How to Interpret a Chest X-Ray (Lesson 7 - Diffuse Lung Processes)

  this is the seventh LESSON in this series on interpreting chest x-rays and the topic is diffuse lung disease the learning objectives are first to be able to identify and know the differential diagnosis of Load lung volumes and hyperinflation second to be able to identify pulmonary edema as well as specific features that can help distinguish cardiogenic from non cardiogenic ideologies third to be able to classify interstitial processes based on their radiographic features and finally to be able to compare typical findings in alveolar and interstitial processes the first topic in this LESSON will be a very brief discussion of lung volumes so here is an x-ray which shows an example of reduced lung volumes we know this because 

 

when we count ribs there are only seven full posterior ribs seen above the diaphragm where normally there should be nine to ten when describing an x-ray with reduced lung volumes it is important to describe it specifically as such and never as quote poor inspiratory effort which is frequently done the reason for this is that as the x-ray interpreter unless you are physically present when the x-ray was taken you have no idea what the patient's inspiratory effort was like low lung volumes may be the first sign of otherwise occult disease of the lung interstitial of the diaphragms neuromuscular apparatus or thoracic wall mislabeling this x-ray as poor inspiratory effort risks missing an opportunity at an early diagnosis of these conditions having said that the most common etiology of reduced lung volume may in fact be poor inspiratory effort it may also be the consequence of a sub-optimally timed exposure it can obviously be seen in restrictive lung disease due to any of the aforementioned general mechanisms and finally it can be the consequence of unappreciated subharmonic effusions which were discussed in the last LESSON in this series in contrast to low lung volumes we can instead see hyperinflation which in my experience is less common there is no widely applied precise definition of hyperinflation on x-ray instead the term refers to a subjective impression that the total lung capacity is likely increased if measured by pulmonary function tests this subjective impression is based upon the number of ribs seen flattening of the diaphragms and the diffusely increased lucency of the lungs hyperinflation has a very short and specific differential diagnosis it is most commonly seen in COPD it can also occur occasionally in asthma but only during acute exacerbations for the remainder of this LESSON I'll be referring to the two classic radiographic categories of diffused lung capacities they are alveolar opacities often referred to as airspace capacities and interstitial opacities while I will be discussing the features which distinguish one category from another and discussing the subtypes of each in practice the distinction between alveolar and interstitial opacities is not easy it is a skill that entails much subjectivity requires much experience and typically shows significant interrelation a large part of these issues stems from the fact that few diffused lung diseases are completely limited to only the air spaces or to the interstitial many diseases which are classically alveolar such as pulmonary edema may also demonstrate typical interstitial changes and many diseases which are classically interstitial such as sarcoidosis may also demonstrate typical alveolar changes as a consequence many of the distinctions discussed during the rest of this LESSON are not always obvious and they may be a source of disagreement even between experienced healthcare professionals alveolar opacities are due to fluid accumulation within the alveoli and terminal bronchioles this fluid may be edema pus or blood opacities are hazy with poorly defined margins but can respect low bar boundaries unless diffuse differential diagnosis for most alveolar opacities can be divided into two main subtypes first is cardiogenic pulmonary edema which is that associated with an elevated pulmonary capillary wedge pressure which is a surrogate for elevated left-sided heart pressures in general this type of pulmonary edema can be seen in any cause of congestive heart failure this includes exacerbations of long-standing cardiomyopathy acute MI arrhythmia myocarditis or acute aortic or mitral regurgitation secondary to endocarditis then there is non cardiogenic pulmonary edema in which the wedge pressure is normal the clinical correlate to diffuse non cardiogenic pulmonary edema is the spectrum between acute lung injury and acute respiratory distress syndrome the distinction between these two is largely arbitrary and is based on the severity of a patient's hypoxemia as with heart failure a li and ARDS are not ideologies themselves but can be caused by a long and diverse list of pathologic conditions these include severe sepsis pneumonia including viral pneumonia from things like influenza aspiration pneumonitis pancreatitis severe burns post transfusion reaction near-drowning extreme elevation CNS catastrophe and inhalational injury in order to differentiate cardiogenic from non cardiogenic edema on x-ray there are five radiographic features which one can look for they are air Branca Graham's peribronchial cuffing curly lines cephalization and the bat swing pattern I'll talk about each one at a time first up our air Bronco Grahams since bronchi are relatively thin walled air filled structures surrounded by air filled alveoli they are usually not visible on x-ray however a pacification of alveoli adjacent to a bronchus results in the dark air field bronchi becoming identifiable against a white background in this example the patient has a pacification of the right lower lung zone probably the right middle lobe as we will discuss in the next LESSON if we zoom in on the pacification we can see an outline of a dark branching structure which are the bronchi visible bronchi are not only a manifestation of air Branca grams but also of peribronchial cuffing interstitial edema can accumulate a round bronchi making the bronchial walls thick this appears like a ring when seen in cross-section and like tram tracks when seen longitudinally here is an x-ray with a number of different findings if we zoom in again on the right mid-long zone we can see two ring shaped structures adjacent to one another which are bronchi seen in cross-section next are curly a and B lines curly a lines are diagonal on branching lines two to six centimeters long extending from the hilum they represent channels between peripheral and central lymphatics curly B lines are faint