Scintigraphic diagnosis of pulmonary embolism

The ventilation-perfusion scintigram, as the pivotal noninvasive diagnostic aid in detection of pulmonary embolism, is interpreted with respect to regional comparison of ventilation, perfusion and chest radiographic findings. Two segmental mismatched defects in areas with normal ventilation and no associated radiographic abnormalities are required for the diagnosis. Scintigraphic findings can be classified into four major categories: normal, low probability, intermediate probability and high probability for pulmonary embolism (Table 1). Subsequent diagnostic measures can be derived from a flow chart accordingly (Figure 1). Patients with low probability have favorable outcomes without treatment; in those with high probability anticoagulants should be used unless specific contraindications exist. In the case of indeterminate results, further imaging evaluation is necessary.