A 4-year-old boy, who was born from a full-term healthy pregnancy, was presented with the complaint of unsteady standing since one-year-old. The symptom was worsened gradually with increasing restricted mobility of the right knee joint and a slowly enlarging mass on the inner side of the right lower thighbone and surrounding soft tissues. Examination found a 3
relatively rigid mass with tenderness at the inner side of right knee. X-rays revealed that the medullary density of the right lower femoral metaphysis was irregularly reduced. CT imaging showed that the density of medullar of metaphysis was irregularly reduced and contained multiple small cysts. The cortex showed irregular thickening, and swelling was found in the proximal soft tissues. However, there was no obvious periosteum reaction (Figure ). A thorough curettage of the lesion was performed. However, seventeen months later, MRI examination revealed a local recurrence in the operated area.
Figure 1 X-ray and CT imaging of the right leg of the case. A. X-ray showed that the pattern of bone was generally normal and there was no swelling of surrounding soft tissue. Density of the metaphysis of the lower right thighbone had irregularly reduced. B and (more ...)
Microscopically, the tumor occupied the medulla and eroded parts of the cortex, but the remaining bone trabeculae still displayed prominent osteoblastic rimming. The first characteristic noted in the case was the distinctive nodular histological feature, which was composed of oval-to-spindle cells and formed abundant vascular networks. The oval-to-spindle cells had congregated and circled to form a central vessel-like structure, which was filled with red blood cells. These oval-to-spindle cells were considered likely to be the key of GCAB pathogenesis and had the ability to form a functional blood vessel within the tumor. The vascular endothelial cell markers-positive further confirmed that the oval-to-spindle tumor cells have the characteristics of vascular endothelial cells and pericytes. The second characteristic of GCAB was the abundance of mononuclear and multinucleate giant cells sprinkled throughout the tumor. The multinucleate giant cells and large mononucleate cells exhibited a distinctively strong expression pattern of CD68, which indicated a general histocytic lineage. The third characteristic of GCAB was the sparse presence of spindle- and spider-shaped cells, and mast cells, scattered throughout the loose mesenchyme of the tumor and accompanied by significant edema, myxoid or fibrosis in interstitial compartment. However, as this case was older than our former case (4-years vs. 15-months) and the history of tumor-associated symptoms was longer, this characteristic was not obvious. Therefore, it might suggest that the oval-to-spindle cells have a tendency to proliferate and replace the regions of loosened mesenchyme or collagen over the pathogenic course of GCAB. In addition, widespread deposition of hemosiderins was observed and might be included as the fourth characteristic of GCAB (Figure ).
Figure 2 Microscopic features of the case.A. The tumor formed by dense and loose cell regions. The dense regions were composed of plexiform and nodular oval- to spindle-shaped tumor cells. The loose regions were composed of fibrosis. Bone trabeculae erosion was (more ...)
Immunohistochemical staining showed that most of the oval-to-spindle cells, large mononuclear cells, multinucleate giant cells, and periendothelial cells were strongly positive for vimentin, but uniformly negative for calponin, h-caldesmon, AE1/AE3, desmin, and CD1a. The perivascular cells of the vessels strongly expressed calponin and h-caldesmon. The monolayered small channels and oval-to-spindle cells in nodular or linear aggregate areas were positive for expression of vascular endothelial cell markers, CD31 and CD34, and partly expression of FVIII. SMA was most robustly expressed in the perivascular cells of the well-developed vessels and monolayered small channel in the hemangioma-like areas. Other regions of the tumor showed weak or no staining for SMA. The large mononuclear cells and multinucleate giant cells exhibited strong expression of the classic macrophage marker, CD68, but negative for Desmin, S-100, LCA, and SMA (Figure ).
Figure 3 Immunohistochemical staining of GCAB.A. Vimentin-positivity throughout the tumor. B. SMA-positivity in perivascular cells of the well-developed vessels and basement membrane. C. CD68-positivity was strong in the giant cells, weak in some oval-to-spindle (more ...)