Pulmonary vascular nodules: new sign of left lower lobe collapse in children.

Left lower lobe collapse can be suspected in children on a frontal chest film when three or more peripheral left upper lobe vessels are seen end-on along the left heart border. The peripheral vascular changes are mainly due to the backward and downward displacement of the hilus. This "vascular nodule sign" was evident in 25 (70%) of 36 cases of left lower lobe collapse. Its frequency in normals is less than 10% and may be accounted for by lordotic projection. Although not entirely specific, this sign, easily noticeable even on an underexposed film, should raise the possibility of left lower lobe collapse.