PMC6106748_01
Conventional AP and lateral radiographs (top left and top middle) show an expansive bubbly lytic bone lesion in the diaphysis-metaphysis of the right distal radius with a narrow zone of transition, nonsclerotic margins, cortical thinning and destruction, and an accompanying large soft-tissue mass which appears to compress the distal ulna with bowing of the latter. Bone scintigraphy (top right) shows no increased uptake at the location of the lesion. MRI with coronal T1-weighted (bottom left) and gadolinium-enhanced T1-weighted (bottom middle) images, and axial T2-weighted and gadolinium-enhanced fat-suppressed T1-weighted images (bottom right) are in keeping with the conventional radiographic findings, and also demonstrate no signs of invasion in surrounding muscles or ulna. Remarkably, in the center of the lesion there is low signal on all sequences (arrows), most strikingly on the T2-weighted sequence. Because the combined imaging features suggest a slow-growing (most likely benign) process with fibrotic components, the differential diagnostic considerations include desmoplastic fibroma, and (less likely) giant-cell tumor or fibrous dysplasia
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Fig1
As shown in Fig. 1, X-ray examination revealed a large lobulated, compartmentalized, osteolytic, expansive tumor mass in the metadiaphysis of the distal radius.
Histology, karyotype and beta-catenin nuclear expression in DF. a Histology showing a fibroblastic tumor with little or no nuclear atypia or mitotic activity (H&E, original magnification x 200). As such, the histology of DF resembles that DF-LGCOS shown in Fig. 4a. b DF karyotype: 47,XX,+8[2]/46,XX[18]. c IHC expression of beta-catenin in several tumor cell nuclei of DF (original magnification x 400)
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Fig2
Mitoses were not found (Fig. 2a). 
Conventional AP, lateral radiographs and gross morphology of DF-LGCOS. a Conventional AP, lateral radiographs (top left and top middle) show an expansive osteolytic lesion in the diaphysis-metaphysis of the right distal femur with an ill-defined border and cortical destruction. Bone scintigraphy (top right) demonstrates increased uptake at the location of the lesion, but no suspicious uptake elsewhere. MRI with sagittal T1-weighted (bottom left) and fat-suppressed proton density-weighted (bottom middle) images, and axial T1-weighted and gadolinium-enhanced fat-suppressed T1-weighted images (bottom right) show the T1 hypointense, T2 hyperintense, and vividly enhancing lesion in the right distal femur as a large soft-tissue mass with cortical breakthrough and extra-osseous expansion. The combined imaging features are highly suggestive of an aggressive malignant lesion, with osteosarcoma, Ewing sarcoma, and chondrosarcoma being the main differential diagnostic considerations. b Gross specimen of DF-LGCOS, showing a white, fibrous tumor of the distal femur with cortical breakthrough and invasion of soft tissue. As such, the gross appearance of DF-LGCOS resembles DF
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Fig3
There was strong tumor enhancement after administration of intravenous gadolinium (Fig. 3a). There was extension to surrounding soft tissue (Fig. 3b). 
Histology, karyotype and CDK4 expression in DF-LGOS. a Histology showing a fibroblastic tumor with permeative invasive growth (H&E, original magnification x 100). As such, the histology of DF-LGCOS resembles that of DF, shown in Fig. 2a. b DF-LGOS karyotype: 47~49,XX,del(13)(q12q32),+1~2r,+1~2mar,1dmin[cp17]/46,XX[2]. c Diffuse nuclear expression of CDK4 in cell nuclei of DF-LGCOS (original magnification x 200)
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Fig4
As shown in Fig. 4a, this tumor also consisted of bundles of moderate cellular tissue, with fibroblast-like, spindle cells in abundant collagenous stroma. As depicted in Fig. 4b, cytogenetic analysis showed an abnormal karyotype: 47~49,XX,del(13) (q12q32),+ 1~2r,+1~2mar,1dmin [cp17]/46,XX [2]. With IHC, tumor cells exhibited strong nuclear staining for CDK4 (Fig. 4c) and moderate nuclear staining for SATB2.