24. Imaging of bone metastases. Radiologic and nuclear medicine techniques.

Bone metastases are far more frequent than primary bone tumors. Bones are the third most common site of metastasis, after the lung and liver. They are often multiple rather than solitary.

The most frequent symptom of bone metastasis is strong bone pain and pathological fractures.

Etiology

These metastases often originate from:

• Breast cancer
• Lung cancer
• Prostate cancer
• Thyroid cancer
• Kidney cancer

Breast, lung and prostate account for 80% of cases.

Pathology

Metastases most frequently form osteolytic lesions (decreased bone density) of the bone, as does renal cell carcinoma and multiple myeloma. A notable exception is metastases from the prostate, which form osteoblastic lesions (increased bone density).

Diagnosis and evaluation

Radiography is low sensitivity for both lytic and blastic bone lesions, but it is quite specific. More than 50% of the trabecular bone must be destroyed for the lesion to be visible on radiography. The Codman triangle may be visible on x-ray.

CT and MRI have high sensitivity and specificity.

Bone scintigraphy and PET or PET/CT is very sensitive for bone lesions but is less specific than CT or MRI.

Codman triangle

Codman triangle is a radiography sign visible in case of rapidly growing bone lesions, where the lesion grows so quickly that the periosteum does not have time to ossify. The sign refers to a triangular elevation of the periosteum visible on the radiograph.

The sign is usually seen in:

• Osteosarcoma
• Ewing sarcoma
• Bone metastasis
• +++