Radiological aspects of osteosarcoma of the jaws1. IntroductionOsteosarcoma of the jaw has a pattern of presentation and behaviour which distinguishes it from osteosarcoma at other sites. It occurs in a more elderly population, is less aggressive and has a tendency to spread locally rather than produce distant metastases. It is more frequent in women and in people in their thirties and forties, the mandible being more often affected than the maxilla. Paget's disease, fibrous dysplasia and previous irradiation of the facial region are conditions associated with its development.Radiographic evaluation is important in diagnosis, because clinical symptoms, such as pain, paresthesia, swelling and loose teeth, are not specific. Diagnosis by conventional radiography is difficult and should be supplemented by CT, which aids in distinguishing the lesion from surrounding or superimposed structures. The radiological features are not however pathogno-monic, as jaw bone neoplasias are highly variable in both macroscopic and radiological appearance. For this reason a radiological classification of osteosarcoma of the jaw does not exist. Previous authors have not investigated the radiological features exhaustively, nor has a series of more than five cases been adequately documented by both conventional radiology and CT.In this paper we present conventional and CT radiological ndings of nine patients with osteosarco-ma of the jaws.

Figure 1 Case I. Axial CT scan shows a type I non-ossifiedosteosarcoma that occupies the right maxillary sinus and hasdestroyed the bone margins, expanding into both the nose and theinfratemporal spaces

Figure 2 Case 6. Coronal CT scan showing the palatal extension ofa small type II osteosarcoma with mottled ossification within theneoplastic mass (arrowheads)

Figure 3 Case 8. (a) Axial CT scan shows patchy ossification of the neoplastic tissue in a type II osteosarcoma of the maxillary alveolar process (arrows). (b) After tumour resection, a recurrence rapidly developed with invasion into the maxillary sinus, destruction of bone walls and infiltration into adjacent soft tissue. The lesion shows diffuse neo-osteogenesis with clearly visible bony spicules, particularly around the pterygoid process (arrowheads)

Figure 4 Case 2. Axial CT clearly shows lamellar neo-osteogenesisat both buccal and lingual cortices, as well as soft tissue invasion, ina type III osteosarcoma of the mandible

Figure 5 Case 5. Axial CT of a case of type III mandibular osteosarcoma. (a) Disruption of normal mandibular architecture is evident with bone windowing, but the very fine buccal new-bone lamellae are only just visible. (b) Infiltration of the buccal soft tissues is clearly demonstrated with soft tissue windowing which also enables better visualization of the fine lamellae

Figure 6 Case 4. (a) Axial CT demonstrates irregular osteolysis of cancerous bone and lingual cortex, as well as lamellar neo-osteogenesis, mostly on the buccal side, in a typical type III osteosarcoma of the mandible. (b) Radiograph of the resected specimen clearly depicts fine lamellae arising perpendicularly on the buccal cortex. (c) Relapse of the osteosarcoma is characterized by extensive and gross new bone formation at the margins of the resection.

DiscussionEvaluation of the cases reported here suggests that the radiological presentation of osteosarcoma of the jaw may be classified into three categories, which can only be identified with certainty using CT, a method that gives a precise picture of the anatomy of the tumour and especially of its degree of ossification. In the first type, with no ossification, conventional radiology reveals non-specific destruction of bone, indistinguishable from bone erosion caused by a carcinoma or from fibrous dysplasia in its very early stages.In the second type, with mottled ossification, the small amount of calcified tissue can be better orexclusively visualized by CT. Fibrous dysplasia and ossifying fibroma in the initial phase of bone formation also have the same radiological presentation. How-ever, being benign, these lesions have well-defined borders and do not invade the cortex even when large.The third type, with lamellar ossification, was the most common in our series. In most cases it was visible with conventional radiography;CT separates fine lamellae from adjacent structures and makes diagnosis easier in the less typical cases. Although lamellar ossification can be a feature of other conditions, it provides a basis for inclusion of osteosarcoma in the difierential diagnosis.21It is important to emphasise that osteosarcomas of the second type were in our experience much smaller in size than those of the third type. It is hard to say whether amorphous ossification is characteristic of the early stages of the tumour, or whether lamellar ossification is a consequence of the particular embryological development of the mandible. We have no evidence to support the hypothesis that amorphous ossification is characteristic of early stages of the development of the tumour, whereas lamellar ossification appears at a later stage, although our observation that a small tumour of the maxilla with amorphous ossification (case 8) recurred after surgery, producing a larger mass containing typical lamellae, may be indicative.

It is also dicult to sustain the theory that the embryology of the mandible could explain lamellarneo-osteogenesis, because lamellar ossification is typical of osteosarcoma occurring at other sites, particularly in the long bones. Identification of recurrence after surgery was easy in the three cases we studied, as the osteosarcoma became aggressive and invaded surrounding structures early andextensively. The radiological features were typical, with large visible bony lamellae throughout theneoplastic tissue and extensive infiltration of soft tissues. Overall, on the basis of this series, we found CT to be much superior to conventional radiography in identifying bone erosion, soft tissue inltration and neoplastic tissue ossification, especially of the amorphous type. Since histological diagnosis maybe dicult18 because of the small biopsy samples available, and since conventional radiology under-estimates the extent of neoplasm,13 CT is crucial both for an early diagnosis of osteosarcoma of thejaw and for accurate planning of the extent of surgery.