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

Objective: Ultrasound artifacts arising from the lung-wall interface are ei ther vertical (comet-tail artifacts) or horizontal. The significance of the se 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 7 3 critically ill patients in which computed tomography showed absence of pn eumothorax. Measurements: The anterior chest wall was investigated in supine patients u sing a portable device. The test was defined as positive for complete pneum othorax when only horizontal artifacts were visible, and negative when arti facts arising from the pleural line and spreading up to the edge of the scr een (referred to as "comet-tail artifacts") were present. Results: The feasibility was 98 %. Ultrasound showed exclusive horizontal a rtifacts in all 41 analyzable cases of complete pneumothorax. In the pneumo thorax-free group, "comet-tail artifacts" were present in 87 cases and excl usive 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. Horizont al 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 anter ior chest wall allows complete pneumothorax to be discounted.