Osteoid osteoma

Q: What could be the presenting symptoms of this patient? show answer

A: Left lateral ankle pain, even at night and at rest.

Q: What are the x-ray characteristics of this lesion? show answer

A: Smoothly marginated cortical sclerotic thickening with a small central translucency.

Q: What is the diagnosis? show answer

A: Osteoid osteoma.

Q: What is the imaging study of choice in this type of bone lesion? show answer

A: Computed tomography.

Q: In the above case, there is a central calcification. Is this always present? show answer

A: No, central mineralisation is often absent, but when present is helpful.

Q: What is the term used for the central translucent region and what is it composed of? show answer

A: It is called a nidus and consists of a meshwork of vessels, osteoclasts, osteoid, and sometimes woven bone.

Q: What additional information can be expected from an MRI? show answer

A: MRI typically shows an inflammatory reaction (oedema and contrast enhancement), that may be very intense and involve neighbouring structures. This should not be interpreted as representing an agressive lesion.

Q: What causes inflammation in this bone lesion and how can this be exploited? show answer

A: Prostaglandine secretion, that responds well to NSAIDs. This feature may help in diagnosis and treatment.

Q: What are the most common locations for osteoid osteomas? show answer

A: Although they can be found almost anywhere, over half these lesion are found in the femur (especially proximal / neck) and mid tibia. About 11% occur in the foot and ankle region.

Q: What is the natural history of this type of bone lesion? show answer

A: There is growing evidence, that it will resolve spontaneously after an average time of 33 months.

Q: What are the treatment options? show answer

A: Traditional treatment has been surgical resection. Percutanous radiofrequency ablation under general anaesthesia is being increasingly used. Patients, who respond well to NSAIDs can also be treated conservatively.