thin horizontal lines 1 to 2 centimeters long at the long periphery usually at the bases they represent inter lobular septa in general curly be lines are much more commonly seen and commonly referred to than curly a lines in this example if we zoom way in at the right lung base we can see the tiny faint horizontal curly B lines specifically indicating this patient may have mild heart failure the term cephalization refers to increase the visibility of pulmonary vessels at the lung apices as compared to the basis it is suggestive of increased left atrial pressure in this example if we compare the average density of the pulmonary vessels in the apices to the middling zones we can see that they are more prominent in the apices unfortunately cephalization is highly subjective and has relatively poor interobserver agreement limiting its utility as a radiographic distinguishing feature of pulmonary edema lastly is the so called bat swing pattern of a pacification sometimes referred to alternatively as a butterfly pattern or angel's wings this refers to bilateral parry higher concentration of a pacification this is seen predominantly in cardiogenic pulmonary edema but also in some types of pneumonia particularly viral pcp and aspiration it can be seen in inhalational injury pulmonary alveoli proptosis and in pulmonary hemorrhage so how do these radiographic features help distinguish cardiogenic from non cardiogenic pulmonary edema in cardiogenic edema the cardiac size is typically enlarged while in non cardiogenic edema it is typically normal in cardiogenic edema the regional distribution of opacities is relatively homogeneous while it is relatively patchy and non cardiogenic edema air Branca Graham's are common only in non cardiogenic edema while peribronchial cuffing is common only in cardiogenic edema and concurrent pleural effusions and curly be lines are more common in cardiogenic although not listed explicitly in this chart a batwing pattern to the pasady s is most consistent with cardiogenic edema though it may be seen with some specific ideologies of non cardiogenic edema as listed on the previous slide finally cephalization has historically been associated with cardiogenic edema however the subjectivity and lack of interest regarding this finding limits its usefulness if you recall back to near the beginning of this LESSON you may remember that alveolar opacities can be caused not just by edema in the alveoli but also by pus or blood therefore ideologies that diffuse alveolar opacities without edema include multi lowbar pneumonia and diffuse alveolar hemorrhage I'll now move on to discuss interstitial opacities there are several subtypes of interstitial opacities based upon radiographic appearance the first are reticular opacities which essentially means there are too many lines this can create a lace-like or net-like appearance another subtype is nodular opacities which means there are too many dots or nodules for diffuse interstitial disease the nodules are almost always less than one centimeter in size if the nodules are all less than two millimeters it is sometimes referred to as a miliary pattern due to the fact that someone a long time ago thought the nodules look like millet seeds finally our reticular nodular opacities which means there are too many lines and too many dots so here's an example of a reticular pattern that is too many lines and here is a nodular one and the last here are diffused particular nodular capacities the differential diagnosis of diffused interstitial opacities is very large and is generally difficult to place into categories of groups other than those diagnoses which cause a predominant reticular pattern and those which cause a predominant nodular pattern almost any cause of interstitial opacities can lead to a reticular nodular pattern those diseases which cause a predominantly reticular pattern of the fuchsia pass ''tis include idiopathic pulmonary fibrosis connective tissue disease atypical pneumonia such as that caused by mycoplasma the idiopathic interstitial pneumonias of which there are several histologic subtypes which cannot be distinguished on plain radiographs asbestosis chronic aspiration pulmonary drug toxicity sarcoidosis chronic hypersensitivity pneumonitis Langerhans cell histiocytosis and lymphangitis carcinomatosis as I said the differential diagnosis is very long in some cases there may be subtle clues pointing towards one diagnosis over others such as the presence of pleural plaques suggesting a particular pattern is due to a space no sis however for the most part most of these diseases are indistinguishable from one another on plain radiographs when it comes to the causes of diffused interstitial opacities that cause a predominantly nodular pattern these can be broken down into those with nodules under two centimetres and those with nodules over two centimetres provided one realizes that this cutoff is far from absolute those diseases causing small nodules include miliary tuberculosis fungal infections silicosis coal workers pneumoconiosis and sarcoidosis those which caused medium and large nodules include metastatic cancer subacute hypersensitivity pneumonitis lymphoma sarcoidosis granulomatosis with polyangiitis and rheumatoid nodules you probably notice that sarcoidosis has shown up on all three lists which is because sarcoidosis has a wide variety of manifestations in the lung along with causing either reticular or nodular interstitial patterns sarcoidosis can also cause alveolar opacities and is best known radiographically as a cause of prominent hilar lymph adenopathy I'll close this LESSON with a summary of a comparison between alveolar and interstitial opacities alveolar opacities showed low bar or segmental distribution unless they are diffuse or in the bats wing pattern while interstitial opacities do not respect low bar or segmental boundaries the margin of alveolar opacities is relatively hazy while interstitial opacities have a relatively sharp margin alveolar opacities may contain air Branca Graham's if they are caused by non cardiogenic pulmonary edema while interstitial opacities are generally devoid of them alveolar opacities can change rapidly over time with an ability to appear and disappear within hours while interstitial opacities generally evolve much more slowly and finally alveolar opacities are often described in highly subjective terms such as fluffy cotton wool like or cloud like interstitial opacities are described in the semi objective terms a particular nodular or reticular nodular that concludes this LESSON on diffused lung processes the next LESSON in this series will cover focal lung processes you