PMC9262566_01
Case 3, a 55-year-old female with a pathological fracture of the femur with underlying GCTB. (a) X-ray at the time of diagnosis showed a pathological fracture through a well-defined osteolytic lesion with a sclerotic margin in the distal femur meta- and epiphysis, initially treated by external fixation. (b) Coronal and (c) sagittal CT images at the time of diagnosis showed the pathological fracture extending through the anterior and posterior cortices (arrows) and no internal matrix. (d) Morphology at the time of curettage shows many mononuclear stromal cells intermixed with large osteoclast-like giant cells without atypical morphological features. (e) At the time of curettage; areas with reactive woven bone with typical osteoblast lining are seen, which may be due to the clinical fracture. (f) At the time of curettage; heterogeneous positive H3G34W staining in stromal cells.
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An X-ray at the time of initial presentation showed an osteolytic lesion in the distal femur meta-epiphysis complicated by an intra-articular pathological fracture, for which external fixation was performed (Figure 2(a)). Cortical scalloping was present on CT and no matrix formation was noted (Figures 2(b) and 2(c)). Biopsy confirmed the diagnosis of conventional GCTB (Figures 2(d)-2(f)).
Case 3, same case as in Figure 2; local recurrence occurred 1 year after curettage, followed by denosumab treatment. After en bloc resection, the diagnosis of malignant GCTB was made. (a) Coronal CT image performed for follow-up approximately 1 year after surgery showed osteolysis along the medial bone-cement interface (arrows) in keeping with local recurrence. Denosumab treatment was started after this scan. (b) Coronal CT image after 10 months of denosumab therapy showed increased density in the osteolytic area of recurrence due to formation of fibro-osseous tissue (vertical arrow at the medial femoral condyle), the tumor expanded further into the soft tissues with an irregular margin (horizontal arrows). In addition, proximal to the area of local recurrence there was a newly formed component of osteoid matrix (dotted arrows), suspicious for progression to osteosarcoma. (c) Photograph of tumor macroscopy (sagittal section) after en bloc resection shows the cementum from the previous surgery, surrounded by tumor tissue extending into the soft tissue. (d) Sagittal CT reformatted after the macroscopy section (Figure 3(c)) shows endomedullary cement and holes due to previous screw tracts, surrounded by denosumab changes (asterisk). Posterior soft tissue mass is noted with osteoid matrix formation suspicious for an osteosarcoma (dotted arrows). (e) Histology at the time of resection; low power view displaying highly cellular spindle cell proliferation with areas of tumor necrosis (left) and the formation of tumor osteoid (right). Scale bar of 50 mum. (f) Tumor osteoid in high-power field fitting with the histological features of an osteosarcoma. Scale bar 50 mum.
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On a follow-up CT of the knee performed 1 year later, new osteolysis was present medial of the cement with cortex destruction, interpreted as a local recurrence (Figure 3(a)). However, within the increased soft tissue mass there was new osteoid matrix formation proximally, suspicious of malignant transformation in GCTB (Figure 3(b)). En bloc resection was performed, the macroscopic resection specimen (Figure 3(c)) and preoperative sagittal CT reformatted image (Figure 3(d)) showed corresponding endomedullary fibro-osseous matrix formation (asterisk) with osteoid deposition in a posteromedial new mass lesion. Histological features were in keeping with a high-grade osteosarcoma (Figures 3(e) and 3(f)).