Giant Cell Tumors of the Bone: Changes in Image Features after Denosumab Administration

Abstract

Purpose: To assess the clinical importance in the feature change in giant cell tumors of the bone (GCTB) after denosumab treatment, detected by MRI.

Methods: In 12 patients, MRI and CT of GCTB obtained before and after the treatment retrospectively compared. The tumor size, the signal intensity (SI) ratio between the solid part of the GCTB and muscle, cystic part size, gadolinium enhancement and apparent diffusion coefficient (ADC) value were measured on MRI. The bone formation in the tumor was observed on CT and X-ray.

Results: The mean number of denosumab injections was 19 ± 10. The follow-up period was up to 2 years. One case showed partial remission, while the other 11 cases were stable. A mean SI ratio on T₂-weighted image statistically significantly decreased from 3.9 to 1.9 after the treatment. A cystic component in the tumor was observed in five cases before the treatment, and the diameter of the cystic part decreased after the treatment in 80% of cases (4/5). All the tumors showed contrast enhancement on T₁-weighted image pre- and post-treatment (11/11). The averaged ADC values were 1.52 × 10^-3 mm²/s before and 1.44 × 10^-3 mm²/s after the treatment (P = 0.63). Bone formation in the tumor was observed in 58% of cases (7/12).

Conclusion: The decrease of SI ratio on T₂-weighted image, shrinkage of cystic part and bone formation should be regarded as the effectiveness of denosumab treatment despite of no substantial change in the tumor size.

Keywords: denosumab; giant cell tumor of bone; magnetic resonance imaging.

Fig. 1

Magnetic resonance images of tissues obtained from a 37 y/o male with giant cell tumors of the bone (GCTB) in the tibia. Images are shown before and after denosumab administration. (a) T₂-weighted image of a MRI showing GCTB exhibiting a cystic component in the proximal tibia. The tumor was 60 mm in size, including the cystic component. The cystic component was 43 mm in diameter. (b and c) On diffusion weighted image, the solid part of the tumor showed high intensity. On apparent diffusion coefficient (ADC) map (b = 1,000), the ADC value of the solid part of the tumor was 1.03 (×10⁻³ mm²/s). (d) T₂-weighted image after denosumab treatment showing that the tumor had decreased in size to 50 mm. The size of cystic component was 18 mm (double-headed arrow). (e and f) On diffusion weighted image, the solid part of the tumor showed high intensity. On ADC map (b = 1,000), the ADC value of the solid part of the tumor decreased to 0.66 (×10⁻³ mm²/s).

Fig. 2

Computed tomography and MRI of a 33 y/o male with giant cell tumors of the bone (GCTB) in the carpal bones. Images are shown before and after denosumab treatment. (a and b) The tumor exhibited a well-defined geographic lucent lesion in the carpal bones that was 25 mm in size. On T₂-weighted axial imaging, the tumor demonstrated well-circumscribed inhomogeneous hypo-intensity and a small cystic component (arrow). Computed tomography did not show bone formation in the tumor. (c) Both multinucleated giant cells and intervening mononuclear cells were observed in this photomicrograph. (d and e) On T₂-weighted axial imaging, the tumor exhibited inhomogeneous hypo-intensity with an unclear boundary. The small cystic component disappeared after treatment. The tumor had slightly decreased in size to 22 mm. Computed tomography revealed GCTB in the carpal bones and new bone formation within the tumor. (f) Intermixed bone and fibroblast-like spindle cells were observed instead of multinucleated giant cells and intervening mononuclear cells.