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

Background: 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.

Methods: 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.

Results: 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.

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