Intercostal muscle contraction or rib bone marrow activity?: Look for ancillary clues

Diffuse and uniform FDG uptake in the ribs and the intercostal muscles might appear similar on FDG-PET images and a reliable differentiation between the two is important for accurately identifying the underlying process. The former usually suggests excessive contraction of intercostal muscles mostly due to chronic obstructive pulmonary disease, whereas the latter signifies either bone marrow stimulation or involvement by a pathologic process. At times, images may appear confusing and may be misinterpreted. However, in both clinical settings, there are additional ancillary signs, which are helpful in making a correct diagnosis. We herein present 2 case vignettes from each category in which other ancillary signs helped to distinguish FDG rib uptake from intercostal muscle uptake.