Dentistry lectures for MFDS/MJDF/NBDE/ORE: A Note On Clasification Of Fibro-Osseous lesions and Fibrous Dysplasia

Fibro-osseous lesions

• 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,

– Developmental

– Reactive

– Dysplastic

– Neoplastic

CLASSIFICATION

– Fibrous dysplasia

– Cemento-osseous dysplasia

• Focal

• Periapical

• Florid

– Ossifying fibroma

Fibrous dysplasia

• 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

Clinical features

• 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)

Monostotic FD

• Limited to a single bone and can stabilize by puberty.

• 80-85% of cases – jaws more commonly affected - maxilla

• Diagnosed during 2^nd 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

Radiographs

• 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.

Polyostotic FD

• 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.

Clinical features

• 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.