fd may occur in one bone ( monostotic ) or multiple bones ( polyostotic ) and may be associated with other conditions like mccune albright syndrome .
clinical presentation may occur at any age , with the majority of lesions being detected by the age of 30 years .
common sites of skeletal involvement are the long bones , ribs , craniofacial bones , and the pelvis .
a 32-year - old female presented with pathological fracture of the shaft of the right femur . radiological evaluation revealed features of fd ( with fracture of the right femoral shaft ) , with similar lesions in the opposite femur .
the right femoral fracture was treated with intramedullary nailing , and intraoperative biopsy confirmed the diagnosis of fd . in order to document the extent of bony involvement in the rest of the skeleton , whole body bone scintigraphy was performed 3 hours after intravenous injection of 99mtc - methylene diphosphonate ( mdp ) .
multiple sites of increased skeletal tracer uptake were detected in the skull , left mandible , multiple ribs , pelvis and both lower limbs [ figure 1 ] .
single - photon emission computed tomography / computerized tomography ( spect / ct ) of the skull was performed for evaluation of the extent of skull bone involvement and showed involvement of the right sphenoid , ethmoid and frontal bones and left mandible , with evidence of bone expansion [ figure 2 ] .
ct component of spect - ct [ figure 3 ] shows bony expansion with ground glass appearance involving right sided ribs .
involvement of the sphenoid wing ( commonly described as the  pirate sign  ) was also better depicted with spect / ct .
tc-99 m mdp whole body images show multiple sites of increased tracer uptake , including the skull and facial bones , multiple ribs , pelvis and bones of both lower limbs .
the  pirate sign  indicates involvement of the right sphenoid wing hybrid spect / ct fusion to determine the extent of skull and facial bone involvement shows intense tracer uptake in the sphenoid , ethmoid and frontal bones non - contrast ct scan of the chest shows bony expansion and deformity of the right ribs , where intense osteoblastic activity was detected
fd is postulated to occur as a result of a developmental failure in the remodeling of primitive bone to mature lamellar bone and a failure of the bone to realign in response to mechanical stress .
failure of maturation leaves a mass of immature isolated trabeculae enmeshed in dysplastic fibrous tissue that constantly turns over but never ( or very , very slowly ) completes the remodeling process . the combination of a lack of stress alignment and insufficient mineralization results in substantial loss of mechanical strength , leading to the development of pain , deformity , and pathologic fractures .
the etiology has been linked with a mutation in the gs alpha gene that occurs after fertilization in somatic cells and is located at chromosome 20q13.2 - 13.3 .
the monostotic presentation of fd is more frequent than polyostotic presentation , and lesions enlarge in proportion to skeletal growth .
polyostotic lesions often continue to enlarge after skeletal maturity , with progressive deformity and an increase in pathologic fractures .
patients with polyostotic disease and large , painful lesions in weight - bearing long bones are at the greatest risk for pathologic fracture
. local expansion of fd in the maxilla , zygomatic , or ethmoid bones of the face can produce substantial functional and cosmetic deformity . at the initial presentation ,
radionuclide bone scintigraphy is useful to demonstrate the extent of the disease . actively forming lesions in adolescents
have greatly increased isotope uptake that corresponds closely to the radiographic extent of the lesion .
polyostotic fd has been demonstrated using f18-fluoride positron emission tomography / computed tomography ( pet / ct ) .
the utility of volume rendering has also been demonstrated in evaluation of the bony deformities .
the  pirate sign  has been previously described on planar bone scintigraphy in fd .
recent studies have described the advantage of performing bone spect in addition to ct to determine the extent of fd in the skull base and of hybrid spect / ct imaging in fd of the lumbar vertebra .
the present case illustrates the utility of hybrid spect / ct in documenting the complete extent of bony involvement of the skull base .
 polyostotic fibrous dysplasia is a rare progressive benign disorder of the bone . 
 bone scintigraphy is extremely useful in the initial evaluation for identifying the extent of disease . 
 we report a case presenting with pathological fracture of the shaft of the right femur . 
 after treatment of the fracture , bone scintigraphy revealed involvement of multiple bones including the skull and facial bones . 
 the utility of single - photon emission computed tomography / computerized tomography in the evaluation of the extent of skull base involvement is highlighted . 
INTRODUCTION
CASE REPORT
DISCUSSION