Imaging of Musculoskeletal Disorders Bone tumours - Primary
Key points
Benign and malignant bone lesions are not always distinguishable with imaging
Lesions are described as having aggressive or non-aggressive features
Aggressive features can be similar to the changes seen in osteomyelitis
Imaging techniques cannot always distinguish between malignant tumours and other aggressive lesions of bone, such as osteomyelitis. Therefore, the terms ‘benign’ and ‘malignant’ are best avoided when describing possible bone tumours. Rather, the terms ‘aggressive lesion’ and ‘non-aggressive lesion’ are frequently used to describe imaging features of suspected bone tumours.
Features which would favour an aggressive lesion, such as cancer or infection, include a wide ‘zone of transition’ and 'periosteal reaction'.
Zone of transition
The zone of transition is the point at which normal bone can be distinguished from abnormal bone.
The bone texture is very abnormal distally – the normal trabecular pattern is replaced by small irregularly-shaped holes
The term ‘moth-eaten’ is often used to describe this type of abnormal bone texture
The bone texture appears normal more proximally
It is not possible to define a point at which normal bone becomes abnormal – the ‘zone of transition’ is wide
Biopsy proved this bone lesion to be a primary osteosarcoma
(Same patient as image below)
Periosteal reaction
The periosteum reacts to the presence of aggressive bone lesions by laying down abnormal new bone. The presence of ‘sunburst’ periosteal reaction (irregular frond-like thickening of the cortex), or a ‘Codman’s triangle’ (thickened cortex lifting away from the bone) are features associated with high likelihood of a primary bone malignancy.
