Nuchal fibrocartilaginous pseudotumor: immunohistochemical and ultrastructural study of two cases.

Two cases of nuchal fibrocartilaginous pseudotumor are reported. The lesions occurred in a 50-year-old woman and a 41-year-old man. From the clinical point of view, the absence of history of trauma in one case represents an unusual observation. Histologically, both lesions were similar to the 10 cases which have been previously described. They consisted of poorly defined, moderately cellular fibrocartilage nodules, and they lacked nuclear atypia and mitotic activity. Immunohistochemically, the lesions showed diffuse expression of vimentin and CD34. Mild expression of S-100 was limited to some chondroid cells. Desmin, alpha-smooth muscle actin, and CD99 (MIC2 gene product) were not expressed. Ultrastructurally, cells with features of fibroblasts and chondroblasts without any signs of myofibroblastic or myochondroblastic differentiation were found.