Osteoid osteoma

Case contributed by James R Riesing

Presentation

Edema on the right proximal tibia with tenderness on palpation.

Patient Data

Age: 17 years
Gender: Male
x_ray

AP and lateral views of the right lower leg display a broad, cortically based lesion on the medial, proximal tibia. 

mri

An axial STIR image through the lesion showed a focal, fusiform periosteal thickening with a 3mm nidus in the superficial cortex. There is additional adjacent sclerosis and hyperintense T2/STIR marrow signal.

ct

Axial CT demonstrated a round lucency with 3 mm sclerotic nidus in the proximal, medial tibial metadiaphyseal cortex. There is corresponding periosteal reaction and cortical thickening. 

Radiofrequency Ablation

ct

The image shows a CT guided radio frequency ablation using a 10 mm Osteocool RFA ablation probe.

3 months later

mri

Post ablation changes are visible 3 months following radio frequency ablation. Central nidus is now absent and there is T2 hyper intensity in the bone marrow surrounding RFA site.

Case Discussion

An osteoid osteoma is a common, benign bone lesion that is prototypically painful at night with pain relieved by NSAIDs. Imaging will reveal a cortical nidus with surrounding bone marrow and periosteal changes. The nidus may or may not have a small area of central sclerosis. 

NSAIDs are considered first-line treatment, but there are numerous risks associated with prolonged use. Due to this, radiofrequency ablation is often the treatment of choice. Though RFA is highly effective, more than one ablation may be necessary due to a small risk of recurrence.

In this case, follow-up imaging was attained due to concern for bone stress injuries. This allowed excellent visualization of the expected post-RFA changes. The central nidus was absent and there is circumferential sclerosis at the ablation site representing successful treatment. 

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