What Is a Fibrous Cortical Defect?
The fibrous cortical defect is one of the most common benign fibrous bony lesions in children and young adolescents. It constitutes nearly five percent of all benign lesions of bone. It was first described by an American orthopedic surgeon named Phemister in 1929. It occurs in the metaphysis of long bones of skeletally immature adolescents. The most common sites of the fibrous cortical defect are the femur (thigh bone) and the distal part of the tibia (shinbone). It is mostly asymptomatic, and the lesion disappears on its own once the skeletal maturity is completed. Males are more commonly affected by fibrous cortical defects than females.
Are Fibrous Cortical Defects and Non-Ossifying Fibroma Similar?
The fibrous cortical defect and non-ossifying fibroma are the two most common benign fibrous bone lesions. Both lesions are almost similar and identical histologically; therefore, the fibrous cortical defect can also be referred to as non-ossifying fibroma. The major difference between fibrous cortical defect and non-ossifying fibroma is
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A fibrous cortical defect is a smaller variety of non-ossifying fibroma that occurs in individuals between 4 to 8 years of age. In contrast, non-ossifying fibroma is a much larger lesion than a fibrous cortical defect that affects the age group of 8 to 20.
What Causes Fibrous Cortical Defects?
The exact cause of the fibrous cortical defect is still unknown. However, some suggest that fibrous cortical defect occurs as a result of periosteal injury or due to abnormalities in the epiphyseal plate.
What Are the Symptoms of Fibrous Cortical Defect?
The fibrous cortical defect is almost always asymptomatic; however, it may undergo a pathological fracture as they grow. As a result of pathological fracture, the patient may experience some symptoms, including;
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Bone pain.
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Tenderness.
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Swelling around the affected area.
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Weakening of bone due to repeated stress fracture.
How Is a Fibrous Cortical Defect Diagnosed?
The fibrous cortical defect is mainly diagnosed through radiographic examination since it is almost always asymptomatic. In some patients, the fibrous cortical defect may exhibit some symptoms due to a pathologic fracture of bone which may help the doctor diagnose the condition. The doctor will suggest imaging tests for a more definitive diagnosis of the fibrous cortical defect.
X-ray :
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In an X-ray image, the fibrous cortical defect depicts a well-defined oval, radiolucent cystic lesion located in the cortical layer of a bone with a thin sclerotic rim outlining the cyst. The size of the cystic lesion is always less than 3 cm. Fibrous cortical defect neither shows any involvement of the underlying medullary cavity (part of the bone that contains bone marrow) nor any periosteal reaction (a radiographic finding that indicates new bone formation in response to injury of the periosteum).
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The radiographic features may slightly differ if the fibrous cortical defect grows and becomes non-ossifying fibroma (bone lesions greater than 3 cm in diameter). The X-ray image of the non-ossifying fibroma shows a large cystic lesion with a thin sclerotic rim that protrudes into the medullary cavity.
MRI (Magnetic Resonance Imaging) :
MRI is usually not indicated in the diagnosis of the fibrous cortical defect. However, it may be suggested if the fibrous cortical defect fails to exhibit its characteristic radiographic features in X-rays. In MRI, strong magnetic fields and radio waves are used to generate detailed anatomic images. There are two different contrast images produced by MRI: T1 and T2 weighted images. These images depict differences in signals based on the relaxation time of various tissues. The signal characteristics of the fibrous cortical defect in MRI include;
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T1 - Low signal intensity.
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T2 - The signal intensity may vary depending on the phase of healing.
CT (Computed Tomography) Scan:
CT scan provides cross-sectional images of the cyst using multiple low-dose X-rays. The radiographic features of Fibrous cortical defect in CT scans are similar to the X-rays.
What Are the Different Stages of Fibrous Cortical Defect or Non-ossifying Fibroma?
The different stages of fibrous cortical defect or non-ossifying fibroma are categorized based on Ritschl's classification. Ritschl et al. classification is based on the lesion location and morphological characteristics of the fibrous cortical defect and non-ossifying fibroma depicted on radiographic images. Ritschl's classification consists of four stages, out of which stage A is considered to be the fibrous cortical defect, and the rest of the stages depicts non-ossifying fibroma”.
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Stage A: It describes a small oval radiolucent cystic lesion with smooth outlines.
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Stage B: It describes a radiolucent cystic lesion with polycyclic borders.
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Stage C: It describes a partially calcified lesion.
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Stage D: It describes a completely sclerotic lesion.
How Is Fibrous Cortical Defect Treated?
No treatment is typically required for fibrous cortical defects since they are benign, asymptomatic, and self-limiting. However, as the cyst grows and expands, it leads to a pathological fracture of the bone. The treatment for cases with pathological fracture includes;
1. Immobilization:
The affected bone is immobilized by placing a cast, splint, or brace on the bone. In this procedure, the surgeon first surgically aligns the broken bone fragments and then places a custom-made cast, braces, or splints on the bone to rejoin the fragments through natural healing.
2. Curettage:
Curettage refers to the surgical scraping of the bone, which is done to remove the cystic lesion completely. In curettage, the surgeon makes an incision in the bone and creates a window. The cystic fluid is then aspirated, and the tissue lining is curetted. After curettage, the surgeon packs the remaining cavity with an allogeneic bone graft (bone graft received from a donor), autogenous bone graft (bone graft obtained from another part of the patient's body), or bone chips.
Which Syndrome Is Associated With Fibrous Cortical Defect?
The syndrome associated with the fibrous cortical defect is Jaffe-Campanacci syndrome. Jaffe-Campanacci syndrome is a disorder characterized by the following;
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Multiple fibrous cortical defects of the long bones and jaw.
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Cafe au lait spots (light to dark brown pigmentation).
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Intellectual disability.
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Kyphoscoliosis (deviation of the spine's normal curvature on both the coronal and sagittal plane).
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Hypogonadism (a condition in which the sex glands produce little or no sex hormones) or cryptorchidism (a birth defect in which the testes fail to descend into the scrotum from the abdomen).
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Ocular malformations (abnormalities of eye).
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Giant cell granuloma of the jaw (benign tumor of the jaw).
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Axillary and inguinal freckling (a condition in which freckles are present in the armpits or the groin area).
What Are the Differential Diagnosis of Fibrous Cortical Defects?
The differential diagnosis of fibrous cortical defect includes;
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Non-ossifying fibroma: A benign bone tumor.
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Osteomyelitis: An inflammation of the bone caused by a bacterial or fungal infection.
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Intracortical Osteosarcoma: A rare type of osteosarcoma that arises within the cortex of the bone.
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Cortical Desmoid: A self-limiting fibro-osseous lesion that mostly occurs in the posteromedial aspect of the distal femur.
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Osteoid Osteoma: A benign bone tumor that develops in the long bones.
Conclusion:
Fibrous cortical defects are mostly evident on X-rays, but if it grows and transitions into non-ossifying fibroma, additional imaging tests may be required. It is almost always asymptomatic and does not require any treatment. However, if the fibrous cortical defect is associated with any pathological fracture, immobilization of fractured bone with casts or braces is done.
