Article: B-lines: Transthoracic chest ultrasound signs useful in assessment of interstitial lung diseases
Hasan AA, Makhlouf HA. B-lines: Transthoracic chest ultrasound signs useful in assessment of interstitial lung diseases. Ann Thorac Med. 2014 Apr;9(2):99-103
Objective: To examine whether B-lines seen on ultrasound are useful in the assessment of interstitial lung disease (ILD).
Design: Analytic cross-sectional study
Inclusion Criteria: Patients with ILD
Methods: Patients with ILD were enrolled in this study after obtaining informed consent. Diagnosis was determined by clinical presentation coupled with blood work, PFTs and HRCT. A chest HRCT was obtained on each patient by the department of radiology at full inspiration in the same sequence of images every time. Each patient was also given a severity score based on HRCT to determine the extent of lung involvement. Finally, each patient received transthoracic lung ultrasound in the Department of Chest Diseases. The ultrasound was performed by a pulmonologist trained specifically in sonography of the chest, and four areas were identified: upper and lower anterior regions, and upper and basal lateral regions.
Results: A total of 61 patients with ILD were included in the study, with 30 (49%) cases of idiopathic pulmonary fibrosis, 4 (6.5%) with sarcoidosis, 8 (13%) with collagen disease, 9 (14.7%) with hypersensitivity pneumonitis and 10 (16.4%) with another pulmonary diagnosis. On HRCT imaging, 14 (23%) patients had ground glass opacities, 20 (32.8%) had reticular patterns, 12 (19.7%) had reticulonodular patterns, 2 (3.3%) had nodular pattern and 13 (21.2%) had honeycombing.
All patients had B-lines present on transthoracic pulmonary ultrasound, and every patient had more than 6 B-lines on their ultrasound findings. Furthermore, the distance between each adjacent B-line correlated with the severity of the HRCT scan. There was also a relationship between the distance of adjacent B-lines and pattern noted on HRCT. For example, when ground glass opacities were seen on HRCT, the ultrasound showed more B-lines and these B-lines were closer together. On the other hand, for HRCT scans that demonstrated reticular patterns or honeycombing, the B-lines were farther apart on ultrasound. In all HRCT patterns, though, the B-lines correlated with the severity score.
The distance between the B lines were classified as 7mm vs 3mm. Previous studies have reported that B lines that are wider (7mm) apart represent interlobular septal thickening. On the other hand, narrow or confluent B lines (less than 3mm apart) represent interstitial edema. In this study, they found an inverse correlation regarding the distance between B-lines and measurements of lung function including %FVC, TLC and DLCO.
This concept can be further understood based on the fact that the interalveolar septum distance is approximately 7mm, indicating that B lines occurring greater than 7mm apart represent a disease process occurring between the alveoli, whereas B lines occurring less than 7mm apart represent a disease process occurring within the alveoli. This explains why in early ILD, with inflammatory cells and edema within the alveoli, B lines are closer together. However in later ILD, with thickening and fibrosis of the interlobular septa, B lines are farther apart.
The inverse correlation of the distance between B lines indicates that the farther apart B-lines are in ILD is worse, whereas close together indicates the individual is earlier on in the disease process. This is in contrast from patients with CHF, for whom B-lines early in the disease course are father apart and as the disease progresses, the alveolar fullness (edema within the alveoli) leads to confluent B-lines and indicates severe CHF.
Takeaway: B-lines have a high utility to assess the presence of fluid and/or inflammation in the lungs. B-lines on transthoracic ultrasound correlate with HRCT findings of interstitial lung disease, and can be useful in diagnosis. The distance between B-lines can yield important information regarding severity of disease process. This is useful because bed side ultrasound is fast, inexpensive and non-invasive.
Author: Leah Goldberg, MS4