[Helical CT and perfusion scintigraphy: diagnosis of pulmonary embolus in the clinical practice]

The purpose of this study was to compare helical CT with lung perfusion scintigraphy (LPS) as the initial investigations of patients with suspected pulmonary embolism (PE).

A total of 54 patients with clinically suspected acute PE were studied retrospectively. Each patient was assigned a pretest clinical probability of acute PE (very likely, 90%; possible, 50%; unlikely, 10%). Within 72 hours of presentation, patients underwent LPS and contrast material-enhanced helical CT. Perfusion LS was classified following the PISAPED criteria as normal or near normal; abnormal consistent with PE or abnormal not consistent with PE. Helical CT studies were categorized as positive for PE, negative for PE or non-diagnostic. The standard reference was a consensus based on LS, helical CT and clinical outcome.

In 38 of the 54 patients, the results of LS a hCT were concordant, 13 with PE and 25 without. There were 4 indeterminate hCT. In 12 patients LS and hCT were discordant. There were 4 LS false negative; 2 with parenchyma damage and 2 chronic PE. There were 5 LS false negative; 3 extrinsic vascular compressions and one low clinical probability. There was 1 hCT false positive because of breathing artifact and 2 false negatives because of subsegmental emboli.

Accurate diagnosis of acute PE is possible combining perfusion scanning and clinical probability. Helical CT has added information in patients with discordant clinical probability and perfusion lung scan results. Helical CT demonstrated lesions other than PE considered responsible for the patient's symptoms, but it was insensitive to embolism of subsegmental branches.