Today's topic in this lecture series on chest x-rays will be atelectasis, lines, tubes, devices, and surgeries. The learning objectives are to be able to identify atelectasis and lobar collapse, to know the general mechanisms and etiologies of atelectasis, to be able to accurately identify lines, tubes, and devices, and assess for proper placement and complications, and to be able to identify evidence of prior cardiac surgery, including identification of prosthetic heart valves. Adalectasis is a loss of lung volume due to collapse of lung tissue. For anyone interested in where the unusual sounding word came from, it's derived from Greek, adales meaning incomplete, and ectasy which the most reliable appearing sources translate to mean area. Adalectasis can be classified based on either mechanism or on radiographic appearance.
The most common clinically relevant form of adalectasis is called obstructive adalectasis or sometimes resorptive adalectasis. The trigger for obstructive adalectasis is airway obstruction, which is then followed by gradual gas resorption within non-ventilated alveoli. Ideologies of obstructive adalectasis include tumor, mucus plug, foreign body aspiration, and external compression of an airway. Then there is nonobstructive atelectasis, which has four subtypes. Passive atelectasis occurs when there is disruption of the normal contact between the visceral and parietal pleura, which then allows the elastic recoil of the lung to pull itself inward.
This is seen in pleural effusions and pneumothoraces. Compression atelectasis is when a space-occupying lesion in the thorax physically compresses adjacent lung. This is seen in large tumors or an elevated diaphragm.
Adhesive atelectasis is when there is diminished surfactant production seen in infant respiratory distress syndrome, acute respiratory distress syndrome, and radiation pneumonitis. Finally, it's somewhat esoteric but cicatricial atelectasis is the consequence of severe parenchymal scarring seen in some cases of tuberculosis and idiopathic pulmonary fibrosis. When it comes to chest X-rays, classification based on appearance rather than mechanism may be more relevant.
There are four basic radiographic patterns. First is called linear or plate-like atelectasis. This occurs in a thin but wide fashion, most commonly with a plate of atelectasis occurring parallel to the diaphragm and or perpendicular to a pleural surface.
Somewhat unexpectedly, regions of plate-like atelectasis can cross lung segments and even lobes. It is most often seen in patients with poor diaphragmatic motion or acute pulmonary embolism. Next is round atelectasis. This occurs when there is an infolding of redundant pleura most often associated with asbestos exposure.
This can lead to a false appearance of a small lung mass, leading to an alternative name for it of adalactatic pseudotumor. The hint that a round opacity is adalactasis and not a tumor is seeing a thin, tail-like extension protruding away from the main opacity, particularly in a patient with known asbestos exposure. Then there is segmental adalactasis, in which an entire lung segment collapses.
This is generally not detectable on plain radiographs, and requires chest CT for visualization. Finally, there is lobar atelectasis, which I'll spend the next few minutes discussing. Lobar collapse is an extreme form of atelectasis, usually from airway obstruction.
We already learned about the etiologies of airway obstruction when I mentioned obstructive atelectasis a few minutes ago. There are some radiographic findings frequently seen in all anatomic variations of lobar collapse, including elevation of the ipsilateral hemidiaphragm, mediastinal shift towards the side of collapse, and the juxtaphrenic peak sign, particularly with upper lobe collapse. Here's an example of the juxtaphrenic peak.
Some sources report it's caused by traction on the inferior pulmonary ligament, however more recent journal articles describe it as the result of an inferior accessory fissure. I'll now go through what the collapse of each of the five lobes looks like. The right upper lobe usually collapses superiorly and medially. Common findings include a density in the upper medial right hemithorax and superior displacement of the right hilum and horizontal fissure.
Right middle lobe collapse usually has minimal impact on surrounding structures and may only be noticeable on a PA or AP film by its reduction of overall right lung volume. It's much easier to identify on the lateral film as a thin shadow overlying the heart. The right middle lobe is the most common of the five lobes to collapse. The right lower lobe usually collapses inferiorly and posterior medially.
The collapsed lobe forms a wedge-shaped opacity behind the right atrium. The oblique fissure is often more visible than normal as it gets oriented more parallel to the x-ray beam and may mimic an inferiorly displaced horizontal fissure. The left upper lobe collapses anteriorly. In about 50% of patients, the left upper lobe also collapses medially, while in the other 50%, a portion of the left lower lobe will get interposed between the collapsed upper lobe and the aortic arch.
This is called the Luftsickle sign, which is German for air sickle. Lastly, the left lower lobe usually collapses posterior medially and inferiorly. Common findings include a triangular opacity behind the heart, inferior displacement of the left hilum, and obscuring of the outline of the descending aorta.
Here's a film that most of us hope to never need to interpret. It's a total mess. When taking an x-ray, it's obviously important for the technologist to move as many lines out of the field as possible.
But unfortunately, as in this example, many lines, tubes, and wires may not be able to be moved. And also unfortunately, identification of lines and tubes and assessment of their position is essential in the care of critically ill patients. In other words, you may be put into a position where you will need to account for every single every line on a film like this. So let's tackle the various types one at a time.
First are central lines. The relatively informal term central line simply refers to an intravenous catheter that has been placed in a central vein. Most commonly this refers to either the internal jugular, subclavian, or femoral veins, the last of which hopefully won't be visible on a chest film.
