permission was obtained from the patient included in this report . in june 2014 , a 25-year - old woman presented to the outpatient clinic with a 6-month history of progressive left hip pain .
physical examination revealed mild pain with motion in the hip joint and slightly limited range of motion .
radiographs showed a large osteolytic lesion with well - defined margins in the proximal metaphysis of the femur , partially surrounded by sclerotic cortical bone ( fig .
1 ) . magnetic resonance imaging ( mri ) showed a well - demarcated intra - osseous lesion measuring 584242 mm .
t1-weighted images demonstrated a lesion with heterogeneously distributed low- and high - signal intensities , while t2-weighted images revealed similar findings , partially surrounded by areas of low signal intensity , concordant with reactive bone sclerosis .
fat - suppressed images showed an area of low signal intensity at the center of the lesion .
a radionuclide bone scan demonstrated a lesion with peripherally increased uptake of tc-99 m methyl diphosphonate ( mdp ) in the metaphysis of the femur in the area of radiographic abnormality ( fig .
these findings reflected benign bone tumor , such as intraosseous lipoma or liposclerosing myxofibrous tumor , rather than fibrous dysplasia , giant cell tumor , aneurysmal bone cyst , or simple bone cyst .
because the lesion was suspected to be a benign bone tumor with progressive pain leading to impending fracture , surgery was performed in august 2014 .
curettage of the lesion and bone grafting were performed with a femoral head allograft , which was stored in our bone bank .
prophylactic internal fixation using the zimmer natural nail system ( zimmer , warsaw , in , usa ) was performed to prevent pathologic fracture ( fig .
macroscopically , the pathologic specimen had abundant tan - brown soft tissue and multiple bone fragments .
these histiocytes showed abundant foamy cytoplasm , and were positive for cd68 but negative for cd1a and s100 ( fig .
after surgery , we evaluated the lipidemic status of the patient including her family history .
she had no relevant history of elevated laboratory results , but her mother did have a history of hyperlipidemia .
laboratory tests revealed the following results : fasting blood glucose , 95 g / dl ; hba1c , 5.4% ; total cholesterol , 157 mg / dl ; triglycerides , 63 mg / dl ; high - density lipoprotein cholesterol , 44 mg / dl ; and low - density lipoprotein cholesterol , 101 mg / dl .
immunoelectrophoretic fractionation of lipoprotein revealed normal values for alpha , pre - beta , beta , and chylomicrons .
implant removal and bone grafting with allograft bone chip for new bone formation were performed to remove foreign body sensation .
there was no sign of local recurrence and the patient could successfully perform normal activities at the last follow - up ( fig .
pix is an extremely rare , benign bone tumor that usually occurs in the appendicular skeleton , such as the calcaneus , rather than the axial skeleton .
the lesion in this patient showed a sharply defined lytic lesion with a narrow zone of transition , and partially or completely sclerotic margins .
these characteristics also are seen in intraosseous lipoma , liposclerosing myxofibrous tumor , simple bone cyst , aneurysmal bone cyst , non - ossifying fibroma , chondroblastoma , giant cell tumor , and fibrous dysplasia . the location of the lesion made it difficult to include pix in the differential diagnosis preoperatively .
pix can exhibit an aggressive appearance , with an expansile border or cortical disruption , and may mimic malignancy , such as multiple myeloma or metastatic bone tumor3 ) .
mri is typically characterized by a circumscribed area of heterogeneous signal intensity on t1- and t2-weighted images , and associated loss of signal when fat is suppressed , which is hypothesized to result from the cholesterol - laden histiocytes seen on histopathology5 ) .
the typical histopathologic appearance of pix is a lesion consisting of numerous foamy cells and non - foamy mononuclear or multinucleated giant cells , and , occasionally , touton - type giant cells6 )
. abundant cholesterol clefts with giant cells at the focal area and cholesterol clefts between bone spicules also can be seen in the lesion7 ) . in our case
, we could see numerous foamy cells and multinucleated giant cells , but touton - type giant cells and cholesterol clefts between bone spicules were not observed .
giant cell tumor and intra - osseous lipoma might be considered in the differential diagnosis .
giant cell tumors usually show a lytic lesion in the epiphysis , rather than in the metaphysis , and sometimes grow to the articular surface .
the key histopathologic appearance is multinucleated giant cells with up to 100 nuclei that have prominent nucleoli8 ) .
intraosseous lipomas are usually located in the long bones and have radiologic findings similar to pix .
however , a well - defined lesion with sclerotic borders and mineralization of the central lesion are often pathognomonic . computed tomography and mri also can be diagnostic because they show high composition of fat content in the lesion9 ) .
however , we suggest that this lesion is highly associated with familial factors because her mother had a history of hyperlipidemia .
further study is needed to investigate the specific genes associated with xanthoma in patients with a family history of hyperlipidemia .
when pix is accompanied by progressive pain or aggressive appearance , the optimal treatment typically consists of curettage of the lesion and bone grafting10 ) .
the necessity of prophylactic internal fixation depends on the location and extent of the lesion .
because the pelvis , proximal femur , and tibia are particularly prone to pathologic fracture , internal fixation may be indicated . in this patient , although the lesion did not exhibit an aggressive appearance , it showed extensive osteolysis with thin cortical bone accompanied by progressive pain in the left proximal femur .
thus , internal fixation was performed to prevent pathologic fracture . in conclusion , we report a rare case of pix of the proximal femur in a patient without hyperlipidemia
. this diagnosis can be difficult to make preoperatively using clinical examination , laboratory findings , and imaging studies .
the variable clinical and radiologic characteristics of pix reinforce the necessity of bone biopsy to confirm diagnosis .
 we report the case of a 25-year - old woman presenting with left hip pain . a lesion was found in the proximal femoral metaphysis . benign bone tumor , such as intraosseous lipoma or liposclerosing myxofibrous tumor , 
 was suspected based on simple radiographs and magnetic resonance images . 
 curettage of the lesion and bone grafting was performed . 
 histologic findings reflected primary intraosseous xanthoma of the proximal femur . 
 laboratory tests revealed the patient to be normolipidemic , while immunoelectrophoretic fractionation of lipoproteins revealed normal values for alpha , pre - beta , beta , and chylomicrons . at the one - year follow - up 
 , there was no evidence of local recurrence . 
 this is the first reported case of primary intraosseous xanthoma of the proximal femur in a normolipidemic patient . 
CASE REPORT
DISCUSSION