title: Primary orbital mesenchymal chondrosarcoma: a case report and literature review.
abstract: BACKGROUND
  Mesenchymal chondrosarcoma (MC) is a subtype of chondrosarcoma, with an incidence varying from 1 to 8% of all chondrosarcomas. It is an aggressive neoplasm with a high tendency for late recurrence and occasional delayed distant metastasis. Orbital MC is very rare, and only approximately 30 cases have been described in the literature. We describe here one case of primary orbital MC.
  
  
  METHODS
  A 14-year-old boy without a past medical history presented with a 1-month history of progressive proptosis on the right eye. Computed tomography (CT) scans of the orbit revealed a right intraconic lesion, with areas of calcification. The lesion was excised. Histopathological analysis revealed that the tumor had a biphasic pattern, showing a combination of small cell malignancy and well-differentiated cartilage. Immunohistochemistry examination revealed a diffuse membrane expression of CD99 on the small cell malignancy; S-100 was positive only within the cartilage component. The patient received chemotherapy, and no metastatic disease was found at the 2-month follow-up.
  
  
  CONCLUSIONS
  Although rare, MC should be considered in the differential diagnosis of a well-circumscribed orbital lesion in young adults, especially when CT scans reveal areas of calcification within the tumor.
authors.affiliation: Department of Ophthalmology, Sociedade Beneficente Santa Casa, Campo Grande, MS, Brazil. alexandrenakao@yahoo.com.br
authors.forename: Alexandre Nakao
authors.initials: AN
authors.lastname: Odashiro
authors.forename: Lívio Viana O
authors.initials: LV
authors.lastname: Leite
authors.forename: Rodrigo Sanches
authors.initials: RS
authors.lastname: Oliveira
authors.forename: Camila
authors.initials: C
authors.lastname: Tamashiro
authors.forename: Patrícia Rusa
authors.initials: PR
authors.lastname: Pereira
authors.forename: Luciana N Odashiro
authors.initials: LN
authors.lastname: Miiji
authors.forename: Danilo Nakao
authors.initials: DN
authors.lastname: Odashiro
authors.forename: Miguel N
authors.initials: MN
authors.lastname: Burnier
mesh_terms: D000071443:12E7 Antigen; D000293:Adolescent; D015703:Antigens, CD / Q000032:analysis / Q000096:biosynthesis; D002114:Calcinosis / Q000175:diagnosis; D002356:Cartilage / Q000378:metabolism / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000032:analysis / Q000096:biosynthesis; D018211:Chondrosarcoma, Mesenchymal / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D003937:Diagnosis, Differential; D004358:Drug Therapy; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism / Q000473:pathology; D009918:Orbital Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D009418:S100 Proteins / Q000032:analysis / Q000096:biosynthesis; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D000071443:12E7 Antigen; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D009418:S100 Proteins