Characteristics

• Idiopathic bone infarcts characteristically occur in long-bone metaphyses.

• Histological testing reveals mineralisation of necrotic marrow.

• Aetiology is likely to be related to intrinsic/extrinsic vascular compromise such as thrombosis, arteritis, atherosclerosis or external compression (fractures, oedema, tumour, etc).

Clinical features

• Classically asymptomatic and discovered as an incidental diagnosis.

Radiological features

• Early rarefaction followed by sclerosis, calcification, and ossification parallel to the cortex in the healing phase.

• Bone scan – ‘cold spot’ or no increased uptake in the early stages; becomes ‘hot’ as revascularisation occurs.

Management

• No treatment is required; however, malignant fibrous histiocytoma has been reported developing in previous bone infarcts.

Bone islands

Characteristics

• Histologically these are markedly thickened bony trabeculae.

• Seen in all ages.

• Unknown aetiology but may represent a developmental anomaly.

• Usually solitary, commonest in the proximal femur and ilium.

Clinical features

• Asymptomatic – incidental diagnosis, but these are important in the differential diagnosis of more sinister lesions.

Radiological features

• Sclerotic areas within bone which are well demarcated from surrounding normal bone (narrow zone transition). Classically the margin appears feathery.

• No cortical involvement or periosteal reaction.

• Often oval with the long axis parallel to the bone.

• Bone scan – if large may show increased uptake.

Management

• Exclude more sinister pathology, but no particular treatment is required.