• Diverse group of processes characterized by replacement of normal bone by fibrous tissue containing newly formed mineralized product. (Not a specific diagnosis)
• Includes lesions of,
– Fibrous dysplasia
– Cemento-osseous dysplasia
– Ossifying fibroma
• Defined as a non-neoplastic, primary disorder of bone in which normal medullary bone is replaced by a variable amount of structurally weak fibrous and osseous tissue.
• A developmental tumor like condition that is characterized by replacement of normal bone by an excessive proliferation of cellular fibrous connective tissue intermixed with irregular bony trabeculae.
• Mutation involving GNAS1 gene
• FD can manifest as,
– Involve only one bone (Monostotic) – mutation in post natal life (confined to one site)
– Involve multiple bones (Polyostotic) – mutation of skeletal progenitor cells and their progeny will involve development of multiple bones.
– Multiple bone lesions in conjunction with cutaneous and endocrine abnormalities – mutation of undifferentiated stem cells in early embryonic life (osteoblasts, melanocytes and endocrine cells)
• Limited to a single bone and can stabilize by puberty.
• 80-85% of cases – jaws more commonly affected - maxilla
• Diagnosed during 2nd decade
• Males and females are equally affected
• Painless, slow growing swelling of affected area
• Teeth are displaced but remain firm.
• Mandibular – truly monostotic
• Maxilla – can involve adjacent bones – zygoma, occipital, sphenoid – Craniofacial FD
• Ground glass opacification – poorly calcified bone trabeculae arranged in a disorganized pattern.
• Margins blend into the normal bone
• Expansion of buccal, lingual plates with bulging of lower border
• Superior displacement of inferior alveolar canal
• Obliteration of maxillary sinus
• Increased density in base of skull – occiput, sphenoid, roof of orbit and frontal bones – FD of skull.
• Involvement of 2 or more bones and continues to grow.
• Jaffe-lichtenstein syndrome – polyostotic FD with café au lait (Coffee with milk) pigmentation.
• Mccune-Albright syndrome - polyostotic FD with café au lait pigmentation and multiple endocrinopathies – sexual precocity in females, pituitary adenoma or hyperthyroidism.
• Facial asymmetry
• Symptoms are related to long bone lesions like pathologic #
• Involvement of upper portion of femur leads to leg length discrpancy – Hockey stick deformity
• Café au lait pigmentation – well defined, unilateral, tan macules on trunk and thighs. The margins are irregular whereas in NF, the margins are smooth.
• Irregularly shaped trabeculae of immature (woven) bone in a cellular, loosely arranged fibrous stroma.
• Trabeculae are not connected with each other, assume curvilinear shapes – Chinese script writing
• Arise by metaplasia and are not surrounded by osteoblasts.
• Monotonous pattern throughout the lesion.
• Fuses directly with the normal bone without any line of demarcation.
• Can undergo progressive maturation.
• Surgical resection
• Disease tends to stabilize and stops enlarging when skeletal maturation is reached.
• Regrowth of the lesion in 25-50% of cases – more in younger pts