Non-ossifying fibroma is a cortically based benign lesion of bone wherein the normal bone has failed to form during skeletal growth and the area instead contains fibrous tissue. Non-ossifying fibroma goes by many names which will be used synonymously here; fibrous cortical defect, fibroxanthoma, metaphyseal fibrous defect and non-osteogenic fibroma.
The most common presentation for non-ossifying fibroma is as an incidental finding. A radiograph is taken for injury to an area (often the knee or ankle) and lesion is discovered. Careful history and physical examination can localize the pain to another cause almost universally.
In cases with very large lesions in weight bearing bones, the lesions can present as gradual onset pain which is exacerbated by activity. The pain is relieved by rest or weight bearing restriction. In these cases the pain represents an impending pathologic fracture (abnormal bone failing under physiologic stresses) and should be managed as such either with bracing/casting or surgically.
Beware two lesions in the same bone. Osteosarcoma and Giant Cell Tumor have been described arising immediately adjacent to the fibrous cortical defect.
Non-ossifying fibroma can be expansile, but expansile lesions should broaden the differential when seen.
Multiple non-ossifying fibromas can indicate the presence of Jaffe-Campanacci syndrome which can have the following findings:
Multiple giant NOF
Other irregular pigmentations
Occular and cardiovascular abnormalities
Non-ossifying fibroma can be present in up to 30% of children. As mentioned previously the most common presentation is as an incidental finding. There are multiple lesions in up to 8% of cases when a syndrome is not present.
Pathology and pathophysiology
The gross pathology is soft tan fibrous tissue. Microscopically, there are spindled fibroblasts in a dense collagen background. Scattered ossification, foamy lipid laden macrophages and rare mononuclear giant cells can be seen.
The lesions typically undergo spontaneous involution as the skeleton matures. The fibrous tissue is replaced by bone and the cortex is remodelled to normal architecture. Often the oldest parts of the lesions (away from the physis) can have mineralization exceeding the more immature portion of the lesion.
The differential diagnosis contains the following:
- Brown tumor of hyperparathryoidism
- Paget's disease
- Fibromatosis of bone (desmoplastic fibroma)
- Osteofibrous dysplasia
The radiographic characteristics and the location can often narrow the differential diagnosis substantially.
The exact cause is unknown, but the age and location distribution implicate the growing physis as the affected mechanism. The involution pattern also speaks to this mechanism with areas more distant from the adjacent physis ossifying before areas closer to the physis.
Radiographic and laboratory findings
Radiographic findings are a well marginated, sclerotic boarded eccentric metaphyseal lesion with a fibrous matrix. The distal femur and proximal tibia are the most common sites. The distal tibia is often affected as well. A lesion with these features in the anterior tibial diaphysis could be osteofibrous dysplasia and this lesion should be considered in the differential diagnosis. Large lesions can have pathologic fractures or angular deformity associated with them.
CT scan will show intact cortices with thinning.
MRI will show intermediate signal on fat and fluid sensitive sequences characteristic of fibrous tissue.
Risk factors and prevention
There are no particular risk factors for development of a solitary lesion.
The natural history of the lesion is spontaneous resolution with no symptoms. Serial radiographic imaging is adequate treatment for small, asymptomatic lesions. Biopsy should be reserved for cases in which the diagnosis is in question due to temporal course or when surgery is planned to treat impending or completed pathologic fracture.
Surgery is typically an intralesional procedure with bone grafting. Internal fixation or post operative casting can be used to stabilize defects or fracture until healing.
Outcomes are excellent with no sequelae in the vast majority of cases. In cases of pathologic fracture, complications associated with the fracture (physeal disturbance, angular deformity etc.) are the only potential complications.
Children with benign lesions rarely need any ancillary support. Recognize that simply visiting an oncologist can be very stressful for the patients’ parents and reassurance of the diagnosis is paramount.
Cortical desmoid tumor is a specifc lesion of this type seen in the posteromedial distal femur at the origin of the medial head of the gastrocnemius muscle.
Non-ossifying fibroma, fibrous cortical defect, fibroxanthoma, Jaffe-Campanacci syndrome, cortical desmoids tumor, soap bubble, ground glass, eccentric.
Skills and competencies
A medical student should be able to recognize and describe the lesion radiographically as diagnosis on plain radiograph is the single essential skill needed to manage this lesion.
. _In: OrthopaedicsOne - The Orthopaedic Knowledge Network. Created
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