Role of Bone Scintigraphy in Bone Metastases

Pathophysiology: accumulation of tracer at sites of reactive bone formation

False-negative scan: very aggressive metastases

False-positive scan: degeneration, healing fractures, metabolic disorders

Baseline bone scan:

1. high sensitivity for many metastatic tumors to bone (particularly carcinoma of breast, lung, prostate); 5% of metastases have normal scan; 5–40% occur in appendicular skeleton
2. substantially less sensitive than radiographs in infiltrative marrow lesions (multiple myeloma, neuroblastoma, histiocytosis)
3. screening of asymptomatic patients
   • useful in: prostate cancer, breast cancer
   • not useful in: non–small-cell bronchogenic carcinoma, gynecologic malignancy, head and neck cancer

• multiple asymmetric areas of increased uptake
• axial >appendicular skeleton (dependent on distribution of bone marrow); vertebrae, ribs, pelvis involved in 80%
• superscan in diffuse bony metastases

Follow-up bone scan:

• stable scan = suggestive of relatively good prognosis
• increased activity in:
  1. enlargement of bone lesions / appearance of new lesions indicate disease progression
  2. “healing flare” phenomenon (in 20–61%) = transient increase in lesion activity ← healing under antineoplastic treatment concomitant with increased sclerosis, detected at 3.2 ± 1.4 months after initiation of hormonal / chemotherapy, of no additional favorable prognostic value
  3. avascular necrosis particularly in hips, knees, shoulders caused by steroid therapy
  4. osteoradionecrosis / radiation-induced osteosarcoma
• decreased activity in:
  1. predominately osteolytic destruction
  2. metastases under radiotherapy; as early as 2–4 months with minimum of 2000 rads

DDx: pulmonary metastasis (SPECT helpful in distinguishing nonosseous lung from overlying rib uptake)