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non-ossifying fibroma

Wednesday 8 September 2004

Definition: Non-ossifying fibroma is a benign, lytic lesion of fibrous origin most often observed in the metaphyseal region of the long bones in children and adolescents.

Non-ossifying fibrom is frequently asymptomatic and is often characterized by a history of spontaneous resolution.

Radiologic surveys have shown a 35% incidence of NOF in normal children.

Most clinical cases are detected as incidental findings on imaging studies, although occasionally a pathologic fracture through a large lesion causes the patient to seek medical attention.

The lesions range in size from a few millimeters to several centimeters and are characterized by their cortical, eccentric location, as well as by their well-demarcated central lucency surrounded by scalloped sclerotic margins. Often, an NOF is elongated in the longitudinal axis of the bone.

Serial radiographs have demonstrated the migration of the defect away from the epiphyseal plate with time. As the lesions regress, the affected area often shows residual sclerosis.

The lesion typically arises in the metaphyses of long bones particularly the distal femur and tibia. It is common, possibly affecting more than 40% of boys and 30% of girls.

The lesion is thought to originate at the insertion site of a ligament or tendon and it has been suggested that it may reflect a previous traction injury.

Although the lesion arises in the metaphyseal region it may migrate towards the diaphysis with growth. The lesions are usually asymptomatic, although they are occasionally associated with pathological fractures.

Synopsis

- eccentric, sharply delineated, metaphyseal lesion in long bones of adolescents
- occurs mainly in adolescents
- metaphyseal fibrous defect of lower end of tibia withsharp delineation and sclerotic margins
- few or no symptoms except pain
- usually found incidentally on radiography
- fractures can occur through the thinned cortex
- usually long tubular bones, particularly upper or lower tibia and lower femur
- granular and brown or dark red
- eccentric
- sharply delimited
- sclerotic margins
- not too distant from epiphysis

Macroscopy

Gross inspection of surgical curettings reveal fragments of soft, somewhat friable red-brown tissue with foci of yellow discoloration.

- irregular thinning of the cortical bone
- underlying mahogany brown lesional tissue
- scalloped margin of the lesion
- cortical thinning
- The reddish brown color is typical.
- The focal areas of gray can represent fibrous tissue.
- The areas of yellow discoloration can be foamy cell accumulation.

Microscopy

The predominant element is a spindle cell of fibroblastic appearance. There are also irregularly scattered osteoclasts.

The microscopic findings include a cellular tissue of unremarkable fibrohistiocytic spindle cells arranged in an interlacing, whorled pattern and interspersed with multinucleated giant cells and islands of pale foamy histiocytes.

Hemosiderin deposits and scattered lymphocytes are characteristic features.

- cellular masses of fibrous tissue

  • often storiform pattern
  • The predominant element is a spindle cell of fibroblastic appearance.
  • irregularly scattered osteoclasts.
  • collections of foamy and hemosiderin-laden macrophages
  • Exceptionally, bizarre nuclear features: not necessarily indicative of malignant nature.

Nota bene: When loose and with an intramedullary component, designated non-ossifying or non-osteogenic fibroma, rather than metaphyseal fibrous defect.

Nota bene: Microscopic appearance reminiscent of benign fibrous histiocytoma: designated as such by some, especially when in adult in place other than metaphyses of long bones.

Adult NOF

Although the vast majority of cases of NOF occur in children, very rarely lesions that are histologically indistinguishable from them may be seen in adults, where they are usually reported as "benign fibrous histiocytoma" or "fibroxanthoma".

On imaging studies, these adult lesions differ from those seen in children by having less distinct borders and being central rather than eccentric.

They may either be lucent or sclerotic, and the bones involved are likely to be different from those seen in children with flat bones more commonly involved in adults.

Patients may experience mild pain or they may be asymptomatic.

On microscopic examination, however, just as in childhood lesions, the spindle cell stroma has a whorled or ‘storiform’ pattern.

The predominant fibrohistiocytic cells are mixed with polygonal histiocytic cells, which have a more vacuolated cytoplasm and may be filled with lipid, hemosiderin deposits, multinucleated giant cells, and sparse chronic inflammatory cells are also evident.

Differential diagnosis

The microscopic features may on occasion cause diagnostic confusion with other giant cell containing lesions, more especially giant cell reparative granuloma (GCRG). However, the clinical and radiographic presentation of NOF is so typical that it should rarely be confused with anything else.

Differential diagnosis:

- giant cell tumor of bone
- benign fibrous histiocytoma
- malignant fibrous histiocytoma (MFH)
- aneurysmal bone cyst
- chondroblastoma
- fibrous dysplasia of bone
- foamy cells

  • xanthogranuloma
  • end stage of an eosinophilic granuloma (Langerhans cell histiocytosis)

- desmoid fibromatosis

  • parosteal desmoid fibromatosis
  • juxtacortical desmoid fibromatosis

Associations

- adamantinomas of long bones
- Sometimes accompanied by epiphyseal disorders

Pathogenesis

- Controversy regarding whether neoplastic or developmental aberration at epiphyseal plate.

