The arrow points to a bony spicule containing lacunae with viable osteocytes. The intervening fibrous stroma has spindly to oval fibroblast nuclei scattered within eosinophilic collagen. The monostotic form is the most common, and is usually diagnosed at early adulthood. The polyostotic form may be diagnosed earlier, due to the more wide-spread bone disease. Grossly, the lesion can be clearly seen from the rest of the bone as a circumscribed tan-white area.
Larger lesions tend to expand and distort the bone in which they occur.
They have a gritty consistency due to the presence of trabeculae of bone. Histologically, the tissue is composed of loose fibrous connective tissue in which isolated, typically curved pieces of bony trabeculae can be seen. The most common is monostotic with a single focus involving usually the skull or the long bones. The monostotic variety is clinically relatively silent and may be detected in routine X-rays. Rarely, it may cause a pathological fracture of bone.