Parachordoma.

Parachordomas are rare soft-tissue neoplasms that are histologically similar to chordomas. They typically develop adjacent to tendon, synovium, or osseous structures within extremities and present as slowly growing, locally destructive, lobulated neoplasms that are prone to recurrence if incompletely excised. We report a parachordoma occurring in the right middle finger of a 25-year-old man. The neoplasm had been present for 5 years, and the patient had sustained repeated injuries to the area. Histologically, the lesion was characterized by well-circumscribed lobules composed of small cellular aggregates, some in "alveolar" distribution, and single, large, vacuolated (physalipherous) cells embedded within a hyalin and chondroid matrix divided by fibrous trabeculae. Immunohistochemically, the parachordoma stained positively for the S-100 protein, vimentin, and cytokeratin.