RADIONUCLIDE IMAGING OF ACUTE PULMONARY EMBOLISM
Section snippets
CLINICAL DIAGNOSIS OF PULMONARY EMBOLISM
In the clinical evaluation of patients with established PE risk factors, clinical signs and symptoms were similar in men and women.47 The risk of PE does increase with age. Sedentary lifestyle, prolonged recovery phase following illness, congestive heart failure, malignancy, and increased hip fracture rates in the elderly are factors that increase the likelihood of PE.4, 19 The clinical findings of patients with suspected PE and no pre-existing cardiac or pulmonary disease were evaluated in a
VENTILATION-PERFUSION LUNG SCANNING IN PULMONARY EMBOLISM
The V/Q lung scan has been shown to be a safe noninvasive technique to evaluate regional pulmonary perfusion and ventilation. The technique has been widely used in the evaluation of patients with suspected PE.
PROSPECTIVE TRIALS
Data from multiple prospective and outcome-based large studies have reported on the efficacy of V/Q scanning in patients suspected of having acute PE.26, 27, 28, 30, 34, 45, 73 In a prospective study by Hull et al,27 874 patients suspected of having PE were enrolled. V/Q scan interpretations were grouped into three diagnostic categories: (1) normal; (2) non–high probability; and (3) high probability (mismatch defect involving at least 75% of a segment). The purpose of the study was to determine
INTERPRETATION CRITERIA
Several diagnostic criteria have been suggested for the interpretation of V/Q lung scans. In a study comparing the various interpretation algorithms, the PIOPED criteria had the highest likelihood ratio for predicting the presence of PE on pulmonary angiography. The PIOPED criteria, however, also had the highest proportion of V/Q scans interpreted as representing an intermediate probability of acute PE.72 Several revisions of the original PIOPED criteria have been made based on the observations
VENTILATION-PERFUSION LUNG SCANNING IN THE EVALUATION OF PULMONARY HYPERTENSION
Chronic pulmonary thromboembolism is a serious and potentially surgically treatable cause of PHT. It has been estimated that between 0.5% and 4% of patients with acute PE eventually develop chronic thromboembolic PHT.37 Unfortunately, the clinical features, laboratory investigations, and other noninvasive investigations are often unreliable in distinguishing chronic thromboembolic PHT from primary and nonthromboembolic secondary PHT. Evaluation with pulmonary angiography is usually required to
COMPUTED TOMOGRAPHY ANGIOGRAPHY IN PULMONARY EMBOLISM
Both spiral and helical CT angiography and electron beam CT have been used to visualize and diagnose PE directly.50, 51, 53, 66, 67, 69, 70 With spiral CT angiography data are continuously and rapidly collected as the patient moves through the gantry. Volumetric datasets of the entire lungs can generally be acquired during a single breath, which eliminates respiratory misregistration. Electron beam CT is less widely available and has superior temporal resolution but inferior spatial resolution
PULMONARY ANGIOGRAPHY IN PULMONARY EMBOLISM
Pulmonary angiography has remained the definitive gold standard test for the diagnosis or exclusion of PE. The angiographic diagnosis of acute PE in PIOPED was based on the identification of an intraluminal filling defect or the trailing edge of a thrombus obstructing a vessel. In patients who had angiographic evidence of PE, reader agreement among angiographers was noted to be 86% (331 of 383) of cases. In patients with angiograms interpreted as negative or uncertain, PE reader agreement was
SUMMARY
From the prospective and outcome-based studies that have been carried out in the past few years, the following conclusions regarding the diagnostic evaluation of patients with suspected PE can be made:
- 1
A normal V/Q scan interpretation excludes the diagnosis of clinically significant PE.
- 2
Patients with a very-low- or low-probability V/Q scan interpretation and a low clinical likelihood of PE do not require angiography or anticoagulation.
- 3
Patients with a very-low- or low-probability V/Q scan
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Address reprint requests to Daniel F. Worsley, MD, University of British Columbia, Division of Nuclear Medicine, Vancouver General Hospital, 899 West 12th Avenue, Vancouver, BC, Canada, V5Z 1M9. e-mail: [email protected]