DISCUSSION
Because of the lesion's location, the patient's age, and the radiographic and MRI findings, the diagnosis was thought to be either a giant cell tumor (GCT) or a telangiectatic osteosarcoma. The specialist who was consulted for further workup ordered a biopsy. The pathology report confirmed that the lesion was a GCT.
GCTs are rare, comprising 4% to 5% of primary bone tumors and approximately 18% of benign bone tumors.1 Typically seen in patients aged 20 to 40 years, GCTs demonstrate a slight female predominance.2,3 The tumors are named for their appearance under a microscope. Specimens demonstrate a mix of mononuclear stromal cells and abundant giant cells in a uniform distribution. The presence of giant cells is nonspecific, however, as they can be seen in many skeletal disorders, neoplastic and non-neoplastic.4
GCTs tend to form in the ends of long bones and rarely occur prior to fusion of the physeal growth plates.5 The most common site is the distal femur near the knee joint.1 Other locations include the proximal tibia; the distal radius; the proximal femur; the proximal humerus; and the lower back, more commonly in the sacrum than the vertebral body. In the long bones, the tumor generally begins to form in the metaphysis and spreads to involve the epiphysis. Although typically considered a benign lesion, approximately 5% of GCTs are malignant and can metastasize, usually to the lungs.6 Metastasis is a rare occurrence and usually the result of malignant transformation of the tumor following radiation treatment.
At presentation, patients typically will have tenderness, progressively worsening pain, and occasional swelling or decreased range of motion in the area of interest. A pathologic fracture may be found in as many as 10% of patients at the initial evaluation.5 Sometimes a mass is palpable.
The diagnostic test most commonly used to evaluate a patient presenting with pain or other symptoms in a joint or bone is radiography. Radiographs of GCTs may demonstrate a lytic lesion with a "soap bubble" appearance. Expansion of the affected bone may or may not be visible at the lesion site. GCTs are usually subarticular in location, often coming to within 1 cm of the articular surface. A narrow zone of transition exists at the interface of the lesion with normal bone. GCTs typically lack periosteal reaction or a sclerotic rim. The usual size at discovery is 5 to 7 cm.
MRI is commonly used to further evaluate tumors and may reveal associated soft-tissue changes, subchondral breakthrough of the tumor, marrow changes, and intra-articular extension. On T1-weighted images, GCTs can have low to intermediate signal intensity. Areas of high signal intensity may indicate hemorrhage. On T2-weighted spin echo images, the signal may be of high intensity. Cystic areas often have high signal intensity, and fluid-fluid levels may be evident.
CT is generally not used to evaluate GCTs unless they are located in the spine or sacrum, as radiographs are less helpful in these regions. CT is also used for periodic follow-up of patients with GCT, in order to look for lung metastasis.
Radionuclide bone scanning will show increased radiotracer uptake in the area of the bone lesion, but this is not specific for GCT and therefore not useful for diagnosis in this instance.
The differential diagnosis of a GCT can include aneurysmal bone cyst, chondroblastoma, brown tumor of hyperparathyroidism, telangiectatic or fibrogenic osteosarcoma, osteoblastoma, and giant cell reparative granuloma. Biopsy is typically performed. Many aneurysmal bone cysts are associated with other bone lesions; almost 40% of these are GCTs. When viewed microscopically, aneurysmal bone cysts contain giant cells around vascular channels or hemorrhage. Chondroblastomas are typically seen in patients in their second decade. These lesions are usually located in the epiphyses of the immature skeleton and may contain calcifications. Microscopically, they contain few giant cells. Brown tumor of hyperparathyroidism may appear histologically similar to GCT, but patients with brown tumor often have elevated serum calcium levels and skeletal changes on radiography at other sites. Osteosarcomas can be difficult to distinguish from GCT. On microscopic examination, the former contain malignant cells and tend to demonstrate a focal distribution of giant cells. Osteoblastomas are more commonly seen in the diaphysis of long bones and in the vertebral column. Giant cell reparative granuloma is more common in the maxilla and mandible.
Surgery involving curettage and bone grafting or placement of bone cement is the most common treatment of GCT. The recurrence rate following curettage and bone grafting is high, at approximately 40%.6 Recurrence is usually within 2 years after treatment and can be decreased with the use of bone cement. Utilization of a high-speed burr and adjunctive measures, such as application of phenol or liquid nitrogen during surgery, can reduce the recurrence rate even more.
Radiation therapy is usually reserved for patients in whom surgery cannot be performed safely or effectively. Malignant transformation of the tumor may result. Embolization of the blood vessels
is reserved for difficult cases that are not amenable to surgery. Occasionally, treatment requires large resection of the tumor with extensive reconstruction of the affected area. Even when GCT has metastasized to the lungs, the prognosis remains good following removal of the metastatic lesion(s). JAAPA
Julie Vajnar is the department editor for Diagnostic Imaging Review and practices in a radiology group at North Oaks Health System, Hammond, Louisiana. She has indicated no relationships to disclose relating to the content of this article.
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