Amianthoid fibers in a synovial sarcoma and a malignant schwannoma.

Amianthoid collagen fibers having typical collagen periodicity, but measuring up to 1000 nm in thickness, were observed in a synovial sarcoma of the leg and a malignant schwannoma of the orbit. Intracellular amianthoid fibers were present in the cytoplasm of many of the synovial sarcoma cells. The tumor cells in both lesions appeared to be actively synthesizing these unusual fibers.