|Year : 2020 | Volume
| Issue : 3 | Page : 236-239
Chest radiographs in the acute setting-collapse and consolidation
Emma St Joseph
Department of Radiology, Basildon and Thurrock University Hospitals NHS Foundation Trust, Basildon, United Kingdom
|Date of Submission||03-Mar-2020|
|Date of Decision||18-Apr-2020|
|Date of Acceptance||19-Apr-2020|
|Date of Web Publication||10-Jul-2020|
Dr. Emma St Joseph
Basildon Hospital, Nethermayne, Basildon, SS16 5NL
Source of Support: None, Conflict of Interest: None
Chest radiographs are extensively used yet surprisingly complex. Compressing the three dimensions of the patient into the two dimensions of the image, there is a lot of opportunities for overlapping shadows to trip up the unwary and obscure diagnoses. Lobar collapse and lobar consolidation can usually be identified and distinguished as distinct diagnoses. The silhouette sign is king; ask “what can be seen?” and “what cannot seen (that should be seen)?”
Keywords: Chest radiograph, chest X-ray, collapse, consolidation, silhouette
|How to cite this article:|
Joseph ES. Chest radiographs in the acute setting-collapse and consolidation. Curr Med Issues 2020;18:236-9
| Introduction|| |
A chest radiograph is one of the most widely performed radiological examinations in hospitals worldwide, useful in managing patients presenting with anything from scrub typhus to tuberculosis to trauma.,,, Yet the interpretation of a chest radiograph can be very difficult, and even the most experienced of chest X-ray readers can face challenges. When all of the many and varied structures inside a three-dimensional patient's chest are compressed into the two-dimensional world of chest radiography, the superimposition of all of these structures conspires to confuse and confound the unwary. Even armed with all the relevant clinical information pertaining to the patient in question, anyone can interpret a chest radiograph badly; it takes skill and practice to interpret them well.
Yet by approaching each pathology in a mechanical way, it is possible to develop a personal schema to deploy as a safety net to identify most pathologies.
In this article, we look at consolidation and collapse, but in both instances, it is the silhouette sign,, (pronounced: Sil-oh-wet), which holds the key to diagnosis. Understanding why this sign works is as simple as understanding why the child's game of hand shadow puppets works; you cannot tell where one hand ends and another begins because the resultant shadow is a composite of the individual silhouettes. When we look at a chest radiograph, the same is true; the only structures which we can appreciate are those where there is a density difference between the two structures. If two adjacent structures have the same density (for example, a consolidated lung lobe and the heart), then we cannot see where one begins and the other ends.
| Consolidation|| |
When the air in the lung is displaced by the presence of pus or inflammatory exudate, the affected alveoli become as dense as the abdominal organs or soft tissues of the mediastinum. In the case of lobar pneumonia, the structures adjacent to each lobe become obscured (the term “loss of clarity” is used). These are depicted in [Figure 1] (Consolidation © Medical Exam Prep). To establish which lobe has been affected, decide:
If only part of a lobe is affected, it may be that the features described above are incomplete. Similarly, bronchopneumonia is seen as bilateral patchy areas of opacification, typically affecting the lung bases more than the apices.
| Collapse|| |
Triangular-shaped opacities are seen in all collapses (with the exception of the left upper lobe). They result from the compression (also termed volume loss) of the lung parenchyma within the collapsed lung, which occurs when air distal to the point of obstruction is absorbed. Other secondary signs of volume loss may also be noted:
- Mediastinal shift towards the pathological side
- Bronchovascular and rib crowding
- Hemidiaphragm elevation.
To pinpoint the precise lobe, it is useful to remember how each lobe behaves when collapsed. This is summarized in [Table 2] and [Figure 2] (Collapse © Medical Exam Prep) and depicted in [Figure 3] (Lobar collapse© Medical Exam Prep).
The diagnosis of a lobar collapse on a radiograph is, of course, only half the story. In some instances, the underlying cause of the collapse may be discernible on the same film (e.g., radioopaque foreign body), but in many others, it may not be evident.
There are three different categories of underlying diagnosis behind every case of collapse. The cause can be luminal, mural, or extrinsic to the affected bronchus. Luminal causes (such as aspirated foreign bodies, or mucus plugging) may be managed acutely, but mural causes (such as a bronchogenic tumor) or extrinsic causes (such as compression from an adjacent mass) are unlikely to be solvable with any degree of rapidity.
| Pearls and Pitfalls|| |
Satisfaction of search
This phenomenon is well known and a source of great frustration to many. Once one pathology (perhaps the one suspected when the radiograph was suggested) has been located, it is all too easy to relax and enjoy the sensation of puzzle pieces fitting nicely together. Unfortunately, if medicine were that easy, then doctors would not be needed. Our job is not to find the obvious, and it is to not allow the obvious to blind us to the possibility of additional findings. The learning point here is that having made a diagnosis, keep looking.
There are many different areas within an adult chest radiograph where pathology can play hide-and-seek all too effectively. When looking at the chest radiograph of a patient, as well as targeting our viewpoint to the expected clinical diagnosis (as based on the history and examination findings of the patient), a practiced physician will develop a schema or safety-net designed to “catch” all manner of other diagnoses which may be lurking. An easy mnemonic to use is “SPARKLE.”
- S = Subdiaphragmatic gas-hollow viscus perforation
- P = Pleural edges-pneumothorax
- A = Apices-a Pancoast tumor
- R = Retrocardiac-a hidden area, check the lungs and look for hiatus hernia
- K = Skeleton-bones, joints
- L = Lines and tubes-check placement, check for hidden pathologies
- E-Evidence of previous surgery-clips in the axilla or around the heart.
Compare with previous
This technique is woefully underused at times. When taking a history, we always seek to establish the temporal nature of a presenting complaint; how did it start, what was it like before, how has it changed. The same can be applied to chest radiographs. Previous chest radiographs (or other imaging) are a mine of information and immensely useful. Of course, even if they have been acquired, they may not be immediately available in the acute setting, but it is seldom wasted time to hunt them down where feasible.
The “normal” chest radiograph
Sometimes, despite using all our faculties and experience, a chest radiograph still seems “normal.” (Arguably there is no such thing as normal.) In such cases, where having expected a straightforward diagnosis, we find nothing to corroborate this, and there are a few strategies to move forward. Firstly and hopefully, obviously, check and re-check the details of the patient. Are you definitely sure you are looking at the right image of the right patient from the right date? Thus reassured, try zooming out. Instead of inching closer and closer to the screen, sit back and take in the image as a whole. It is remarkable how often the diagnosis will suddenly become apparent simply by taking in the view.
It's all about your point of view
Acutely unwell patients rarely pose flawlessly for the perfect “PA” inspiratory shot. Often films may need to be acquired in sub-optimal AP, semi-erect or fully supine position, and this can significantly adversely affect the diagnostic quality of the resultant image.
| Conclusion|| |
- Chest radiographs, although commonly performed, are extremely challenging to interpret and should be treated with caution. Compressing three dimensions into two causes near endless possibilities for overlapping structures
- That said, common pathologies can behave in common trends
- Consider: Shadows, pertinent positive, and pertinent negative findings for each image and always take the clinical context into consideration
- Use a list of review areas such as SPARKLE to make sure easily 'missable' pathologies are not missed
- Compare with previous were possible
- Beware the phenomenon of satisfaction of search
- If all else fails, zoom out.
The author is grateful to Medical Exam Prep for consenting to the use of their images in this article.
Financial support and sponsorship
Medical Exam Prep is a source of financial support for the author.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]