Kerley B lines in the lung apex - a distinct CT sign for pulmonary congestion

The purpose of this study was to establish a new computed tomography (CT) sign for pulmonary congestion (Kerley B lines in the lung apex in patients with cardiac or renal insufficiency) and to find the best signs to differentiate between pulmonary congestion and interstitial lung disease (ILD).

180 consecutive patients undergoing CT were retrospectively included: 43 patients with cardiac, 17 with renal and 30 with mixed cardiac/renal insufficiency. In addition, we selected 90 patients with known ILD (usual interstitial pneumonia and nonspecific interstitial pneumonia). The cases were retrieved by means of a full text search of radiological reports and electronic patient files. The cardiothoracic ratio and diameters of the superior and inferior vena cava were measured. Pleural effusion, peribronchial cuffing, Kerley B lines (interlobular septa), ground glass opacity (GGO) and consolidation were analysed for prevalence, distribution and quantity (1 to 3). Fisher’s exact and Mann-Whitney-test were applied using Bonferroni correction.

Kerley B lines in the lung apex were present in 81% and 76% of the cardiac and renal groups, respectively, which was significantly more than in the ILD group (26%, p <0.0001). In the insufficiency group, Kerley B lines were distributed more homogenously throughout the lungs compared with the ILD group in which they increased in amount from 32% in the upper lobe to 90% in the lower lobe. The septal lines were thinner in the ILD than in the insufficiency group (p <0.0001). Peribronchial cuffing was significantly more frequent in the cardiac group (67%) compared with the renal group (29%, p = 0.040) and the ILD group (0%, p <0.0001). Other pulmonary congestion signs such as cardiothoracic ratio, enlargement of the superior and inferior vena cava and pleural effusion did not vary between the cardiac and the renal groups but were significantly lower in the ILD group. However, ILD patients showed more GGO in the lower lobes (87%) then patients with insufficiency (42%, p <0.0001).

Interlobular septal thickening (Kerley B lines) in the lung apex is a specific sign for pulmonary congestion, although not exclusive (since in ILD there may be apical reticulation). In combination with peribronchial cuffing and increased cardiothoracic ratio, it allows differentiation between cardiac/renal insufficiency and pulmonary ILD.