Whole body bone scintigraphy is used in the initial staging and follow-up of cancer patients. Distinguishing benign from malignant lesions may pose a diagnostic dilemma in patients with known malignancies but no known metastases (21,22). Jacobson et al. studied the bone scintigrams of cancer patients and found metastatic disease in 11% of patients with one new skeletal lesion and in 24% of patients with two new lesions (21). Follow-up bone scintigraphy showed an interval increase in activity in most patients with metastatic disease, whereas benign lesions usually remained either unchanged or showed less activity. Benign degenerative changes in the spine showed increased activity either permanently or for extended periods of time. Correlative radiography is routinely used to evaluate new lesions seen on bone scintigrams of cancer patients. Malignancy is effectively excluded when radiographs show a corresponding benign lesion. However, normal radiographs do not exclude a malignancy (22).
Coakley et al. studied solitary spinal lesions on planar bone scintigraphy and found that the location of the lesion is helpful in distinguishing benign from malignant disease (23). Lesions projecting beyond the vertebral body surface were all benign. Increased uptake extending diffusely through a vertebra, but not extending outside the lateral spinal margin, was a nonspecific finding and seen in patients with osteoporotic compression fracture, malignant collapse, spondylolysis, and crush fractures. Increased uptake confined between the midline and lateral spinal margin was also a nonspecific finding and seen with both malignant involvement of the vertebrae and in apophyseal joint arthritis. In the Coakley study, the spinal level of the lesion also had prognostic significance. Eight of10 lesions in the thoracic spine were malignant, whereas only 10 of 32 lumbar lesions were malignant. Even-Sapir et al. studied the location of lesions of the lower thoracic and lumbar vertebrae with SPECT imaging and identified additional useful information distinguishing benign from malignant disease (24). Lesions confined to the apophy-seal joints and lesions projecting beyond the vertebrae body surface were all benign. Uptake in the vertebral body with contiguous uptake in the pedicle was caused by metastases in 83% of the patients (Fig. 3), whereas focal or diffuse uptake confined to the body was benign 89% of the time. Conversely, Rineartz et al. found that SPECT lesions confined to the vertebral body were benign only 64% of the time (25). In the Reinartz study, lesions affecting the pedicle had a high likelihood of malignancy (> 87%) while lesions involving the facet joints had a relatively low likelihood of malignancy (< 22%). Lesions confined to the spinous process were indeterminate for malignancy. Algra et al. studied metastatic patterns within
vertebrae using CT and found that vertebrae arch sites always had associated metastatic tumor in the posterior column of the vertebral body (26). He found a predilection of metastatic disease in the posterior column of the vertebral body which he postulated to be due to posteriorly located basevertebral veins providing a route for hematogenous spread of tumor into the vertebrae with subsequent arch lesions occurring from direct invasion.
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