Computed tomographic assessment of the posterior junction line and its association with emphysema

Visualization of a posterior junction line (PJL) on chest x-ray is evidence for emphysema. The correlation between the assessment of the PJL on computed tomography (CT) and emphysema is less clear.

One hundred thirty-seven patients were identified with CT and pulmonary function tests (PFTs) performed within 3 months of each other in a University hospital. The width of the PJL was measured at 2 levels by a blinded investigator: superiorly at the superior border of the aorta and inferiorly 2 cm below the aortic arch. This was correlated to clinical and PFT data and to CT evidence of emphysema.

Narrowness of the junction line showed poor correlation with PFT findings of emphysema as assessed by forced expiratory volume in 1 second-forced vital capacity ratio and diffusing capacity of the lung for carbon monoxide percent predicted. The PJL also correlated weakly to CT emphysema severity scoring (r = 0.06; P < 0.002). The area under the receiver operator characteristic curve was 0.652, with maximum accuracy at a width of 1.3 cm.

Our data suggest that despite statistical correlation between the narrowness of the PJL and emphysema, its clinical use is limited.