Fibroma of Tendon Sheath : Microscopic
A typical case of fibroma of tendon sheath is relatively hypocellular. There are lobules with sparse numbers of bland spindle cells in a dense collagenous stroma adjacent to zones of myxoid change containing stellate cells. The spindle cells have uniform elongated nuclei with punctate nucleoli. Rare cases show significant nuclear hyperchromasia and pleomorphism (degenerative-type atypia) and such cases have been referred to as pleomorphic fibroma of tendon sheath. They lack the cellularity, increased mitotic activity and atypical mitoses and should not be mistaken for pleomorphic sarcoma. In areas of increased cellularity, the spindle cells may be arranged in storiform or fascicular pattern resembling nodular fasciitis. Mitotic figures are infrequent and normal in morphology.