DOI:10.2214/AJR.06.5024
AJR 2006; 186:1198
© American Roentgen Ray Society
Comment on Chest Radiograph as a Triage Tool
Eric N. C. Milne
University of California Irvine Irvine, CA
I read with considerable interest the article by Daftary et al.
[1] on the "Chest
Radiograph as a Triage Tool in the Imaging-Based Diagnosis of Pulmonary
Embolism" and must apologize for the delay in sending this letter. The
authors' approach appears to be founded on the belief that there is no
ventilation shift associated with a pulmonary embolus. This concept is, of
course, very widely (almost universally) held and is the reason for the belief
that perfusion scans for the diagnosis of pulmonary embolism are not accurate
unless they are accompanied by a ventilation scan. There is, however, good
evidence that a ventilation shift does accompany a pulmonary
embolus.
Julius Comroe [2], the great
pulmonary physiologist, was the first to document this ventilation shift and
very recently, Pistolesi and Miniati
[3] have shown, based on the
same physiological findings, that the predictive accuracy of perfusion
scanning is increased and the percentage of indeterminate scans is
considerably reduced if a ventilation scan is omitted. The concept proposed by
Daftary et al. [1] that we
should not do a perfusion scan if the chest radiograph is abnormal is only
valid if one persists in believing that it is only pulmonary disease that
causes a ventilation shift. To compound this, the chest radiograph is in fact
normal in only 12% of pulmonary embolus cases. It is much more common for the
chest radiograph to show atelectasis or consolidation in the region of a
pulmonary embolus [4], and is
another reason not to reject perfusion scanning because the chest radiograph
is abnormal.
As long as the belief persists that pulmonary emboli are not accompanied by
a ventilation shift, and perfusion scans continue to be accompanied by and
interpreted in the light of the ventilation scan, ventilation/perfusion
scanning will remain a poor diagnostic imaging tool. I would suggest that
rather than using the chest radiograph to reduce the number of
ventilation/perfusion scans, it would be better to follow Pistolesi and
Miniati's [3] well-documented
approach and improve the accuracy of perfusion scanning by omitting the
ventilation scan. With the reduction in the number of indeterminate scans that
this approach provides there would be no reason to use the chest film for
triage.
References
- Daftary A, Gregory M, Daftary A, Seibyl JP, Saluja S. Chest
radiograph as a triage tool in the imagingbased diagnosis of pulmonary
embolism. AJR 2005;185
: 132-134[Abstract/Free Full Text]
- Comroe JH Jr. The main functions of the pulmonary circulation.
Circulation 1966;33
: 146-158[Free Full Text]
- Pistolesi M, Miniati M. Imaging techniques in treatment algorithms
of pulmonary embolism. Eur Respir J 2002;19
[suppl]: 28s-39s
- Worsely DF, Alavei A, Aronchick JM, et al. Chest radiograph
findings in patients with acute pulmonary embolism: observations from the
PIOPED study. Radiology 1993;189
: 133-136[Abstract/Free Full Text]
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