Background
Diffuse comet-tail B-line artifacts in lung ultrasound are a sign of alveolar-interstitial syndrome, but isolated transthoracic scans positive for B-lines (multiple B lines or B+) could be detected in other conditions. The aim was to assess the prevalence and distribution of this sonographic sign in patients with normal lung or isolated alveolar consolidation in chest radiography.
Material and Method
Two hundred seventeen patients consecutively admitted to this emergency medicine unit with any diagnosis and without radiographic or clinical evidence of diffuse interstitial syndrome were analyzed. Each patient underwent chest radiography and lung sonographic examination with four anterolateral chest scans per side.
Results
Of the 1736 sonographic scans performed, 13.2% were positive for the B+ pattern. Positive scans significantly corresponded to laterobasal areas or radiographic opacities due to lung alveolar consolidations (p<0.005). Twenty percent of the laterobasal scans of 145 patients with radiologically normal lung were positive. The negative predictive value of B+ was 83.9% (95% confidence interval: 78.2-89.7%), with a specificity of 90.3% (95%CI: 85.5-95.1%) for predicting any localized radiographic pulmonary opacity.
Conclusions
B+ scans can be detected in the chest areas surrounding an isolated alveolar consolidation and in the laterobasal scans of a radiographic normal lung. These features should always be considered when lung ultrasound is performed to rule out the alveolar-interstitial syndrome in an emergency setting. Moreover, B+ patterns have a satisfactory negative predictive value for radiographic lung opacities, which could have added diagnostic value in the ED evaluation of dyspneic patients.

Keywords: Pneumonia - ultrasonography, Pulmonary Alveoli - ultrastructure, Lung Neoplasms - ultrastructure, Lung Diseases, Interstitial - ultrasonography, Lung - ultrasonography, Syndrome, Artifacts