Osteoid osteoma of the distal tibia

Initial radiograph shows well-defined subcentimeter lytic bone lesion in the distal tibia metaphysis (see annotated images below). Though subtle and initially uncommented upon, there is smooth periosteal and cortical thickening of the posterior tibial metaphysis noted on the lateral images.

On the zoomed frontal images, the lytic lesion is highlighted in green. On the zoomed lateral images, the periosteal and cortical thickening are highlighted in green (compare with the normal cortex in blue which tapers in thickness from diaphysis to epiphysis.)

Selected images from an ankle MRI show a heterogenous, enhancing, cortically-based lesion in the posterolateral distal tibial metaphysis. There is adjacent bony sclerosis as suggested by hyposignal in the medullary cavity on T1WI pre-contrast images.  There is enhancement in the adjacent bone, periosteum (which is smoothly thickened) and even soft tissues. Osteoid osteoma is the most likely diagnosis, but CT can help better delineate a nidus.

CT confirms an approximately 5 mm lytic nidus with central punctate calcification surrounded by sclerotic trabecular, cortical and periosteal reaction. 3D reconstructions depict the undulated, smooth periosteal thickening.

Incidentally, posteromedially to this lesion, there is a sclerotic focus of bone most likely representing an enostosis (bone island).