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fibrous dysplasia ( fd ) is a monostotic or polyostotic benign bone lesion with spindle - cell proliferation in woven bone and stroma .
fd are associated with missense mutations in the gnas ( guanine nucleotide - binding protein/-subunit ) gene , which encodes the g - protein -subunit involved in signal transduction via membrane receptors .
histopathological images show characteristically shaped ( c - shaped ) woven bone and , in typical cases , bone formation without osteoblastic rimming on the background of fibrous proliferation containing collagen fibers .
although very rare , cartilaginous differentiation is seen in the lesions of polyostotic fd or fd of the proximal femur .
fd with massive cartilaginous differentiation is also called fibrocartilaginous dysplasia ( fcd ) and is considered a rare variant of fd .
herein , we report on a case of fd of the proximal femur associated with intralesional extensive cartilaginous differentiation in which a pathological fracture occurred during follow - up , with a review of the literature .
an 11-year - old boy with pain in the right hip starting in april 2014 presented to a local hospital .
plain radiography showed an abnormal shadow in the right proximal femur , and he was referred to our department for further examination and treatment .
local findings at the initial examination showed pain upon pressure and tapping tenderness on the outside of the right proximal thigh .
his biochemical blood tests showed no obvious abnormal values except an increase in alkaline phosphatase ( alp ) to 920 iu / l .
plain radiography revealed a bone lesion with a ground - glass appearance associated with a mild increase in the transverse diameter of the bone and thinning of the cortical bone from the metaphysis to the diaphysis of the right proximal femur .
a marked calcification - like shadow associated with a pathological fracture without displacement was seen inside the lesion ( fig .
in addition , multiple areas of bone thickening of the skull with a ground - glass appearance were observed ( fig .
the lesion showed isointensity with punctate low signal intensity in some areas on t1-weighted magnetic resonance imaging ( mri ) images ( fig .
irregular peripheral predominant enhancement was seen on gadolinium ( gd ) contrast - enhanced images ( fig .
bone scintigraphy revealed an accumulation of radioactivity in the right ilium , right proximal femur , right proximal ulna , and skull ( fig .
the above imaging findings led to the diagnosis of pathological fracture associated with a bone tumor in the right proximal femur .
conservative treatment with no weight bearing on the affected limb was performed immediately , and bone union was achieved at the site of the pathological fracture during the course of treatment .
after that , the lesion did not show any trend toward enlargement or other changes on images , and the subjective symptoms such as pain resolved .
, the patient again felt pain in his right hip when he performed a running long jump in a physical education class , and he presented to our emergency room .
plain radiography showed a pathological fracture with displacement in the metaphysis of the right femur ( fig .
, artificial bone was implanted after curettage and fixed with a locking plate so that the varus of the proximal femur was corrected ( fig .
histopathological findings of the specimen obtained by curettage showed that nodular hyaline cartilage tissue was present in the majority of the specimen without marked atypia ( fig .
5a ) . proliferation of fibroblast - like spindle cells and woven bone were evident in part of the lesion ( fig .
two months after surgery , bone union was seen at the site of the pathological fracture , and the patient has had a good clinical course so far .
fcd is a disease that was reported for the first time by pelzmann et al . in 1980 as an fd lesion containing extensive cartilage and considered to be a subtype of fd .
fcd can be said to be very rare , with only 13 cases reported in english so far ( table 1 ) .
histopathological images show extensive cartilaginous tissue in the lesion and , in some cases , chondrocytes with an increased cell density or atypia . therefore , differentiation from bone tumors with similar histological findings , such as enchondroma or chondrosarcoma secondary to fd , is sometimes required .
we conducted a review of the 14 cases of fcd that have been reported so far , including our current case ( table 1 ) . according to these reports [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ]
, there are slightly more males affected , the age of onset ranged widely from 4 to 53 years ( average 18.8 years ) , the proximal femur ( the site of the fcd in our case ) was the most common site , and the ratio of polyostotic to monostotic disease was approximately 1:3 .
the most characteristic feature of fcd on images was calcification in the lesions reflecting cartilaginous tissue .
on the other hand , typical radiographic findings of fd include shadows with a ground - glass appearance and thinning and bulging of the cortical bone , the observation of calcification is not usual . in the present case ,
although pathological findings of fd show irregular immature bone formation without osteoblastic rimming in fibrous tissue , and rarely show very small amounts of cartilage , histological images of fcd are said to show that cartilage with a relatively high cell density is present in the majority and that fd - like findings are seen in parts of it .
therefore , in the diagnosis of fcd , differentiation from multiple enchondromatosis , ollier disease , chondrosarcoma , and chondrosarcoma secondary to fd is necessary , and it seems important to make a careful diagnosis based not only on the pathological findings but also on imaging and clinical findings .
informed consent was obtained from the patient and parents for this case report and any accompanying images .
the authors have no conflict of interest directly relevant to the content of this article .
fibrous dysplasia ( fd ) is a monostotic or polyostotic benign bone lesion with spindle - cell proliferation in woven bone and stroma . 
 rarely , cartilaginous differentiation can be seen in the lesions of fd . 
 fd with massive cartilaginous differentiation is called fibrocartilaginous dysplasia ( fcd ) and is considered a rare variant of fd . 
 although pathological findings of fd show irregular immature bone formation without osteoblastic rimming in fibrous tissue , and rarely show very small amounts of cartilage , histological images of fcd are said to show that cartilage with a relatively high cell density is present in the majority and that fd - like findings are seen in parts of it . 
 the most characteristic feature of fcd on images is calcification in the lesions reflecting cartilaginous tissue . on the other hand , typical radiographic findings of fd 
 include shadows with a ground - glass appearance and thinning and bulging of the cortical bone , the observation if calcification is not usual . 
 therefore , in the diagnosis of fcd , differentiation from multiple enchondromatosis , ollier disease , chondrosarcoma , and chondrosarcoma secondary to fd is necessary , and it seems important to make a careful diagnosis based not only on the pathological findings but also on imaging and clinical findings . 
 herein , we report on a case of fd of the proximal femur associated with intralesional extensive carti laginous differentiation in which a pathological fracture occurred during follow - up , with a review of the literature .