The comet-tail artifact:: an ultrasound sign ruling out pneumothorax

Objective: Ultrasound artifacts arising from the lung-wall interface are either vertical (comet-tail artifacts) or horizontal. The significance of these artifacts for the diagnosis of pneumothorax was assessed. Design: Prospective clinical study. Setting: The medical ICU of a university-affiliated teaching hospital. Patients: We compared 41 complete pneumothoraces with 146 hemithoraces in 73 critically ill patients in which computed tomography showed absence of pneumothorax. Measurements: The anterior chest wall was investigated in supine patients using a portable device. The test was defined as positive for complete pneumothorax when only horizontal artifacts were visible, and negative when artifacts arising from the pleural line and spreading up to the edge of the screen (referred to as "comet-tail artifacts") were present. Results: The feasibility was 98 %. Ultrasound showed exclusive horizontal artifacts in all 41 analyzable cases of complete pneumothorax. In the pneumothorax-free group, "comet-tail artifacts" were present in 87 cases and exclusive horizontal artifacts in 56. Ultrasound as well as computed tomography showed anterior consolidation or anterior pleural effusion in three cases. Horizontal artifacts had a sensitivity and a negative predictive value of 100 % and a specificity of 60 % for the diagnosis of pneumothorax. Horizontal artifacts and absent lung sliding, when combined, had a sensitivity and a negative predictive value of 100 % and a specificity of 96.5 %. Conclusions: Ultrasound detection of the "comet-tail artifact" at the anterior chest wall allows complete pneumothorax to be discounted.