fibrous dysplasia is not hereditary in nature and it caused by mutation in the gnas1 ( guanine nucleotide binding protein , alpha stimulating activity polypeptide ) gene ( 20q13.2 ) and this gene encodes a g - protein which results in overproduction of camp in the affected tissues .
furthermore , there is increased the proliferation of melanocytes thus results in cafe - au - lait spots .
fibrous dysplasia has three clinical patterns namely monostotic , polyostotic , craniofacial form . about 3% of lesions associated are with skin pigmentation and hyperfunctioning endocrine disorders known as the mccune  albright syndrome .
the skull base and proximal metaphysic of femora are two sites most commonly involved . in the skull fd
involves skull bases and facial bones . in childhood fd presents as facial asymmetry or a bump , but symmetric expansion of malar prominences and/or frontal bosses may be seen .
due to abnormal growth and deformity of craniofacial bones may result in encroachment on cranial nerves .
female patients experience increased pain level during pregnancy and during the menstrual cycle because of estrogen receptors found in fd .
bianco et al . demonstrated that fd is a disease of bone marrow stromal cells ( bmsc ) .
the bmscs form structural framework upon which hematopoiesis occurs in the bone marrow and a subset of bmsc are multipotent stem cells capable of differentiating into multiple cells including osteoblasts , osteocytes , chondrocytes , bone marrow adipocytes and other cells . in fd bmsc differentiate along osteogenic lineage , but differentiation is arrested and instead undergo proliferation giving rise to fibro - osseous masses of tissue .
g - protein is central in cell originating pathway leads to the generation of intracellular second messenger , camp / protein kinase a signaling .
all mutation in gs alpha identified in association with fd is the 201 position . in >
95% cases arginine is replaced by either cysteine or histidine ( r201c or r201h ) .
this result in inhibition of intrinsic gtpase activity of gs alpha protein and it is this aspect that leads to constitutive , ligand - independent generation of intercellular camp .
gene amplification techniques such as polymerase chain reaction is now possible to test for genetic mutation in peripheral blood samples .
actively formed lesions in adolescents have greatly increased isotope update that corresponds closely to radiographic extent of the lesion .
some characteristic feature is bar - shaped pattern , whole - bone involvement and close match between the size of the lesion on radiograph and the size of the area of uptake .
the extent of the lesion is visible clearly on computed tomography , and cortical boundary is depicted more clearly than radiograph .
the thickness of cortex , endosteal scalloping and periosteal new bone reaction and homogeneity of the poorly mineralized lesional tissue are well demonstrated .
delicate trabeculae of immature bone with no osteoblastic rimming enmeshed within a bland fibrous stroma of dysplastic spindle - shaped cells without any cellular features of malignancy .
variable number of immature , nonstress oriented , disconnected dysplastic trabeculae floating in a sea of immature mesenchymal cells that have little or no collagen about them .
change is noticed . the malignant transformation rate is unknown , but it is likely to be not > 1% .
cancer is more likely to occur in polyostotic disease , and most common histological types were osteosarcoma , fibrosarcoma and chondrosarcoma .
there are also reports suggesting that the malignant transformation may be more common in mazabraud 's syndrome ( fd in association with intramuscular myxomas ) .
the findings in various studies showed that high dose intravenous pamidronate decreases pain and the markers of bone metabolism .
 fibrous dysplasia ( fd ) is a benign intramedullary fibro - osseous lesion . 
 fd is a bone developmental anomaly characterized by replacement of normal bone and marrow bone by fibrous tissue . 
 it involves any of the bones as single lesion ( monostotic ) or in multiple bone lesions ( polyostotic ) or all of the skeletal system ( panostotic ) . 
 long bones are most commonly involved , which mostly identified incidentally and clinically appears asymptomatic . 
 clinical , radiographical and histopathological findings will help in confirming the lesion . 
 there are many treatment option available , but still management of fd remains challenging . 
Etiology
Clinical Features
Pathophysiology
Diagnosis
Malignant Transformation
Treatment