Institutionen för kirurgisk vetenskap / Department of Surgical Science
Abstract
Pulmonary embolism (PE) is an elusive diagnosis and none of the existing
imaging modalities have a 100% diagnostic specificity or sensitivity.
Pulmonary arteriography (PA) is the most specific test although the
improvement of computed tomography technique has made this a commonly
used method. Lung scintigraphy often gives ambiguous results. Fibrin
split products (D-dimer) are released into the blood in PE were elevated
levels can be measured. However, D-dimer levels are elevated in venous
thromboembolic (VTE) disease as well as in a number of other conditions.
The aims of this thesis were to evaluate different radiological methods
including pulmonary arteriography, lung scintigraphy and spiral computed
tomography for the diagnosis of acute pulmonary embolism and to study if
a clinical probability protocol or a simple blood test such as D- dimer
could improve the diagnostic accuracy.
Study I investigated the complication rate of PA in 707 patients. The
overall complication rate was 1.6%, which is lower than previously
reported.
Study II assessed the interobserver variations in PA in 170 patients and
compared the consensus results to a final outcome diagnosis. The mean
interobserver agreement was 89%, higher for central vessel emboli, lower
for peripheral locations.
Study III investigated if the use of a combination of a clinical and
scintigraphic protocol in relation to the final outcome could improve the
diagnosis in patients with clinical suspicion of acute PE. A low combined
probability yielded a negative predictive value (NPV) of 98%. The
positive predictive value (PPV) was 100% if the combined probability was
high.
Study IV compared the diagnostic accuracy of contrast medium enhanced
spiral computed tomography of the pulmonary arteries (s-CTPA) and a latex
agglutination D-dimer assay in patients with suspected acute PE by using
PA and clinical follow up as reference method. sCTPA had 95% NPV and 94%
PPV. If a cut off level of 0.25 mg/L was used the corresponding figures
for D-dimer were 92% and 63%.
Study V investigated if 441 patients with a negative s-CTPA and without
DVT symptoms, venous studies or anticoagulant treatment had a new episode
of PE during three months follow up. Only 0.9% of the patients had proven
PE during the follow up period.
To conclude, the results of our studies show that PA is a safe method
with good interobserver agreement and low complication rate. By applying
a model of combined clinical and scintigraphic probabilities for PE, the
diagnosis is ruled in when the combined probability is high, and ruled
out when the combined probability is low. However, nearly half of the
patients will still have an uncertain diagnosis if lung scintigraphy is
used as diagnostic method.
A low cut-off level of D-dimer can be used as a screening test to rule
out PE, but can not confirm the diagnosis. s-CTPA has a high diagnostic
accuracy when compared to PA. The overall results indicate that a
negative s-CTPA result safely can rule out the existence of clinically
significant, acute PE