Radiographic Appearance Of Fibrous Dysplasia

Classify fibro-osseous lesions of the jaw. Describe the pathogenesis, clinical features, and radiographic appearance of fibrous dysplasia.
Answer: Fibro-osseous lesions of the jaw: In fibro-osseous lesions, the normal bone is replaced by fibroblasts and collagen fibers with varying amounts of a calcified substance.

World Health Organization Classification (1992)

• Osteogenic neoplasms:
  • Cemento-ossifying fibroma (cement- flying fibroma, ossifying fibroma).
• Non-neoplastic bone lesions:
  • Fibrous dysplasia of jaws
  • Cemento-osseous dysplasia:
    • Periapical cemental dysplasia (peri-apical fibrous dysplasia)
    • Florid cemento-osseous dysplasia
    • Other cemento-osseous dysplasia
• Cherubism
• Central giant cell granuloma
• Aneurysmal bone cyst
• Solitary bone cyst (traumatic, simple, hemorrhagic bone cyst).

Fibrous Dysplasia: Fibrous dysplasia (FD) is a benign intra-medullary genetic disorder of bone that may affect single (monostotic: MFD) or multiple bones (polyostotic: PFD).

Fibrous dysplasia Pathogenesis:

• Fibrous dysplasia is a disorder in the remodeling process of primordial bone to mature bone. Immature, coarse, bony trabeculae are embedded in a dysplastic fibrous tissue matrix with insufficient mineralization.
• There is a gene mutation in the 20q chromosome, and all cell derivatives of the mutant gene manifest dysplastic features.
• McCune-Albright syndrome (MAS) may have a component of fibrous dysplasia. MAS is an intermittent type of syndrome described as a triad of polyostotic, hyper-pigmentation (cafe-au-lait spots), and multiple endocrinopathies like sexual precocity in females.
• Maxillary involvement is more common than mandibular involvement. Craniofacial FD describes FD affecting the maxilla, maxillary sinus, zygoma, sphenoid, temporal, orbital, nasal, frontal, and occipital bones. FD is unilateral and rarely occurs bilaterally.

Fibrous dysplasia Clinical Features:

• Fibrous dysplasia arises within the first or second decades of life. It is slow-growing and causes asymptomatic expansion of the affected bone.
• The degree of deformity depends on the site and extent of bone involvement, (mono or polyostotic type). Facial asymmetry is also present.
• Rapid expansion is rare. There is an acceleration period following the slow growth leading to facial deformity and nerve compression.
• The active growth phase typically slows down during puberty or after skeletal maturation.
• The head is the most common site in monostotic form, and in polyostotic form femur, tibia, and pelvis are involved.
• The prognosis is good, and recurrence following treatment is rare.

Fibrous dysplasia Radiographic Diagnosis:

• The various imaging techniques include:
  • Conventional panoramic technique
  • Computed tomography
  • Magnetic resonance imaging (MRI)
  • Scintigraphy
• The developmental stage and the quantity of bone deposition in the affected site determine the radiographic pattern of the FD. In the conventional tomographic view, well-defined radiolucency represents the early stage of lesion whereas radiodense sclerotic pattern denotes the mature stage of FD.
• The pathognomonic ground-glass or orange peel image pattern reveals the merged boundaries between the fibrous dysplastic bone and the unaffected bone.

Fibrous dysplasia Distinctive Radiographic Features:

• Loss of lamina dura of the teeth in the affected region of the maxilla and mandible.
• Displacement of the inferior alveolar canal in an upward direction.
• Arrangement of abnormal trabeculae in a swirling pattern resembling thumbprint.

Fibrous dysplasia Differential Diagnosis: Nonossifying fibroma, low-grade osteosarcoma, simple bone cyst.

Fibrous dysplasia Management:

• For polyostotic forms, referral to an endocrinologist is mandatory for the diagnosis and management of endocrine abnormalities.
• Bisphosphonates (pamidronate) is used extensively for treating patients with polyostotic disease.
• Surgical resection.