Non-Ossifying Fibroma (NOF) is a non-neoplastic skeletal disorder characterized by fibrous proliferation in the metaphysis. It is also called FIBROUS CORTICAL DEFECT/ FIBROXANTHOMAS.
As per WHO, NOF is not a true neoplasm but it is a developmental disorder.
Etiology
NOF is the most common skeletal lesion approximately 30 % in the first second decade.
Trauma in the region of muscle attachment with the formation of a focal sub-periosteal hemorrhage.
Male: Female= 2:1
Site
Eccentrically located in the metaphysis of the long bone, tibia, and femur most commonly affected.
Clinical Features
Most NOF are asymptomatic and are detected incidentally
Some present with swelling, mild deformity, and with pathological fracture.
Radiological Features
It is well defined, usually oval, lytic lesion arising eccentrically on the metaphyseal cortex with a long axis parallel to the long axis of the bone.
Surrounded by a thin sclerotic rim (narrow zone of transition) which is deficient on the external side of the lesion
Typical NOF is > 2 cm in diameter and often extends to the medullary cavity.
Typical fibrous cortical defect lesion < 2cm in diameter and confined to the cortex.
Soap Bubble Appereance
Ritschl Four Stages of Non-Ossifying Fibroma
| Stage | Features |
|---|---|
| Stage A | Lesion moves towards metaphysis with bone growth and may increase in size, exhibiting more polycyclic, grape-shaped borders |
| Stage B | Involution and filling with bone tissue; mineralization tends to start in the diaphysis and proceeds toward the growthh plate |
| Stage C | Involution and filling with bone tissue; mineralization tends to start in the diaphysis and proceeds toward the growth plate |
| Stage D | Completely calcified lesion resembling a large bony islet |
Pathology
Spindle Shaped fibroblast arranged in a whorled and storiform pattern.
Histologically indistinguishable from benign fibrous histiocytoma of bone.
Treatment
NOF most are asymptomatic and detected incidentally.
If the lesion is large and lytic we need to follow up with a serial radiograph
A lesion with longitudinal extension > 22 mm and > 50 % diameter of bone has a higher risk of pathological fracture.
Symptomatic, large, non-ossifying, lower limb lesions with a high risk of pathological fracture should be treated with curettage and appropriate reconstruction.
In case of fracture; appropriate splinting and reassess after fracture healing.
See also: Enchondroma
See also: Osteosarcoma
