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.

    histopathology

•       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.

Treatment

•       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