Pathology of the Head and Neck

Maxillofacial Skeleton and Teeth Chapter 4 121Table 4.3. Fibro-osseous lesions [13, 181]Fibrous dysplasiaOssifying fibromaOsseous dysplasiaConventionalJuvenile trabecularJuvenile psammomatoidPeriapical osseous dysplasiaFocal osseous dysplasiaFlorid osseous dysplasiaFamilial gigantiform cementomade novo or from a pre-existing ameloblastic fibroma orameloblastic fibro-odontoma [98].Those extremely rare lesions that combine carcinomatousand sarcomatous elements, but are recognisableas odontogenic from the epithelial component, resembleameloblastic carcinomas, and have been called odontogeniccarcinosarcoma or odontogenic carcinoma with sarcomatousproliferation [152].4.5 Fibro-Osseous LesionsThe current classification of maxillofacial fibro-osseouslesions includes fibrous dysplasia, ossifying fibroma andosseous dysplasia [13, 158]. Table 4.3 gives an overviewof the various entities in this group.4.5.1 Fibrous DysplasiaFibrous dysplasia is composed of cellular fibrous tissuecontaining trabeculae of woven bone. It occurs in threeclinical subtypes: monostotic, which affects one bone,polyostotic, which affects multiple bones, and Albright’ssyndrome, in which multiple bone lesions are accompaniedby skin hyperpigmentation and endocrine disturbances[13]. Activating missense mutations of the geneencoding the α subunit of the stimulatory G protein area consistent finding in the various forms of fibrous dysplasia[123].Craniofacial fibrous dysplasia is usually of the monostotictype [44]. The disease mostly occurs during thefirst three decades, although cases are occasionally seenat an older age. The maxilla is more often involved thanthe mandible. In the maxilla, fibrous dysplasia may extendby continuity across suture lines to involve adjacentbones [13].Fibrous dysplasia shows replacement of the normalbone by moderately cellular fibrous tissue containingirregularly shaped trabeculae consisting of wovenbone without rimming osteoblasts that fuse with adjacentbone. Jaw lesions may also show lamellar bone(Fig. 4.28). Sometimes, tiny calcified spherules may bepresent [158].Fig. 4.28. In the jaws, fibrous dysplasia may consist of both wovenand lamellar bone, as shown in this photomicrograph takenwith the use of partly polarised light to enhance the collagenousscaffold of the boneFibrous dysplasia has to be distinguished from otherlesions characterised by the combination of fibrous tissueand bone: ossifying fibroma, osseous dysplasia, lowgradeosteosarcoma and sclerosing osteomyelitis. However,none of these is composed of woven bone trabeculaefusing with adjacent uninvolved bone. Ossifying fibromaand osseous dysplasia both show much variety inappearance of mineralised material and stromal cellularity,low-grade osteosarcoma invades through the corticalbone into soft tissues and sclerosing osteomyelitisshows coarse trabeculae of lamellar bone, whereas theintervening stroma is not cellular but oedematous withsprinkled lymphocytes [158].Fibrous dysplasia clinically presents as a painlessswelling of the bone involved. Radiographically, the classicalappearance is described as orange-skin or groundglassradiopacity without defined borders [13]. Usually,fibrous dysplasia is a self-limiting disease. Therefore,treatment is only required if there are problems due tolocal increase in size of the affected bone. Sometimes, anosteosarcoma may arise in fibrous dysplasia [39].4.5.2 Ossifying FibromaICD-O:9262/0, 9274/0Ossifying fibroma , formerly also called cemento-ossifyingfibroma is a well-demarcated lesion composed offibrocellular tissue and mineralised material of varyingappearance. It occurs most often in the 2nd through the4th decades. The lesion shows a predilection for females,is mostly seen in the posterior mandible [13] and mayoccur multifocally [70].Chromosomal abnormalities have been observed inossifying fibromas [31, 49, 138]. Data are still too scarceto determine their pathogenetic significance.