True about non-ossifying fibroma of bone -a) Present until 3rd  & 4th decadeb) Eccentricc) Prominent sclerotic margind) Histologically giant cell with areolar tissuee) Metaphyseal lesion
Non-ossifying fibroma (fibrous cortical defect)

NOF is a developmental defect in which nest of fibrous tissue appears within the bone and persists some years before ossifying. It is non-neoplasticfibrous proliferation in the metaphysis of long bones.
It is seen between 2-20 years of age and is more common in males than females.
Some lesions involute spontaneously. Other persists and gradually move towards the diaphysis as the bone grows in length.

Clinical presentation

It is asymptomatic and is almost always encountered in children as an incidental finding on x-ray.
The commonest sites are metaphysis of long bone. Most common site is distal femur in postero medial aspect.

Other sites are proximal tibia, proximal femur, both end of fibula, proximal humerus, Ribs, ilium.
X-ray features

Eccentric in location in metaphysis.
Oval radiolucent area surrounded by a thin margin of dense bone (sclerotic margin). 

​​Pathology

Although it looks cystic on x-ray, it is a solid lesion consisting of unremarkable fibrous tissue with a few scattered giant cells.
Two basic components are benign fibroblasts and osteoclast like giant cells.
Foamy pale histiocytes (macrophages), focal hemorrhage and hemosiderin pigment may also be seen.
As the bone grows the defect becomes less obvious and it eventually heals spontaenously.
However, it sometimes enlarges to several centimetres in diameter and there may be a pathological fracture.
There is no risk of malignant change.
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