Fig. 8

Osteoid osteoma versus osteomyelitis. (a–d) Male, 15 years old, presenting with knee pain for 2 months. MRI T2 FS (a), T1 (b), T1 FSGD (c) and CT (d) showed a nidus with smooth margins (arrows), a central mineralized portion (dashed arrows), homogeneous gadolinium enhancement (dotted arrows) and hazy T1 bone marrow edema around the lesion (asterisk). (e–h) Male, 13 years old, presenting with knee pain for 6 weeks. MRI T2 FS (e), T1 (f), T1 FS GD (g) and CT (h) showed a bone abscess with irregular margins and peripheral enhancement (arrows). Note there was mild bone marrow edema (asterisk), a positive penumbra sign (dashed arrow in f) and a small peripheral bone sequestrum (curved arrow in h)