Chondromyxoid fibroma is a benign tumor characterized by lobules of spindle-shaped or stellate cells with abundant myxoid or chondroid intercellular substance. The long bones are the sites most frequently affected, involvement of the skull and facial bones being less than 5 % [1]. Radiologically, they show an irregular radiolucency due to destruction of cancellous bone (Figs. 10.1 and 10.2).

The histologic features include the presence of stellate or spindle-shaped cells in a myxoid background, arranged in lobules (Fig. 10.3). The interlobular tissue is cellular and also composed of oval or spindle-shaped cells. Multinucleated giant cells may be present at the border of the lobules in approximately 50 % of tumors (Figs. 10.4 and 10.5). Calcification and/or hyaline cartilage is seen in a minority of cases (Fig. 10.6). Focally, nuclear atypia, binucleate cells and mitotic figures may be observed (Fig. 10.7) and metaplastic ossification may change the appearance of the chondroid matrix (Fig. 10.8). In some cases, the lobularity is not very conspicuous, the tumor only showing a diffuse proliferation of stellate-shaped cells in a loose myxoid background (Fig. 10.9). The lesion shows demarcation from adjacent soft tissues by an expanding and attenuated cortical rim but there is no demarcation between the tumor and adjacent cancellous bone in which the tumor may invade (Figs. 10.10 and 10.11).

The clinically most relevant histologic differential diagnosis is with chondrosarcoma that may also have a lobulated growth pattern, myxoid matrix, and spindling of the nuclei. However, chondromyxoid fibromas typically contain cells with small, oval- to spindle-shaped nuclei without atypia whereas the nuclei in chondrosarcomas are usually larger, hyperchromatic, and with some degree of atypia. In those cases of chondromyxoid fibroma that show some atypical features as mentioned above and illustrated in Figure 10.7, the lobularity of the lesion will be helpful in differentiating between both diagnostic possibilities. In chondromyxoid fibromas of the skull base, chordoma may be considered as an alternative diagnosis. Chordomas contain epitheloid cells arranged in nests and cords and with vacuolated cytoplasm. Moreover, the chordoma cells are positive with cytokeratin markers. For further details on chordoma, see Chap. 11.

Regarding treatment, jaw resection has been recommended for extensive lesions whereas smaller lesions may be treated by curettage only [2].

Chondroblastoma is a benign, cartilage producing neoplasm. Less than 10 % of them occur in the maxillofacial skeleton, especially in the lateral part of the temporal bone [1, 3]. Due to this site, hearing loss may occur.

Chondroblastomas are composed of mononuclear cells and chondroid matrix (Fig. 10.12). The mononuclear cells have an oval-to elongated nucleus that may display a characteristic longitudinal groove. Sometimes these cells contain brown granular pigment (Fig. 10.13). Mitotic figures are usually present, but not numerous. Multinucleated giant cells are a common feature (Fig. 10.14). Chondroid matrix varies in amount. Approximately one third of chondroblastomas exhibit calcification, usually occurs in a chickenwire-like pattern (Fig. 10.15). Secondary aneurysmal bone cyst formation may occur in one third of cases (Fig. 10.16) [1].