Having a really hard time reading CXRs and telling whether I'm looking at effusions, infiltrates, infarction, etc. I've tried looking at some sites, but I think I'm just getting more confused. I think what I'm also missing is a fundamental understanding of the basic definitions of the different signs as they relate to CXRs. If anyone can help me out with either of these problems, or guide me to some resources that they found helpful for them, that'd be awesome.
Thanks
It helps if you understand 3 fairly simple things independently.
1. Air vs fluid on xrays: Air is black, fluid is white.
2. The normal CXR appearance: Normal lung markings, costodiaphragmatic recess, trachea, and mediastinal structures.
3. What's happening in x-diagnosis: For example pleural effusion = fluid, emphysema = lots of air, etc.
Infiltrates: In general, infiltrates can be either interstitial or intraalveolar. Obviously both types can coexist in one patient. Interstitial infiltrates will show up as linear opacities (white) because they are within the connective tissue areas. Intraalveolar infiltrates are said to be "fluffy", but basically if it doesn't look linear and it isn't an effusion, then it's intraalveolar infiltrate. So, how do you know it's not an effusion? Continue reading.
Effusions: In a standard AP CXR the patient is standing, and thus any effusion will settle at the lung base (due to gravity). Effusions are fluid. They can be transudative (nephrotic syndrome, liver cirrhosis, HF), exudative (pneumonia, lung infarction), or chylous/lymphatic (disruption of the thoracic duct by trauma/surgery or malignancy). You cannot tell what type of effusion it is based on the CXR alone. Anyway, back to the point. Effusions are fluid and fluid will be pushed down by gravity as far as possible. In the case of pleural effusion, this means into the costodiaphragmatic rescess. A normal CXR will have "sharp" and well-demarcated costodiaphragmatic rescesses (one on each side). The CD rescesses are extensions of the pleural space (recall that the pleural space extends further than the lung). Why do effusions obscure the rescess? Because there is fluid where there used to be air, and fluid is white and air is black. Can't see the rescess edges anymore because there is a bunch of white stuff blocking it from view.
Infarctions: I've seen less of these in class and I'm assuming that's because they are less common. Regardless, recall the general concept that all infarctions result in coagulative necrosis (except in the brain) that appear "wedge-shaped". Why are they wedge-shaped? Because the branching of vessels results in each vessel supplying a wedge-shaped area of tissue. So, an infarction on CXR will be a white area that looks similar to an infiltrate, except that it is wedge-shaped (rather than linear/interstitial or intraalveolar).
Pneumothorax: These can be difficult when you first start looking at them, but over time they become much easier to see. Say you have a left-sided pneumothorax. At first you might look at the CXR and think that the right lung is abnormal and full of infiltrates. But, if you look closer, you'll notice that the left-side actually is full of black space with no lung markings. The black space is air within the pleural space. Now if you shift your gaze more medially toward the mediastinum you'll see a strange white outline. That outline is the collapsed lung. In a tension pneumothorax you might even have a clue with the mediastinum and/or trachea being shifted to the contralateral side.
