Tram-Line (Railroad Track) Sign

Broncho-pulmonary aspergillosis is an infectious complication seen in some patients with chronic asthma. McCarthy and colleagues’ (Brompton Hospital, London) related the radiographic findings of this condition in a review of 111 cases. Among the many signs they described in this article were tram-line shadows, parallel-line shadows, band-like (toothpaste) shadows and the gloved-finger shadow. Tram-line (or railroad-track) shadows were described as ‘Two parallel hair-line shadows extending out from the hilum in the direction of the bronchi, the width of the transradiant zone between the lines being that of a normal bronchus’ ¹ (Figure 1). Parallel- line shadows were ‘similar in site and direction to tram-line shadows, but the width of the trans-radiant zone between the lines is wider than that seen in a normal bronchus and, if a bronchogram is done, this bronchus will be seen to be dilated.’ ¹ Secretions in dilated bronchi caused toothpaste or gloved-finger shadows, thus, ‘A shadow some 2–3 cm long and 5–8 mm wide is aptly described as a band-like or a toodipaste shadow … A bandlike shadow with an expanded rounded distal end can be described as a gloved-finger shadow.’ ¹ Such shadows are not specific for broncho-pulmonary aspergillosis. They can be seen in asthmatic patients without aspergillosis and in patients who have cystic fibrosis. Figure 1 Tram-line shadows. The distance between the lines is appropriate to that of a normal bronchus at the same level.” Case courtesy of Dr C. White, University of Maryland https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003076568/34c29fd5-5662-4e8f-b58c-badd7fa5d724/content/fig91_1_B.jpg"/>