Fibrous Cortical Defect and Non-ossifying Fibroma Imaging

Introduction

Fibrous cortical defects are small (less than three centimeters), non-aggressive, asymptomatic, eccentric cortical defects that usually disappear; however, sometimes, they increase in size and develop into fibroxanthoma. Non-ossifying fibroma is eccentric, larger (more than three centimeters), intramedullary lesions that form a superficial and scalloped pattern in the nearby cortex.

Nonetheless, regarding size and natural history, NOF and FCD are regarded as two different lesions. For the NOF lesion, fibroxanthoma is the recommended nomenclature since it more closely matches the underlying pathologic features. The size and natural history of FCDs and fibroxanthoma, two nonaggressive fibrous lesions of the bone, have historically set them apart. Both are regarded as nonaggressive and developmental abnormalities. They were originally reported by Lichtenstein and Jaffe in 1942, and they usually appeared around the knee in youngsters during the metaphysis of developing long tubular bones.

Sometimes the non-ossifying fibroma is associated with neurofibromatosis (noncancerous nervous system tumor) or Jaffe-Campanacci syndrome, which is usually found along with mental retardation, hypogonadism, and cafè-au-lait spots (flat, light brown colored birthmark).

What Are the Symptoms of Non-Ossifying Fibroma?

Non-ossifying fibroma is usually asymptomatic. However, sometimes they show the following symptoms:

• Mild soreness or swelling in the affected area of the bone.

• Mild pain at rest as well.

• Decreased strength of the bone sometimes results in a fracture.

What Are the Imaging Techniques Used to Diagnose Non-Ossifying Fibroma and Fibrous Cortical Defects?

The imaging techniques used in the diagnosis of non-ossifying fibroma are:

Plain Radiograph:

1. Non-Ossifying Fibroma:

• In plain radiography, non-ossifying fibroma radiology appears eccentric, round or oval, meta-diaphyseal, and intramedullary radiolucency.

• The margins of the reactive bone appear as a sharp, sclerotic rim with a scalloped contour.

• The medullary rim of the lesion seems thicker than the cortical rim.

• Non-ossifying fibroma starts appearing in the physeal (growth plate of long bone) plate and later appears inside the diaphysis as the normal growth pattern.

• Larger lesions appear multiloculated with dimensions of about four to seven centimeters, and the cortex's endosteal surface is eroded.

• The epiphysis of the bone is never involved.

• Additional imaging techniques are only required once the lesion becomes symptomatic.

2. Fibrous Cortical Defect:

• Focal cortical defects appear as small, round, or oval geographic radiolucencies measuring one to three centimeters.

• The margin of the reactive bone appears sharp and is identified in the areas where the mass impinges the medullary cavity.

• It does not affect the soft tissue and is located inside the distal femoral cortex along their posteromedial aspect and proximal to the adductor tubercle.

• In plain radiography, focal cortical defects are visualized better in the AP (anteroposterior) oblique projection of the femoral bone, with the limb rotated externally to 20 to 40 degrees.

Computed Tomography (CT) Scan:

• In CT scans, fibroxanthoma appears eccentric, intramedullary, sclerotic, well-marginated, and central or cortical lucency.

• In the later stages, reactive sclerosis and heterogeneous lucency are identified.

• The fibrous component of fibroxanthoma has less soft tissue attenuation value, whereas in the later stages, it shows high attenuation.

• CT scans can depict bone involvement and cortical thinning that may result in pathologic fracture.

• If the fibroxanthoma lesion involves more than 50 percent of the width or is found to be more than 33 millimeters, the tubular bone is at higher risk for fracture.

• In case of fracture, the margins are well demarcated, with mild periosteal reaction and mild soft tissue swelling. Soft tissue components are not seen in fibroxanthoma.

Magnetic Resonance Imaging (MRI) Scan:

• Fibroxanthoma appears to have low signal intensity on T1 and T2 weighted spin echo MRIs (magnetic resonance imaging), similar to non-ossified lesions.

