Pathology of the Head and Neck

122 P.J. Slootweg4Fig. 4.29. Ossifying fibroma contains both cell-rich and cell-poorareas as well as well-structured bone and amorphous calcified materialFig. 4.31. Juvenile trabecular ossifying fibroma shows slenderbony trabeculae rimmed with osteoblasts that merge with an extremelycellular stromaFig. 4.30. Ossifying fibroma may also contain more smoothlycontoured bony elements, formerly thought to represent cementumFig. 4.32. At higher magnification, the plump osteoblasts thatline the bony trabeculae in juvenile trabecular ossifying fibromaare shown to be a prominent featureOssifying fibroma is composed of fibrous tissue thatmay vary in cellularity from areas with closely packedcells displaying mitotic figures to almost acellular sclerosingparts within one and the same lesion. The mineralisedcomponent may consist of plexiform bone, lamellar boneand acellular mineralised material, sometimes all occurringtogether in one single lesion (Figs 4.29, 4.30).Juvenile psammomatoid and juvenile trabecular ossifyingfibroma are subtypes [40]. Juvenile trabecularossifying fibroma consists of cell-rich fibrous tissuewith bands of cellular osteoid together with slendertrabeculae of plexiform bone lined by a dense rimof enlarged osteoblasts (Figs. 4.31, 4.32). Sometimesthese trabeculae may anastomose to form a lattice.Mitoses are present, especially in the cell-rich areas.Also, multinucleated giant cells, pseudocystic stromaldegeneration and haemorrhages may be present. Dueto its cellularity and mitotic activity, the lesion may beconfused with osteosarcoma. However, atypical cellularfeatures or abnormal mitotic figures are not seen.Moreover, the lesion is demarcated from its surroundings[73, 158, 181].Juvenile psammomatoid ossifying fibroma is characterisedby a fibroblastic stroma containing small ossiclesresembling psammoma bodies, hence its name. Thestroma varies from loose and fibroblastic to intenselycellular. The spherical or curved ossicles are acellularor include sparsely distributed cells (Fig. 4.33). Theyshould not be confused with the cementum-like depositsthat are present in conventional ossifying fibroma.These particles have a smooth contour whereas the ossiclesin juvenile psammomatoid ossifying fibroma hasa peripheral radiating fringe of collagen fibres. Ossiclesmay coalesce to form trabeculae. Sometimes, juvenilepsammomatoid ossifying fibroma contains basophilic,concentrically lamellated particles, as well as irregularthread-like or thorn-like calcified strands in a hyalinisedbackground (Fig. 4.34). Other features such as trabeculaeof woven bone as well as lamellar bone, pseudocysticstromal degeneration and haemorrhages resulting