Diagnostic accuracy of oblique chest radiograph for occult pneumothorax: comparison with ultrasonography

Abstract

Backgraound: An occult pneumothorax is a pneumothorax that is not seen on a supine chest X-ray but is detected by computed tomography scanning. However, critical patients are difficult to transport to the computed tomography suite. We previously reported a method to detect occult pneumothorax using oblique chest radiography (OXR). Several authors have also reported that ultrasonography is an effective technique for detecting occult pneumothorax. The aim of this study was to evaluate the usefulness of OXR in the diagnosis of the occult pneumothorax and to compare OXR with ultrasonography.

Methods: All consecutive blunt chest trauma patients with clinically suspected pneumothorax on arrival at the emergency department were prospectively included at our tertiary-care center. The patients underwent OXR and ultrasonography, and underwent computed tomography scans as the gold standard. Occult pneumothorax size on computed tomography was classified as minuscule, anterior, or anterolateral.

Results: One hundred and fifty-nine patients were enrolled. Of the 70 occult pneumothoraces found in the 318 thoraces, 19 were minuscule, 32 were anterior, and 19 were anterolateral. The sensitivity and specificity of OXR for detecting occult pneumothorax was 61.4 % and 99.2 %, respectively. The sensitivity and specificity of lung ultrasonography was 62.9 % and 98.8 %, respectively. Among 27 occult pneumothoraces that could not be detected by OXR, 16 were minuscule and 21 could be conservatively managed without thoracostomy.

Conclusion: OXR appears to be as good method as lung ultrasonography in the detection of large occult pneumothorax. In trauma patients who are difficult to transfer to computed tomography scan, OXR may be effective at detecting occult pneumothorax with a risk of progression.

Keywords: Diagnosis; Lung ultrasound; Oblique chest radiograph; Occult pneumothorax.

Fig. 1

a We previously reported a method to detect occult pneumothoraces by supine oblique chest radiography (OXR) without a CT scan. b X-ray beam is projected onto a film by this OXR method

Fig. 2

A typical case of occult pneumothorax diagnosed by OXR. This 58-year-old woman was involved in a head-on car accident and arrived with dyspnea, right chest pain. a Anteroposterior supine radiograph shows no abnormality. b OXR on the right clearly reveals a distinct visceral pleural line (arrowheads). c CT scan proves the existence of an occult pneumothorax on the right side. d Supine oblique chest radiographs could be easily performed in a trauma resuscitation area

Fig. 3

Occult pneumothorax size on CT scan classification by Wolfman et al. [15]. Minuscule pneumothorax is defined as a thin collection of air up to 1 cm thick in the greatest slice and seen on no more than 4 cm length. Anterior pneumothorax is categorized as a collection of pleural air more than 1 cm thick, located anteriorly, not extending to the mid-coronal line, and which may be seen on 4 cm or more length. Anterolateral pneumothorax is defined as pleural air extending to the mid-coronal line at least

Fig. 4

False positive case of OXR. The overlap of a large breast causes a false positive. This look like a pleural visceral line on OXR (black arrowhead)