What is Periosteal reaction? it`s types? And how it is helpful in diagnosis.

Periosteal reaction:
A periosteal reaction is a non-specific reaction and will occur whenever the periosteum is irritated by a malignant tumor, benign tumor, infection or trauma.
There are two patterns of periosteal reaction: a benign and an aggressive type.
The benign type is seen in benign lesions such as benign tumors and following trauma.
An aggressive type is seen in malignant tumors, but also in benign lesions with aggressive behavior, such as infections and eosinophilic granuloma.

Benign periosteal reaction
Detecting a benign periosteal reaction may be very helpful, since malignant lesions never cause a benign periosteal reaction.
A benign type of periosteal reaction is a thick, wavy and uniform callus formation resulting from chronic irritation.
In the case of benign, slowly growing lesions, the periosteum has time to lay down thick new bone and remodel it into a more normal-appearing cortex.

Aggressive periosteal reaction
This type of periostitis is multilayered, lamellated or demonstrates bone formation perpendicular to the cortical bone.
It may be spiculated and interrupted - sometimes there is a Codman's triangle.
A Codman's triangle refers to an elevation of the periosteum away from the cortex, forming an angle where the elevated periosteum and bone come together.
In aggressive periostitis the periosteum does not have time to consolidate.



In these X-Rays:

* left:
Osteosarcoma with interrupted periosteal rection and Codman's triangle proximally.
There is periosteal bone formation perpendicular to the cortical bone and extensive bony matrix formation by the tumor itself.
* middle:
Ewing sarcoma with lamellated and focally interrupted periosteal reaction. (blue arrows)
* right:
Infection with a multilayered periosteal reaction.
Notice that the periostitis is aggressive, but not as aggressive as in the other two cases.

Note that: Fibrous dysplasia, Enchondroma, NOF and SBC are common bone lesions.
They will not present with a periosteal reaction unless there is a fracture.
If no fracture is present, these bone tumors can be excluded.
So, Periosteal reaction excludes the diagnosis of Fibrous dysplasia, Enchondroma, NOF and SBC unless there is a fracture