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Letters to the Editor |
Department of Accident and Emergency Medicine, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, Hong Kong, China. e-mail: saukau@netvigator.com
Editor:
I read with interest the article by Dr Rowan and colleagues in the October 2002 issue of Radiology regarding the use of thoracic ultrasonography (US) to detect traumatic pneumothorax (1). To my knowledge, their study is the first prospective operator-blinded study in the English indexed literature that demonstrates the accuracy of this technique, in comparison with computed tomography (CT) as the reference standard. As such, their study is appreciated as an important landmark. Our emergency department has also initiated research in this area to correlate the results of bedside US with those of chest radiography (2). Nevertheless, before we forge ahead with this US technique, two questions remain regarding its accuracy and reliability.
First, as Dr Rowan and colleagues (1) pointed out, there may be substantial bias in their study population, since only those patients who required thoracic CT were included. These patients were likely to have more severe injuries; hence, the pneumothoraces were likely to be large. Can the US technique be as accurate as it was shown to be in their study when applied to patients with smaller pneumothoraces? The authors’ explanation was that because their patients were excluded if they had been treated with chest tube thoracostomy prior to imaging, patients with large, clinically important pneumothoraces would have been excluded. Hence, they argued instead that the pneumothoraces detected with US in their study were "subtle and clinically ’silent’ at the time of diagnosis." Whether large or small, I am still uneasy about this selection bias in relation to pneumothorax size. It would be immensely helpful if data that described the sizes of the pneumothoraces of the patients studied were also reported. The size estimation, though unreliable with US, could have been quantified with thoracic CT.
Second, the technique of identification of comet tail artifact, as described in their study, is not accepted by some authorities. According to McGahan et al of the University of California Davis Medical Center (3), it is the presence of comet tail artifact (not the absence, as described by Dr Rowan and colleagues) that is diagnostic of pneumothorax. It appears that a difference in the definition of comet tail artifact is responsible for this discrepancy (4,5). Until the scientific community has reached consensus on this issue, the mention of comet tail artifact in this respect in academic literature may be confusing.
The study of Dr Rowan and colleagues has encouraging results for the use of thoracic US in the detection of pneumothorax in trauma patients. Before this technique can be widely acceptable and applicable, however, more research is needed, especially to address the above two questions.
REFERENCES
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