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A 63-year-old man reported a 2-year history of painless OS proptosis. The first MRI, performed in the institution of origin, resulted in a diagnosis of hemangioma versus orbital pseudotumor. Examination revealed proptosis and mild chemosis. Ancillary tests were normal, and oral prednisone was initiated without remarkable changes. Later, an incisional biopsy identified the lesion as an intramuscular myxoma of the left rectus, and a new MRI was ordered. It described a fusiform thickening of the medial rectus with and exophytic growth below the inferior rectus and upward toward the superior oblique. Due to the localization of the lesion, a combined transcaruncular and swinging eyelid approach with a lateral orbitotomy was performed. Histopathological examination revealed a proliferation of stromal origin composed of myxoid matrix with fusocellular and stellate-shaped cells. Cells were S-100, CD34, and CD56 positive and negative for epithelial membrane antigen, CD68, CD10, actin, and desmin. Results were consistent with a left medial rectus nerve sheath myxoma.

Metaplasia is the production by cells of a kind of tissue other than that corresponding to their lineage, ie it represents the conversion of one tissue into another. Bony metaplasia has frequently been described in polyps of the gastrointestinal tract. In nasal polyposis it is an extremely uncommon finding. We describe the case of a 42 year-old female presenting nasal obstruction due to a unilateral nasal tumour. She was operated on by means of endoscopic sinonasal surgery and the definitive diagnosis was nasal polyposis with areas of bony metaplasia.

La metaplasia es la produccion por parte de las celulas de un tipo de tejido distinto del de su estirpe; es el cambio de un tejido en otro. La metaplasia osea ha sido descrita en polipos del tracto gastrointestinal con cierta frecuencia. En la poliposis nasal es un hecho extremadamente infrecuente. Describimos el caso de una paciente de 42 anos con clinica de obstruccion nasal; presentaba una tumoracion nasal unilateral y fue intervenida mediante abordaje endoscopico nasosinusal. El diagnostico definitivo fue poliposis nasal con areas de metaplasia osea.