• Low signal intensity T2 weighted images represent hemosiderin deposits and increased collagen. Usually, MRI is not taken for focal cortical defects. Due to heterogeneous fibrous areas, the intracortical lesion appears to have a low signal intensity on T1-weighted images and a high signal intensity on T2 and proton density-weighted images.

• The low signal intensity rim represents the sclerotic border. The appearance of fibroxanthoma in T2-weighted images often varies, depending on the healing phase.

Nuclear Imaging:

• A bone scan, also known as skeletal scintigraphy, is a diagnostic tool that uses nuclear medicine in which a special dye called radioactive substances (radiotracers or radiopharmaceuticals) is used to detect bone diseases.

• The lesion's appearance depends on the lesion's phase and is usually negative.

• The radioactive substance technetium-99m has minimal to mild accumulation in fibroxanthoma bone, indicating a benign lesion. The intensity of the uptake is less than that of the active bone lesion. Nevertheless, moderate uptake and mild hyperemia are present, and they refer to the healing phase.

• In children or adults, the eccentric uptake region is located closer to the physis of a tubular bone.

• In children, the findings in nuclear imaging are often masked by a distal femoral epiphyseal plate showing marked tracer uptake.

• The focal cortical defects do not uptake the radioactive substances on bone scans.

Non Ossifying Fibroma vs. fibrous Cortical Defect

• Non-Ossifying Fibroma (NOF): This asymptomatic solitary bone lesion occurs more commonly in children and usually localizes to the metaphysis of long bones. When a kid, for instance, develops it, it normally forms a scab and leaves a scar when it has healed. It looks quite circumscribed, is based on the cortex most often, and possibly provokes cortical formation.

• Fibrous Cortical Defect (FCD): A clinically sovereign, nonmalignant lesion that can be seen in youngsters and is usually less than two centimeter (0.7874 inch) in size. It most commonly occurs in the cortex of the long bones, particularly around the knee joint, and often manifests no symptoms. FCDs are considered normal and are described as a deviation that is self-limited.

What Are the Treatment Options for Non-Ossifying Fibroma?

The treatment options for non-ossifying fibroma include:

• Non-ossifying fibroma usually requires no treatment. It usually resolves on its own once the child completes its growth phase. However, at a later stage, the fracture needs to be stabilized with medical help.

• In rare cases, surgical options such as intralesional curettage and bone grafting may be required.

• Intralesional curettage involves the scraping out of the complete lesion, and a bone graft is performed to replace the missing bone with artificial graft material. This surgery has an excellent recovery rate, and the children can return to regular activities within three to six months.

• A periodic follow-up after the surgery, during which a radiograph is taken to confirm the bone healing and check whether the lesion has recurred, is required.

What Are the Surgical Treatment Options?

During a curettage procedure, the tumor is removed from the bone using specialized instruments. Your surgeon may replace the hole with a bone graft (manufactured in a lab). The bone transplant usually comprises cement, bone from another person, or bone from your kid. In certain cases, your doctors may further attempt to stop the tumor from returning by inserting a chemical into the incision. In cases where the fracture is unstable, or the lesion is particularly extensive, your surgeon is advised to use screws and a plate to support the bone.

What Is the Prognosis?

After surgery, the NOF has a very slim possibility of returning. After children reach adulthood, these lesions can disappear naturally without surgery. Cancer does not develop from them.

Conclusion

Plain radiographs are an effective imaging technique used alone to detect the presence, extent, and location of non-ossifying fibromas. However, as most non-ossifying fibromas are asymptomatic, they are accidentally diagnosed on X-rays taken for other medical conditions. A computed tomography scan effectively shows the extent of the bone involvement and the degree of cortical thinning. Non-ossifying fibroma is more common in boys than in girls, usually between the ages of 10 and 15, and gradually disappears by age 25.