Imaging description

As with most bone tumors the location and radiographic appearance are the most important features in arriving at the correct diagnosis. The vast majority of giant cell tumors (GCTs) occur in long bones at subchondral locations especially the knee. On plain radiographs, a GCT appears as an eccentric, lytic, often expansile lesion without a sclerotic margin or radiographically discernable matrix. Cortical thinning or cortical break-through is invariably present, but these findings are better visualized by CT; a secondary ABC can also be associated with a giant cell tumor (Figures 90.1 and 90.2).

Two signs on bone scintigraphy can help in narrowing down the differential diagnosis: (1) increased radionuclide uptake at the periphery of the lesion and photopenia centrally (donut sign) (2) increased radionuclide uptake in the bone across the joint from the GCT.

On MRI, the solid components of GCT demonstrate low to intermediate signal intensity on both T1- and T2-weighted images in the majority of cases (Figure 90.3). The reason for this appearance has been attributed to the hemosiderin deposition, increased cellularity, and high collagen content.

Importance

Giant cell tumor (GCT) is a fairly common bone tumor accounting for about 4–9%of all bone tumors and 21%of all benign bone tumors. Females are slightly more affected than males; however lesions in younger patients and those involving the spine demonstrate a higher female predilection. Although GCT is classified as a benign, solitary tumor, it can behave as a locally aggressive lesion with a recurrence rate of 30–50%, and less than 5%become malignant; a smaller percentage of GCT can be multicentric. Giant cell tumor typically occurs in mature young adults between the third and fourth decade.