Fact-sheet: Osteoid osteoma


Updated on 10/20/2023 at 11:06 AM

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Definition

Common benign tumor:
- 4% of primary bone tumors
- 15% of benign bone tumors

Mainly affects children and young adults (peak frequency between 7 and 25 years).

Slight male predominance (sex ratio 2-3/1).

Typical locations:
- long bones in 70 to 80% of cases (femur and tibia in 60% of cases)
- posterior vertebral arch.

Several types: cortical, intramedullary, subperiosteal, or intra-articular.

Clinical features

Insomnia-causing nocturnal pain relieved by aspirin.

Radiography

Typical cortical form

Nidus = cortical lucency less than 15 mm, with possible central calcification not always visible on plain radiographs.

Reactive cortical thickening secondary to periosteal apposition (except for intra-articular osteoid osteoma).

CT

Same imaging features as on radiographs; CT is useful to identify the nidus if not visible on radiographs.

Typical cortical form

Round shape on axial images and oval on coronal/sagittal images, with a maximum/minimum diameter ratio < 2.5

Well-defined margins

Central calcification

Circumferential radiolucent rim

Peripheral sclerosis with ill-defined margins 1A1

Feeding vessel sign

MRI

Typical cortical form

Nidus: T2 hyperintense, T1 iso- to hypointense.

Cortical thickening hypointense on all sequences.

Intense marrow edema centered on the nidus, falsely worrisome.

Indications: - atypical appearance on radiographs/CT - dynamic sequences are useful to identify the nidus = arterial enhancement with rapid, partial wash-out

Management

Percutaneous treatments: laser photocoagulation, radiofrequency ablation, cryotherapy

Medical treatment: bisphosphonates

Surgical excision: invasive, used when percutaneous treatment is contraindicated (difficult access, proximity to neurovascular structures).

Differential diagnosis

Osteoblastoma: larger, involves the spine and flat bones, with milder adjacent bone sclerosis.

Stress fracture: linear.

Cortical osteitis: poorly defined, laminated osteolysis, soft tissue collection.