Hyalinizing spindle cell tumors with giant rosette-like structures.

We report two cases of hyalinizing spindle cell tumors with giant rosettes arising in the pararectal space and soft tissues of the wrist in a 46-year-old man and 22-year-old-woman, respectively. Microscopically, the tumors exhibited a varied morphology, including hyalinizing hypocellular and cellular fibromatosis-like areas. The most striking morphologic feature was the formation of giant rosette like structures with collagen cores scattered throughout the tumors. Most of the tumor spindle cells were diffusely immunoreactive for lysozyme, CD-68, factor XIII and vimentin. Reactivity for smooth muscle actin, desmin and S-100 protein was not found. Ultrastructural examination of the rosettes in one case only showed normal native collagen.