Details
41-year-old woman with right paraspinal mass.
Desmoid-type fibromatosis is an intermediate (local aggressive), non-metastasizing, myofibroblastic neoplasm that is characterized by infiltrative growth and local recurrence. Most cases are sporadic and occur generally in younger individuals in either intra-abdominal (mesentery, retroperitoneum, pelvis) or extra-abdominal (shoulder, chest wall, back, thigh, head/neck) sites. Microscopically, the tumour shows infiltrative growth with bland spindle cells in sweeping fascicles. There is usually prominent stromal collagen and occasional myxoid change. Small to medium sized vessels show perivascular edema. Immunohistochemistry is positive for smooth muscle actin, muscle specific actin, and nuclear beta-catenin (70%). Desmin can be focally positive.