Bone tumours

Checklist - Periosteal Reactions

Step 6. Periosteal Reactions

The periosteum is the outermost layer of the bone and contains osteoid-producing cells (osteoblasts). Normally, the periosteum is radiolucent and not visible on x-ray. However, when mineralisation occurs through the action of the osteoblasts, as a result of a local benign/paraosseous process, the periosteum will be visible; this is known as a periosteal reaction.
The speed of mineralisation partly depends on the age of the patient. The younger the patient, the faster the mineralisation of the periosteum and the more quickly it will become visible on x-ray. 
If blood, pus or tumour tissue comes between the periosteum and the cortex, this can lead to elevation of the periosteum and periosteal stimulation, causing mineralisation to occur. A periosteal reaction can therefore have various causes, including trauma, infection and neoplasm. There are also different types of periosteal reaction. The type of periosteal reaction can provide information about the aggressiveness and speed of growth of the bone lesion, which can ultimately help in the process of differential diagnosis.  
The following periosteal reactions will be discussed in brief: expansive (ballooning), solid, single layer, multilayer, hair-on-end and the Codman’s triangle.