Sunday, August 7, 2011

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 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


























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

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