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E1458. The Giant in the Room! Osteoclastomas/Giant Cell Tumor of the Bone
Authors
  1. Asem Rahman; Virginia Commonwealth University Medical Center
  2. Josephina Vossen; Virginia Commonwealth University Medical Center
  3. Peter Haar; Virginia Commonwealth University Medical Center
  4. Mauricio Jimenez; Virginia Commonwealth University Medical Center
Background
Giant cell tumor of bone (GCT) is a benign, locally aggressive bone tumor characterized histologically by multinucleated giant cells with a background of mononuclear stromal cells. Majority of GCT appear as lytic lesion in the metaphyseal/epiphyseal location with well-defined but nonsclerotic margin, eccentric in location, extending to the subchondral bone in a patient with closed physes.

Educational Goals / Teaching Points
1. Review the clinical findings and patient population affected by GCT. 2. Familiarize the reader with the different radiological appearances of aggressive vs non aggressive GCTs. 3. Review clue imaging findings for evaluation of recurrent vs residual disease on Radiograph, CT and MRI. 4. Discuss the differential diagnosis and imaging findings valuable in the differentiation between these lesions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Giant cell tumor of bone (GCT) is a benign, locally aggressive bone tumor characterized histologically by multinucleated giant cells with a background of mononuclear stromal cells. The typical radiological appearance of GCT is a lytic metaphyseal lesion with epiphyseal extension with well-defined but nonsclerotic margin, in location, extending to the subchondral bone in a patient with closed physes. MR imaging findings are nonspecific, presenting with intermediate or low T1 signal intensity on T1-weighted images, intermediate to increased T2 signal intensity on T2 weighted images and diffuse to heterogeneous enhancement after contrast administration. Technetium 99m–MDP shows increased radiotracer uptake along the periphery of the lesion with central photopenia due to osteolysis or necrosis. Aggressive features include a wide zone of transition, cortical thinning/fracture, expansile remodeling, and bone destruction with soft-tissue mass. Secondary aneurysmal bone cysts (ABC) can be seen inside the GCT with fluid fluid levels in approximately 14% of cases. GCT may also occur in flat bones or an apophysis which usually demonstrate a less classic appearance. Giant cell tumors in the greater trochanter of the femur have only rarely been reported. Up to 15% of cases may involve flat bones such as the pelvis, sacrum, spine, ribs, and calvaria. GCT may exhibit metastasis or undergo malignant transformation. Usually the transformation is into a high-grade sarcoma which has a poor prognosis. Surgery is the main treatment with advocates of varying surgical techniques ranging from intra-lesional curettage to wide resection. Denosumab, a monoclonal antibody that targets the osteoclastic activity of GCT, has produced 90% tumor necrosis in early studies, results indicative of promise as a potential adjuvant therapy.

Conclusion
Giant cell tumor of bone (GCT) is a benign, locally aggressive bone tumor of young adult and adults. Characterized radiologically as lytic lesion in the metaphyseal/epiphyseal location with well-defined but nonsclerotic margin, eccentric in location, extending to the subchondral bone in a patient with closed physes. Adequate radiologic identification, characterization of the lesion and knowledge of differential diagnosis will have an impact on patient outcome and treatment.