Fig. 5.

a, b, c, d Primary. A 53-year-old male patient with pain, swelling, and stiffness of the left knee. STIR imaging from the first MRI exam (a, b) highlights edema (A single asterisk (*) in a and arrowheads in b) in the medial condyle; degenerative phenomena affecting meniscuses, articular cartilage and ligaments are not present. STIR imaging performed after two months (c, d) shows that edema (*), from the medial compartment of the knee, has moved into the lateral compartment of the same knee, while all the other findings observed at the first examination remained unchanged. Every possible etiology has been excluded: this is an example of migratory primary ELMSI