Fibrous cortical defects (FCDs) are common, generally harmless bone lesions that frequently appear in children. These non-cancerous growths are often discovered by chance during X-rays performed for unrelated reasons. While their detection can sometimes cause concern, FCDs typically do not pose a serious health risk.
Understanding Fibrous Cortical Defects
A fibrous cortical defect is a benign lesion found in the outer layer (cortex) of long bones, often near the growth plate. These defects are characterized by a localized area where normal bone tissue is replaced by fibrous tissue. Larger FCDs (over 2-3 cm) are often called non-ossifying fibromas (NOFs), but are biologically similar.
FCDs commonly appear as well-defined, translucent areas on X-ray images, sometimes with a clear, dense border. They are most frequently located around the knee, though they can appear in other long bones. These lesions are remarkably common, present in up to 30-40% of skeletally immature children and adolescents, often resolving spontaneously over time.
Is It a Cause for Concern?
Fibrous cortical defects are typically asymptomatic, causing no pain or noticeable symptoms. Most FCDs resolve on their own as a child grows. FCDs do not transform into cancer.
While generally harmless, rare instances might warrant closer medical attention. Larger lesions, especially non-ossifying fibromas, might occasionally cause mild pain or increase the risk of a pathological fracture (a break in a weakened bone area). This risk increases if the lesion is very large, exceeding 50% of the bone’s diameter. In extremely rare cases, multiple FCDs can be associated with Jaffe-Campanacci syndrome, a genetic condition. However, these situations are uncommon, and even when a fracture occurs, it is usually managed conservatively.
How It’s Discovered and Tracked
Fibrous cortical defects are almost always discovered incidentally. They are found by chance during an X-ray for an unrelated reason. The characteristic appearance of an FCD on a plain X-ray is often sufficient for diagnosis.
Advanced imaging techniques like MRI or CT scans are rarely necessary for confirming an FCD diagnosis. These might be used if initial X-ray findings are unclear, if there are atypical symptoms, or if there is a suspicion of complications. For typical FCDs, observation is usually recommended, sometimes with a follow-up X-ray to monitor resolution or stability.
What to Expect After Diagnosis
After a diagnosis of a fibrous cortical defect, most individuals can expect a positive long-term outlook. The majority of FCDs require no specific medical treatment. They tend to disappear spontaneously as the child reaches skeletal maturity.
Once diagnosed and confirmed as a benign FCD, the lesion is unlikely to cause any future symptoms or complications. Children and adolescents with FCDs can typically continue with their normal activities without restriction.