Sections of the bone show an area of loose fibrous tissue with oedema in the medulla. There are several aggregates of epithelioid cells with large indented vesicular nuclei, intranuclear grooves and prominent nucleoli in a background of lymphocytes, plasma cells, pigment-laden macrophages and occasional multinucleated giant cells. Eosinophilia is not a feature. No granulomas are present. Atypical mitoses are not seen. The overall features are suggestive of Langerhans' cell histiocytosis. However, these clusters of epithelioid cells have cut-out on the immunostained slides and therefore, the diagnosis cannot be confirmed.
FINAL DIAGNOSIS: Morphological features suggestive of Langerhans' cell histiocytosis.