis. Whether Langerhans cell histiocytosis is a neoplastic disorder or a reactive process remains controversial. The true nature of the Langerhans cell, the proliferating cells and hallmark of this disease, is likewise under scrutiny.