Oral and Maxillofacial Pathology II: Bone Diseases

Classification of Bone Diseases

• Bone diseases can be classified into 7 categories: Developmental, Metabolic, Inflammatory, Cystic, Tumors, Hormonal, and Deficiency

Developmental Bone Diseases

• Fibrous Dysplasia: a developmental tumorlike condition characterized by replacement of normal bone by fibrous connective tissue with irregular bony trabeculae (fibro-osseous lesion)

Fibrous Dysplasia

• Can occur in three forms: Monostotic, Polyostotic, and Syndrome-related
• Monostotic FD: affecting a single bone
• Polyostotic FD: affecting multiple bones
• Syndrome-related: associated with McCune-Albright Syndrome or Jaffe Type

McCune-Albright Syndrome

• Results from mutation of a pluripotent stem cell in the early stages of embryonic development
• Characterized by multiple bone lesions (polyostotic), cutaneous (café au lait) pigmentation, and endocrine disturbances

Jaffe Type

• Results from mutation of osteoblasts and melanocytes
• Characterized by multiple bone lesions (polyostotic) and cutaneous (café au lait) pigmentation

Facial Fibrous Dysplasia

• Monostotic fibrous dysplasia affecting the maxilla
• Etiopathogenesis: Non-heritable post zygotic somatic mutation in GNAS1 gene
• Clinical features: painless, unilateral, slowly growing swelling, proptosis, maxillary sinus obliteration, nasal obstruction, and dental manifestations

Radiographic Features of Facial Fibrous Dysplasia

• 3 patterns depending on the amount of formed lesional bone: Orange peel pattern, Ground-glass appearance, Ill-defined radiolucent pattern with few faint trabeculae of bone, and Smoke screen pattern

Microscopic Features of Facial Fibrous Dysplasia

• Osteoid stage: Resorption of the original bone and replacement by dysplastic fibrous tissue, Trabeculae of osteoid/woven bone are laid down equidistant from each other and are Chinese letter shaped or U,C and W shaped
• Osseous stage: Calcification of osteoid occurs & formation of woven bone is complete without osteoblastic rimming, Resorption of the new trabeculae occurs and the whole cycle is repeated

Complications of Facial Fibrous Dysplasia

• Malocclusion, Rarely osteosarcoma, Deformity of the orbit, Obliteration of the maxillary sinus

Treatment of Facial Fibrous Dysplasia

• Plastic surgery after 21 years of age

Cherubism

• Developmental jaw swelling, its growth stops with cessation of the skeletal growth
• Etiopathogenesis: Hereditary, AD, Cherubism gene (SH3BP2) which enhances osteoclastogenesis