Non -Ossifying Fibroma - Fibrous Cortical Defect

Non-ossifying fibroma (NOF) is a well circumscribed, solitary fibrous proliferation. This lesion is found mostly in children with 75% occurring in the second decade. The lesion is found in males more commonly than in females and may occur in as many as 35% of all children.' It is a non-neoplastic process that occurs in the juxtaepiphyseal region of the long bones. The most common site is the femur followed by the tibia .
Clinically, non-ossifying fibromas are asymptomatic and are usually discovered as an incidental finding on x-ray. Occasionally, a larger lesion presents as a pathologic fracture. The classic scenario is a child who has a minor injury in a sports contest and a plain radiograph is taken in a local emergency room.  A lesion is seen and the child is referred to an orthopaedic surgeon for evaluation.  Generally, a careful history and physical examination will show that the child's pain is related to the nearby joint rather than the lesion, and that the pattern of the symptoms fits that which is expected in a sprain or strain injury.  If there was pain before the injury that seems to arise from the lesion, the diagnosis of NOF is highly suspect. Jaffe-Campanacci syndrome is a constellation of symptoms including multiple non-ossifying fibromas, cafe-au-lait spots, mental retardation, hypogonadism, ocular and cardiovascular abnormalities.
Non-ossifying fibromas have a very typical appearance on x-ray. They are eccentric, multi-loculated sub-cortical lesions with a central lucency and a scalloped sclerotic margin. There is sometimes cortical thinning but no periosteal reaction. Serial x-rays will show the lesion migrating away  from the epiphyseal plate with time.  If the lesion is not eccentric, has no sclerotic rim, or is not multi-loculated, the diagnosis of  NOF is suspect and further evaluation is warranted.  Since these lesions may be treated by observation only without biopsy, the physician should be quite certain of the diagnosis before formulating a treatment plan.  If any doubt exists, the advice of an orthopaedic oncology specialist should be sought. 
On gross appearance, non-ossifying fibromas have a yellow-brown color and have a fibrous consistency. Microscopically, dense fibroblasts are found in whorled and storiforrn patterns. Xanthoma cells are present as well. There is no pleomorphism or atypia among the spindle cells and there are very few mitoses.
These lesions normally regress spontaneously. The only definite indication to treat non-ossifying fibromas is a pathologic fracture. The natural history of these lesions is that they either spontaneously resolve or move to the diaphysis of the bone.

Bullough, Peter, Orthopaedic Patholovv (third edition), Times Mirror International Publishers Limited: London. 1997.
Huvos, Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.
Kurnar, R. et al., Fibrous Lesions of Bones, Radiographics, 10:237-256, 1990.
Marks, KE and TW Bauer, Fibrous Tumors of Bone, Orthopaedic Clinics of North America, 20(3): July, 1989.
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