musculoskeletal and connective tissue disorders
Benign Bone Tumors and Cysts
Nonossifying fibroma (fibrous cortical defect, fibroxanthoma)
Nonossifying fibroma is a benign fibrous lesion of bone that appears as a well-defined lucent cortical lesion on x-ray. A very small nonossifying fibroma is called a fibrous cortical defect. These lesions are developmental defects in which parts of bone that normally ossify are instead filled with fibrous tissue. They commonly affect the metaphyses, and the most commonly affected sites are, in order, the distal femur, distal tibia, and proximal tibia. They can progressively enlarge and become multiloculated. Nonossifying fibromas are common among children. Most lesions eventually ossify and undergo remodeling, often resulting in dense, sclerotic areas. However, some lesions enlarge. Small nonossifying fibromas are asymptomatic. However, lesions that involve nearly 50% of the bone diameter tend to cause pain and increase the risk of pathologic fracture. Nonossifying fibromas are generally first noted incidentally on imaging studies (eg, after trauma). They typically are radiolucent, single, < 2 cm in diameter, and have an oblong lucent appearance with a well-defined sclerotic border in the cortex. They can also be multiloculated. Small nonossifying fibromas require no treatment and limited follow-up. Lesions that cause pain or are close to 50% of the bone diameter may warrant curettage and bone grafting to decrease risk of a pathologic fracture through the lesion. 