Are occult pneumothoraces truly occult or simply missed?

Background: Nonradiologists typically diagnose pneumothoraces (PTX) based on a visible pleural stripe. PTXs not seen on supine AP chest radiographs (CXR), but appreciated on a computed tomographic (CT) scan, termed occult pneumothoraces (OPTX), are increasingly common. The purpose was to (1) determine whether perceived OPTXs were truly occult or simply missed and (2) address factors that contribute to the poor sensitivity of the supine CXR.

Methods: A previous study of severely injured patients (ISS >or =12) identified 44 patients with OPTXs. JPEG images of these CXRs were randomly arranged with images of 11 injured patients without PTXs (CT proven). Three unique groups of radiologists reviewed the images for signs of PTXs, and determined if a thoracic CT was subsequently required.

Results: Retrospective review identified only 12 to 24% of the OPTXs depending on radiology group. The kappa inter-observer agreement value was 0.55 to 0.56 (poor agreement). PTXs were most commonly identified via the deep sulcus sign (75-90%). CXRs were considered inadequate in 16 to 25% of OPTX images and in 0 to 18% of images without OPTXs. Thoracic CT scans were recommended in 18 to 33% of patients with inadequate CXRs, but 67 to 82% of patients with adequate CXRs.

Conclusions: Less than 24% of all OPTXs might have been inferred from subtle radiologic findings, such as the deep sulcus sign. The majority of OPTX cases (50-64%) did not warrant a CT scan based on other findings. Concern for an OPTX after severe trauma is a valid indication for thoracic CT.