The objective of this study was to identify the relationship between a dynamic lung artifact, the dynamic air bronchogram, within alveolar consolidation and the diagnosis of pneumonia vs resorptive atelectasis.This prospective study was undertaken within the medical ICU of a university-affiliated teaching hospital. The sample comprised 52 patients with proven pneumonia (pneumonia group) and 16 patients with proven resorptive atelectasis (atelectasis group). All patients had alveolar consolidation with air bronchograms on lung ultrasound, were mechanically ventilated, and received fibroscopy and bacteriological tests. The air bronchogram dynamic was analyzed within the ultrasound area of consolidation.The air bronchograms in the pneumonia group yielded the dynamic air bronchogram in 32 patients and a static air bronchogram in 20. In the atelectasis group, air bronchograms yielded a dynamic air bronchogram in 1 out of 16 patients. With regard to pneumonia vs resorptive atelectasis in patients with ultrasound-visible alveolar consolidation with air bronchograms, the dynamic air bronchogram had a specificity of 94% and a positive predictive value of 97%. The sensitivity was 61%, and the negative predictive value 43%.In patients with alveolar consolidation displaying air bronchograms on an ultrasound, the dynamic air bronchogram indicated pneumonia, distinguishing it from resorptive atelectasis. Static air bronchograms were seen in most resorptive atelectases and one third of cases of pneumonia. This finding increases the understanding of the pathophysiology of lung diseases within the clinical context and decreases the need for fibroscopy in practice.