Usefulness of Tomographic Versus Planar Lung Scintigraphy in Suspected Pulmonary Embolism in a Daily Practice

Objectives: Lung scintigraphy is non-diagnostic in most patients suspected of pulmonary embolism when performed in planar mode. Tomographic mode could improve lung scan performance but has not been rigorously assessed. In this study we assessed the usefulness of tomographic mode in patients with a non-diagnostic lung scan scintigraphy. Methods: pulmonary embolism was diagnosed or ruled out in consecutive patients with a non-diagnostic lung scan by the combination of a 4-slices computerized tomography and a lower-limb ultrasonography. Results given by reading the tomographic mode in ventilation/perfusion lung scan were compared to final diagnosis. Results: 142 out of 392 consecutive patients with a non-diagnostic planar lung scintigraphy were included while 47 were excluded, 45 because of contra-indication to contrast medium and 2 because of non-optimal opacification of pulmonary arteries. Ninety-five patients were evaluated. Pulmonary embolism was diagnosed in 20 (21%) patients and ruled out in 75 (79%). Concordance with final diagnosis was found in 77/94 (82%) patients. Tomographic mode was non-diagnostic in 1 (1%) patient. Tomographic mode sensitivity/specificity/accuracy were 0.79/0.83/0.80 respectively. Negative predictive value was 0.94. Discordances were related to single sub segmental or non-occluding segmental thrombus. Conclusion: Tomographic mode is diagnostic in nearly all patients and agreement with final diagnosis is found in the majority. Its excellent negative predictive value enables to rule out pulmonary embolism. Discordances were related to single sub segmental or non-occluding segmental thrombus which prognosis value remains to be established.