- Pictorial Review
- Open Access
Pulmonary fibrosis on the lateral chest radiograph: Kerley D lines revisited
© The Author(s) 2017
- Received: 31 May 2017
- Accepted: 7 July 2017
- Published: 7 August 2017
The retrosternal clear space (RCS) is a lucent area on the lateral chest radiograph located directly behind the sternum. The two types of pathology classically addressed in the RCS are anterior mediastinal masses and emphysema. Diseases of the pulmonary interstitium are a third type of pathology that can be seen in the RCS. Retrosternal reticular opacities, known as Kerley D lines, were initially described in the setting of interstitial oedema. Pulmonary fibrosis is another aetiology of Kerley D lines, which may be more easily identified in the RCS than elsewhere on the chest radiograph.
• The RCS is one of three lucent spaces on the lateral chest radiograph.
• Reticular opacities in the RCS are known as Kerley D lines.
• Pulmonary fibrosis can be seen in the RCS as Kerley D lines.
• Kerley D lines should be further evaluated with chest CT.
- Pulmonary fibrosis
- Lung diseases, interstitial
- Thoracic radiography
- Multidetector computed tomography
- Pulmonary emphysema
Diseases of the pulmonary interstitium are another type of pathology that can be identified in the RCS. Owing to its lucency, the RCS clearly illustrates reticular opacities that may be obscured in other regions of the chest radiograph. Kreel et al. (1975) first described reticular opacities in the RCS in the setting of interstitial pulmonary oedema before CT was readily available . They named these septal lines “Kerley D lines,” expanding upon Kerley’s initial characterization of A, B, and C lines on the frontal radiograph. Linear opacities in the periphery of the lung that extend to the pleural surface, Kerley D lines have the same appearance as the more familiar Kerley B lines, but in a different location (Fig. 1b).
We present a case-based review of pulmonary fibrosis detected in the RCS—analogous to Kerley D lines caused by interstitial oedema—with CT correlation.
Although high-resolution chest CT is the gold standard for evaluating interstitial lung disease, chest radiography is frequently the initial investigation, despite its limitations. A confident diagnosis of the aetiology of pulmonary fibrosis can be made in only 23% of cases on radiography , and up to 10% of patients with pulmonary fibrosis have a normal chest radiograph with normal lung volumes . Early interstitial lung disease may also be an incidental finding in patients with subclinical or undiagnosed fibrosis. This highlights both the difficulty and importance of detecting interstitial lung disease on chest radiography.
Although a lateral radiograph is not routinely performed at some institutions, nearly all of the outpatient chest radiographs at our institution include both frontal and lateral views. Many of our referrers request frontal and lateral radiographs as the initial work-up for interstitial lung disease prior to chest CT. We have found the lateral view to be a useful supplement to the frontal radiograph, particularly for evaluation of the RCS. In addition to occasionally being the only sign of interstitial lung disease on otherwise normal radiographs, the recognition of Kerley D lines can also boost the confidence of the radiologist who suspects but is uncertain about reticular opacities on the frontal view.
Kerley D lines were initially described in regard to interstitial pulmonary oedema in the RCS on the lateral chest radiograph. Pulmonary fibrosis is another potential source of Kerley D lines, which may serve as an early indicator of interstitial lung disease on an otherwise normal exam. In institutions where frontal and lateral radiographs are routinely performed in the initial work-up for pulmonary fibrosis, we suggest close inspection of the RCS. When Kerley D lines are identified and pulmonary fibrosis is suspected, a chest CT should be obtained for further evaluation.
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