Ultrastructural study of benign osteoblastoma of the maxilla.

The ultrastructure of benign osteoblastoma of the maxilla in a 14-year-old boy was studied. Morphologically, the tumor tissue was composed of abundant osteoid of a trabecular form, and cellular and vascular connective tissue. The cellular components were osteoblasts, osteoclasts, osteocytes entrapped within the osteoid, and small perivascular cells of two types. The small cells of one type were ovoid and had a relatively large nucleus and a dark cytoplasm. The cells of the other type were elliptical and had a clear cytoplasm. The former seemed to be a preosteoblast and the latter could not be identified. The osteoblast was the predominant cell in this lesion and was characterized by the presence of abundant rough-surfaced endoplasmic reticulum and several Golgi complexes. These characteristics indicated the pronounced activity of collagenous fiber synthesis and the matrix of the osteoid tissue.