Radiography

- eccentric lucent lesion with thinned cortex
- may have a multilocular appearance
- often have a sclerotic margin
- cortical erosion
- thin layer of periosteal bone covering the expanded tumor.

Radiography show an eccentric lucent lesion with thinned cortex, which may have a multilocular appearance and often a sclerotic margin.

The lesions spontaneously regress with time; radiographs will show increasing marginal sclerosis followed by progressive ossification of the lesion extending from its diaphyseal aspect.

The appearance on conventional radiographs should be characteristic and no further imaging is indicated.

Aggressive malignancies tend to have less well defined borders, and more periosteal reactions, resulting in a large, less sharply defined transition zone between the lesion and normal bone

However, the lesions are commonly seen as incidental findings on other imaging.

Lesions persisting in older children which are more than 2 cm in size have been termed non-ossifying fibromas but appear to represent the same histological entity.

They often extend into the medullary cavity and are associated with an increased risk of pathological fracture due to their size.

CT

CT scan should not be performed unless a strong doubt about diagnosis is present, except to confirm a pathological fracture (see Image).

This lesion is located eccentrically and CT scan should depict a central lucency. CT scan may confirm a minimally displaced fracture.
This scan could help in preoperative planning in FCDs in rare locations like femoral neck.

Bone scan

This study is not indicated for diagnosis. Nevertheless, in some cases, a methylene diphosphonate (MDP) technetium bone scan could help to appreciate biological activity of lesion.

A minimal increased uptake can be seen as depicted in rni image. In associated fractures, this study is not useful.

Scintigraphy may show increased activity depending on the stage of healing.

MR imaging

Likewise MR imaging may show variable signal intensity depending the lesion’s stage of healing. There is often central decreased T2-weighted signal due to collagen and haeomosiderin deposition.

Cytogenetics

- translocation (1;4)(p31;q34) (#12699892#)
- del(4)(p14) (#8330278#)

Treatment

Treatment is usually unnecessary because healing occurs spontaneously over a period of several years. If a pathological fracture occurs across an exceptionally large lesion then curettage and bone grafting is required.

This kind of tumor is neither malignant, nor aggressive, so the primary reason to treat it is to avoid a fracture, especially in athletic children. In some cases, a non-ossifying fibroma may require no treatment at all, because this condition resolves on its own over time.

However, your child’s orthopaedic surgeon may decide that an operation is warranted if a fracture has occurred or the tumor is weakening the bone, putting it at significant risk of a fracture. This may be a very difficult decision for the parents and the surgeon.

The risks of surgery and the healing and rehabilitation time must be balanced against the desire to play sports and avoid fracture. There is no right or wrong answer and the decision needs to be individualized to the child.

If an operation is recommended, the procedure of choice is usually curettage and bone grafting. Curettage is an operation during which the tumor is scraped out of the bone with a special instrument called a curette that has a scoop, loop or ring at its tip. For this procedure, surgeons make an incision in the bone to create a window.

The tumor is completely curetted and the remaining cavity is then packed with donor bone tissue (allograft), bone chips taken from another bone (autograft), or other materials depending on the preference of the surgeon. The patient is usually placed in a cast or brace for six weeks and then can undergo protected weight bearing for another six weeks. It usually takes 3-6 months before a child can return to contact sports.

If a fracture is involved, the operation is put off until the fracture heals with cast immobilization followed by a period observation after it has healed. In major long bones, such as the femur, internal fixation (surgically placed metal rods and pins to fix a broken bone) may be necessary. At times, during the healing process, the tumor may heal as well.

Prognosis

Although every patient is different, the long-term outlook for a patient with a non-ossifying fibroma is generally excellent. These tumors, as a rule, resolve on their own, usually at skeletal maturity. The concern lies in whether they will cause a fracture while active. Recurrence is rare.

Links

- emedicine.medscape.com
- e-radiography.net
- pathconsultddx

References

- Arata MA, Peterson HA, Dahlin DC. Pathological fractures through non-ossifying fibromas. Review of the Mayo Clinic experience. J Bone Joint Surg (Am). 1981;63:980–988.

- Cunningham JB, Ackerman LV. Metaphyseal fibrous defects. J Bone Joint Surg (Am). 1956;38:797–808.

- Craver RD, Heinrich S, Mirra J. Fibrous cortical defect with bizarre nuclear features. Ann Diagn Pathol. 1997;1:26–30.

- Clarke BE, Xipell JM, Thomas DP. Benign fibrous histiocytoma of bone. Am J Surg Pathol. 1985;9:806–815.

Portfolio

  • Non-ossifying fibroma (eMedicine)
  • Fibrous cortical defect or non-ossifying fibroma (eMedicine)
  • Multiple fibrous cortical defects
  • Non-ossifying fibroma