Figure 4a. Myelodysplastic syndrome in a 43-year-old woman with ankle pain. (a) Lateral ankle radiograph shows a poorly defined region of lucency (arrowheads) centrally within the distal tibia. (b) Sagittal T1-weighted MR image shows a curvilinear band of low signal intensity (arrowhead) that surrounds a central region of fat signal intensity (*). (c) Sagittal T2-weighted fat-suppressed MR image shows a high-signal-intensity curvilinear band that surrounds a low-signal-intensity central region of necrotic bone. Note the double line sign (arrow), a feature that is virtually pathognomonic of osteonecrosis. Images from 2%–3% of patients referred to the Orthopaedic Oncology Clinic showed findings characteristic of osteonecrosis but interpreted as potential malignancy. MR imaging should allow a confident diagnosis in most cases.