Characteristic histopathologic and radiographic findings of ECD. (A) PET and (B) ^99mTc imaging demonstrating symmetric diametaphyseal radiotracer uptake in the long bones of the legs (arrows) commonly seen in ECD patients. (C) CT and (D) MRI scans revealing sclerotic lesions of the metaphyses of femur and tibia (arrows). (E) Hematoxylin-and-eosin–stained biopsy section of ECD lesion revealing lipid-laden histiocytes characteristic of ECD. (F) Immunohistochemical stain for CD68 revealing positivity of histiocytes. CT, computed tomography; PET, positron emission tomography. See Figure 1 in the article by Diamond et al that begins on page 483