Pathology of the Head and Neck

Maxillofacial Skeleton and Teeth Chapter 4 125With the onset of puberty, the lesions lose their activityand may mature to fibrous tissue and bone.There may also be a component consisting of immatureodontogenic tissue due to developing tooth germslying within the lesional tissue. This is a fortuitous findingwithout any clinical relevance.4.7 Neoplastic Lesionsof the Maxillofacial Bones,Non-OdontogenicTo be included in the following text, lesions should bemainly confined to the maxillofacial bones.Fig. 4.37. At high magnification, the vacuolated nature of thechordoma cells are clearly visible, as is their epithelial cohesion4.7.1 OsteomaICD-O:9180/0Osteomas are lesions composed of compact lamellarbone with sparse marrow cavities filled with fatty orfibrous tissue. In the maxillofacial skeleton, they mostcommonly occur in the frontal and ethmoid sinus; lessoften, the maxillary antrum and the sphenoid sinus areinvolved [137]. They may also occur in the jaw bones asa manifestation of Gardner’s syndrome [183].Paranasal osteomas as a group are common lesions[92]. Clinically, they cause sinusitis and headache or othersigns of sinonasal disease. Similar bony outgrowths atthe palate or mandible are called tori.4.7.2 ChordomaICD-O:9370/3Chordomas are malignant tumours derived from embryonicremnants of the notochord. The mostly occur ateither the cranial or caudal end of the vertebral column[57]. Chordomas show a slight male predominance; theymay occur at any age [57].Three different types of chordoma are discerned:conventional, chondroid, and dedifferentiated. Conventionalchordoma consists of lobules separated fromeach other by fibrous bands. These lobules containovoid cells with small, dark nuclei and homogeneouseosinophilic cytoplasm. Other cells show large vesicularnuclei and abundant cytoplasm with vacuoles.Sometimes, these cells contain only one single vacuolecausing a signet-ring appearance or vacuoles surroundingthe nucleus: these latter cells represent theso-called physaliphorous cells thought to be pathognomonicfor chordoma. In general, the cell density ismaximal at the periphery of the lobules; more centrally,the cells lose their epithelial cohesion and may lieisolated in an abundant mucoid matrix (Fig. 4.37). Althoughthere may be atypia, mitotic figures are infrequent.The lesion invades adjacent structures. Immunohistochemically,chordoma is characterised by positivityfor S-100 as well as vimentin and a broad varietyof epithelial markers [131].Chondroid chordoma (ICD-O:9371/3) denotes a variantof chordoma that contains cartilaginous areas indistinguishablefrom chondrosarcoma [57]. However,chondrocytic differentiation in chordomas probablyrepresents a focal maturation process [51]. Neitherhas the distinction between conventional and chondroidchordoma any clinical significance [29]. Therefore, it isadvocated that this designation be dropped. Dedifferentiatedchordomas are those lesions that contain areas ofchordoma as well as an additional malignant mesenchymalcomponent that may be a fibrosarcoma, an osteosarcomaor, most likely, a poorly differentiated sarcoma[64].Chordoma has to be distinguished from chondrosarcoma.Positivity for epithelial markers is a consistentfeature in chordomas and is absent in chondrosarcoma[132]. Other look-alikes, such as extraskeletal myxoidchondrosarcoma, myxoid liposarcoma and myxopapillaryependymoma, also lack positivity for epithelialmarkers [28]. Chordoid meningiomas may also mimicchordomas, but there are no physaliphorous cells, noris there positivity for cytokeratins in this meningiomasubtype [125].The differential diagnosis of chordoma should alsoinclude pleomorphic adenoma. Both lesions may showepithelial clusters as well as single cells with vacuolatedcytoplasm lying in a mucoid matrix. Moreover, positivityfor S-100, vimentin, and epithelial markers is displayedby both. Positivity for myoepithelial markers,however, is restricted to pleomorphic adenoma.Chordomas manifest by destroying adjacent structuresresulting in cranial nerve dysfunction. Rarely, theycause a swelling in the neck due to lateral growth. Theirsite precludes radical surgical treatment. Mostly, thera-