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Orbital mesenchymal chondrosarcoma is most common in the retrobulbar soft tissues and characteristically appears on CT as a heavily calcified welldefined mass, usually located in the muscle cone space. The calcifications may be so heavy as to be seen on plain film radiography. Not all lesions, however, demonstrate calcification. In the settings, it presents as a wellmarginated muscle cone mass with attenuation similar to that of the extraocular muscles.On dynamic contrast enhanced CT studies, mesenchymal chondrosarcoma demonstrates less rapid enhancement than nearby vascular structures [9].
The differential diagnosis of mesenchymal chondrosarcoma includes hemangiopericytoma, rhabdomyosarcoma, myxochodrosacoma, osteochondroma as primary orbital tumors and lymphoma, neuroblastoma, extraocular retinoblastoma, chloroma, synovial sarcoma and chondrosarcoma as tumors affecting the orbit secondarily (direct invasion or metastatic). Most of these tumors are round and oval shape histopathologically. Immunohistochemistry helps to differentiate among these tumors, such as desmin positivity in rhabdomyosarcoma, leucocyte common antigen positivity in lymphoma, neuronspecific enolase positivity in neuroblastoma, and vimentin and S100 positity in Mesenchymal tumors [1, 9, 12, 14]. Moreover, although the histologic appearance of the tumor is distinctive, its rarity, uncommon locations in the orbit, and high vascularity may lead to the erroneous diagnosis of a vascular tumor such as hemangiopericytoma [1]. In fact, our case was misdiagnosed as hemangiopericytoma at the first pathological diagnosis after operation and the diagnosis of mesenchymal chondrosarcoma was made by histological examination and immunohistochemistry vimentin and S100 positivity after the second operation.
Most mesenchymal chondrosarcomas are resistant to chemotherapy and radiotherapy. The surgical resection is the mainstay of therapy. Complete removal of the tumors either by orbital resection or by exenteration may be adequate in some cases. However, if the tumor cannot be resected or seems histologically aggressive, chemotherapy and radiation therapy should be considered [1]. If thorough resection is difficult by preoperative estimation, radiotherapy and/or chemotherapy may be given so as to thorough resection. Tuncer et al[1] reported a case of 5monthold girl who received one course of vincristine, actinomycinD, and cyclophosamide and then two courses of ifosfamide, epirubicin and cisplatin (IEC), and then radiation therapy. After three courses of chemotherapy and radiotherapy, exenteration was carried out because the margin between the tumor and the globe remained indistinct. Postoperatively, three courses of IEC chemotherapy were administered. The patient was cured at last. In a review, 10 cases of extraskeletal mesenchymal chondrosarcoma have been reported by Jacobs et al [12]. In this study, the orbit was exenterated in four cases; and in other six cases, the tumor was resected. Only adjuvant radiation therapy was used in two cases, whereas both radiation and chemotherapy were used in the other two cases. Of these four patients, two patients died after 5 years and 6 months after treatment respectively.
The prognosis for patients with orbital mesenchymal chondrosarcoma is acceptable. In the Chinese literature [38], the shortest followup is 1 year and the longest is 11 years with no evidence of disease [8]. In the 18 cases reviewed and reported by Tuncer et al[1], seven patients was not clearly followed up. In the other 11 patients, three patients died after 6 months, 2 years and 5 years after treatment because of widespread metastasis, local recurrence, and treatmentrelated toxicity respectively, and eight patients were known to have survived for 5 to 18.5 years after treatment. Our patient has survived 2 years after the first operation and now is followed up.
In conclusion, orbital mesenchymal chondrosarcoma is extremely rare, with only eight published cases in the Internetbased Chinese literature, including one case of orbital mesenchymal chondrosarcoma misdiagnosed as hemangiopericytoma at first. Immunohistochemistry vimentin and S100 positivity help to differentiate it. The prognosis is related to the quality of surgical resection and the additional chemotherapy and/or radiotherapy in case of incomplete resection.
Acknowledgement We gratefully acknowledge the help of Department of Pathology of West China Hospital, Sichuan University.
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