Figure 3b. Sesamoiditis in a 21-year-old female kickboxer. (a) Coronal T1-weighted MR image shows the tibial and fibular sesamoid bones with low signal intensity (arrows). (b) Corresponding coronal STIR MR image shows the sesamoid bones with increased signal intensity (long arrows). Note the adjacent soft-tissue edema and joint effusion. Involvement of both sesamoid bones, joint effusion, and inflammatory changes in the adjacent soft tissues favor a diagnosis of sesamoiditis rather than stress response. However, the small amount of bone marrow edema within the first metatarsal head (short arrow) probably represents a stress response.