Clinical history of patients with surface osteosarcoma depen
Clinical history of patients with surface osteosarcoma depends on its grade of malignancy. In low grade lesions and especially in cPOS, symptoms are most often of prolonged duration . However, in HGSO and DPOS—especially when the dedifferentiation is synchronous—clinical history is not distinguishable from that of conventional osteosarcoma. In our study, the mean duration of symptoms was longer in low and intermediate grade lesions than in high grade lesions (16±4.66 months vs. 12±4.14 months). However the difference was not statistically significant.
Distinctive features between cPOS and DPOS are debatable. As observed in our series (25% vs. 100%), invasion of the medullary canal is more frequent in cPOS then in DPOS [3,4]. However, this cannot distinguish DPOS from cPOS according to Sheth et al. . Other distinctive features were reported. Bertoni  studied the meaning of radioloucencies in parosteal osteosarcomas and concluded that the presence of deep intralesional radiolucencies within a parosteal osteosarcoma strongly suggests the possibility that the lesion is dedifferentiated.
Medullary involvement is also discussed in periosteal osteosarcomas and HGSO. Some authors think that this sign precludes the diagnosis of surface osteosarcoma  while others have described periosteal osteosarcoma with microscopic or gross medullary involvement [8,9].
Currently, surgery is the main therapeutic procedure for surface osteosarcoma. Wide resection is recommended to achieve safe margins. Some authors advocated local excision for cPOS with marginal margins [10–12]. Indeed, resection of the cortical on which the cPOS is developed when the medullary canal is not invaded can be safe. Two cases had cortical resection with wide margins did not recur in our series. However, intralesional resection is absolutely prohibited because it Merimepodib is associated with high rate of local recurrence and high risk of dedifferentiation. In our experience, all cases in which resection was intralesional recurred. In one case, the tumor underwent dedifferentiation 4 years after first excision.
For high grade lesions (DPOS and HGSO), margins have to be as wide as possible in. One of the problems of these lesions is the assessment of the true extension of the tumor in the subperiosteal plane. According to Revell , even with axial MRI and CT, this can be difficult. These tumors are very permeative and spread further than can be assessed by MRI, and hence wider margins than might at first be considered are mandatory for safety. In the current study, three lesions recurred despite wide resections.
Chemotherapy has limited benefit in surface osteosarcoma. Rose  showed no benefit of chemotherapy in PerOS. Degree of necrosis that he observed in patients that received doxorobucine, ifosfamide and methotrexate was similar to the spontaneous necrosis seen in resected specimens from the other patients. Bertoni  reported poor response in all patients with DPOS that received neoadjuvant chemotherapy. Even for survival rate, the role of chemotherapy was not clear. Revel  reviews a series of 17 PerOS. Among 10 patients who received neoadjuvant chemotherapy, only 2 had greater than 90% necrosis. Although, both authors [4,5] recommended by caution the use of neoadjuvant chemotherapy for DPOS and PerOS respectively.
Conclusion Surface osteosarcomas are rare but they cover a wide spectrum of lesions. We think that there are 2 kinds of lesions:
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Background Chordomas, rare malignant tumors that originate in embryonic notochordal remnants, account for 1–4% of primary malignant bone tumors . Their origin from notochordal cells was first reported by Muller in 1858; the tumors were named by Ribbert in 1894. Their incidence is only 0.5–0.8/million and they account for 17.5% of primary malignant bone tumors in axial bones [1,2]. Most chordomas occur in the sacrococcygeal region. About 50–60% originate in the sacrum, and 15% in the skull and mobile spine [3,4]. Chordomas in other sites are extremely rare.