Occult pneumothoraces in patients with penetrating trauma: Does mechanism matter?

Background: Supine anteroposterior (AP) chest radiography is an insensitive test for detecting posttraumatic pneumothoraces (PTXs). Computed tomography (CT) often identifies occult pneumothoraces (OPTXs) not diagnosed by chest radiography. All previous literature describes the epidemiology of OPTX in patients with blunt poly-trauma. Our goal was to identify the frequency of OPTXs in patients with penetrating trauma. Methods: All patients with penetrating trauma admitted over a 10-year period to Grady Memorial Hospital with a PTX were identified. We reviewed patients' thora-coabdominal CT scans and corresponding chest radiographs. Results: Records for 1121 (20%) patients with a PTX (penetrating mechanism) were audited; CT imaging was available for 146 (13%) patients. Of these, 127 (87%) had undergone upright chest radiography. The remainder (19 patients) had a supine AP chest radiograph. Fifteen (79%) of the PTXs detected on supine AP chest radiographs were occult. Only 10 (8%) were occult when an upright chest radiograph was used (p < 0.001). Posttraumatic PTXs were occult on chest radiographs in 17% (25/146) of patients. Fourteen (56%) patients with OPTXs underwent tube thoracostomy, compared with 95% (115/121) of patients with overt PTXs (p < 0.001). Conclusion: Up to 17% of all PTXs in patients injured by penetrating mechanisms will be missed by standard trauma chest radiographs. This increases to nearly 80% with supine AP chest radiographs. Upright chest radiography detects 92% of all PTXs and is available to most patients without spinal trauma. The frequency of tube thora-costomy use in patients with overt PTXs is significantly higher than for OPTXs in blunt and penetrating trauma.