Fibrous cortical defect described on X-ray as Small, often multilocular, eccentric lucency that causes cortical thinning and expansion and is sharply demarcated by a thin, scalloped rim of sclerosis. Initially round, the defect soon becomes oval with its long axis parallel to that of the host bone.
NOTES:Fibrous cortical defect is not a true neoplasm, but rather a benign and asymptomatic small focus of cellular fibrous tissue causing an osteolytic lesion in the metaphyseal cortex of a long bone (most frequently the distal femur). One or more fibrous cortical defects develop in up to 40% of all healthy children. Most regress spontaneously and disappear by the time of epiphyseal closure. A persistent and growing lesion is termed nonossifying fibroma .
Fibrous cortical defect: Multilocular, eccentric lucency in the distal tibia. Note the thin, scalloped rim of sclerosis.