Fibrous dysplasia of bone

MRI semiotics of fibrous dysplasia

Magnetic resonance imaging is the primary method for evaluating the structure of pathological lesions. In the polyostotic form of dysplasia, multiple (multifocal) lesions are frequently detected in the femora (femora) and lower leg bones.

• T1-weighted images (spin echo, coronal plane): The baseline signal intensity generally ranges from low to intermediate. However, when hemorrhage occurs within the lesion structure (e.g., in the femoral neck), a combined signal with areas of marked hyperintensity is formed.
• T2-weighted images (fast spin echo, sagittal and axial planes): Intensity directly depends on tissue morphology. The predominantly fibrous component yields an intermediate signal, whereas areas undergoing cystic changes or containing a hemorrhagic component appear hyperintense. Using a fat-suppression mode allows for better differentiation of these components.
• Specific findings: Internal partitions (septa) and characteristic fluid-fluid levels may be visualized within the lesions. Following intravenous contrast administration, uniform or septal enhancement is noted.

If chondroid calcification is detected within the structure, this directly indicates fibrocartilaginous dysplasia (fibrocartilaginous dysplasia). Malignant transformation in this pathology is extremely rare, typically occurring against the background of prior radiation therapy.

Osteofibrous dysplasia (OFD): clinical profile

Osteofibrous dysplasia is a rare form of lesion with specific age and anatomical characteristics. Histologically, it resembles classical fibrous dysplasia and adamantinoma stroma (adamantinoma).

The disease debuts between birth and 40 years of age, with approximately 50% of all diagnosed cases occurring in children under 10 years old. The male-to-female ratio is completely equal.

In the vast majority of cases (over 90%), the tibia (tibia) is affected. Typical localization is the anterior cortex of the middle third of the diaphysis. The process can be multiple within a single bone. In one out of five patients (20%), the ipsilateral fibula (fibula) is additionally involved, and bilateral limb involvement has also been described in practice.

Visualization and differential diagnosis of OFD

Radiological features of osteofibrous dysplasia evolve as the patient grows:

1. In early childhood: The pathological lesion actively expands and deforms (bows) the tibia, forming a dense sclerotic rim at the periphery.
2. In patients older than 3 months: The lesion acquires an eccentric, multilocular appearance. The matrix structure may be entirely lytic or feature ground-glass mineralization, making it visually indistinguishable from classical fibrous dysplasia.

Cross-sectional imaging methods (MRI and CT) are essential to confirm the intracortical origin of the lesion. On MRI (including axial proton density-weighted images with fat suppression), the lesions appear lobulated, surrounded by a low-intensity rim. On T1-weighted images, the signal is intermediate; on STIR, it is persistently high; and on T2-weighted images, it is variable, depending on the degree of cystic degeneration.

An important prognostic sign is invasion into the medullary canal. It is quite common, but complete canal involvement (observed in 30% of cases) is a red flag—in such situations, OFD-like adamantinoma must be ruled out. The contrast enhancement pattern ranges from diffuse to heterogeneous or peripheral.

Class and exam questions

What else to study on this topic

• Mechanisms of fluid-fluid level formation in bone neoplasms.
• Differential diagnosis of ground-glass mineralization.
• Histological relationship between osteofibrous dysplasia and adamantinoma.
• Features of the radiological pattern in the polyostotic form of dysplasia.
• Specifics of using fat-suppression MRI sequences in bone imaging.

Other topics in the "Musculoskeletal System" section

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