Image Quiz: Cytology-A chalky white-filled lesion in a German shepherd

A 2-year-old German shepherd is presented for evaluation of a subcutaneous nodule over the olecranon region of the elbow. The nodule is extremely firm, and material obtained through fine-needle aspiration is gritty and chalky white. Unstained, with the microscope condenser lowered, the material appears refractile. After staining with Wright's-Giemsa stain, little is apparent except for a stippled background, small numbers of red blood cells, and occasional macrophages-a few that are multinucleated.

What is the most likely diagnosis for this lesion?

a) Lipoma

b) Hygroma

c) Osteosarcoma

d) Calcinosis circumscripta