non-ossifying fibroma
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Definition: Nonossifying fibroma is a benign, lytic lesion of fibrous origin most often observed in the metaphyseal region of the long bones in children and adolescents. It is frequently asymptomatic and is often characterized by a history of spontaneous resolution.
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.
The predominant element is a spindle cell of fibroblastic appearance. There are also irregularly scattered osteoclasts.
Synopsis
eccentric, sharply delineated, metaphyseal lesion in long bones of adolescents
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
Microscopy
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.
Associations
adamantinomas of long bones
Sometimes accompanied by epiphyseal disorders
Pathogenesis
Controversy regarding whether neoplastic or developmental aberration at epiphyseal plate.
Radiography
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. Scintigraphy may show increased activity depending on the stage of healing. 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.
Lesions persisting in older children which are more than 2 cm in size have been termed nonossifying 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. Also, see Campanaccis syndrome.
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.
Pathological synopsis
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
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.