So here's a photograph of what a conventional central line looks like externally. This one is in the right IJ. There's also something called a PICC line, which stands for Peripherally Inserted Central Catheter, which is usually introduced into a relatively large peripheral vein in the arm and fed upwards such that the tip is within the central venous circulation. What do these look like on x-ray?
Here's a right IJ line. Optimal placement of a central line should place the tip at the junction of the superior vena cava and the right atrium. A line inserted further than this risks triggering arrhythmias by poking the myocardium of the right ventricle.
A line inserted less than that means that the vasoactive medications won't be delivered directly into the central venous system and that a central venous pressure transduced at that location will not accurately reflect intravascular volume status. And here's a PICC line. The rule for optimal placement for PICC lines is the same.
Next up are pulmonary artery catheters, also called Swann-Gans catheters. A complete discussion of these is well outside the scope of this video, but in extreme brief, this is a catheter which is advanced from a central vein all the way into the pulmonary circulation. From a radiology standpoint, the most important thing to know is how to assess its position.
The catheter will typically come down from either the right IJ or left subclavian, make a counterclockwise 270 degree turn within the cardiac silhouette from the viewpoint of the observer, and end at the level of the hilum, no more than a few centimeters right of midline. In the case of this film, the poor combination of exposure and contrast makes only the distal end of the loop visible. A general rule of thumb is that the tip should be no more than 3cm from midline, or 1cm beyond the cardiac silhouette. If it's advanced further than that, there is significant risk of either pulmonary infarction or pulmonary artery rupture, the latter of which is a particularly catastrophic complication with a high mortality rate. Here's an endotracheal tube used to deliver oxygen-rich air and positive pressure during mechanical ventilation.
And here's an x-ray of a patient with one inserted into the trachea. Proper placement results in the tip being about 5 cm above the carina. What happens if it's placed too distally? In this example, the tip of the endotracheal tube is in the right main bronchus. This results in no ventilation to the left lung, and over a span of minutes to hours, total collapse of that side.
Next are nasogastric tubes. which as their name implies are flexible tubes which enter the patient via the nares and are advanced into the stomach. Here's an example x-ray.
It may be hard to see the tube at first until we adjust the contrast and brightness a bit and there is the radio-opaque tip. Proper placement of a nasogastric tube is confirmed by seeing that it descends through the thorax centrally, it crosses the diaphragm, Once below the diaphragm, it initially deviates to the left, and optimally, the tip should be at least 10 cm below the gastroesophageal junction. What can go wrong with placement of an NG tube?
Well consider this x-ray. In this case, instead of passing the tube into the esophagus on the way to the stomach, it was passed into the trachea on the way to the right lung. Well this can create airway resistance, and can lead to immediate respiratory difficulties, the greater risk is performing gastric lavage or worse inadvertently starting tube feeds on this patient. 20-30 cc of Jevidi or Ensure into this patient's lungs may be all that is necessary to trigger a horrible aspiration pneumonitis or full-blown ARDS. Always check a newly placed NG tube's position via x-ray.
Here's a chest tube in the right hemithorax which is a large caliber tube introduced into the pleural space for the purpose of either draining a complicated effusion or empyema or for treatment of a large pneumothorax. Here's an interesting device known as a port. It is a subcutaneous surgically implanted tiny reservoir which is connected to a catheter tunneled into the central venous system.
It has a similar purpose to a PICC line though it can stay in for much longer. and is thought to have lower rates of infection. It's most often used in oncology patients requiring ongoing chemotherapy.
And here it is on x-ray. And the last on the list of lines and tubes, although they aren't either, are two examples of telemetry electrodes and wires, which have a variety of appearances, but the identification of which is usually quite easy. I'll move on now to discuss some cardiac devices. There are about 6 or 7 which an internist should feel comfortable identifying. The most obvious are pacemakers, which can be single chamber or more commonly dual chamber.
Here's a dual chamber model on x-ray. I'll review the three key components. First, there is the big thing up near the shoulder.
This is formally called the generator, but occasionally referred to as the can by cardiologists. The relatively large and homogeneous structure within is the battery. The wires going from the generator to the heart are called leads. In this case one goes to the right atrium and the other to the right ventricle. A variation on this theme is the biventricular pacemaker.
In this case, in addition to a lead going to the right ventricle, there is also one that enters the coronary sinus in the right atrium and snakes its way through the coronary sinus to the left ventricle. On this example, the LV lead is unusually superior and unusually easy to see. In my experience, these films often look more like this one, in which you really need to struggle in order to see that left ventricular lead.
There's an ICD, or implantable cardioverter defibrillator, which can be used to shock the heart out of potentially fatal arrhythmias. The clue that this device is an ICD is that there are two relatively thicker segments of the lead, which are called the coils, and which are two of three potential ends of the defibrillation circuit, with the generator itself being the third potential end. This interesting thing that looks like either a metal flower or an outline of a sliced open lemon right in the center of the heart is a peripherally inserted atrial septal defect closure device. This is not a USB thumb drive in the patient's chest, but rather an implantable loop recorder which can be used to capture rare arrhythmias without the need for the patient to wear an external monitor at all times. And finally, what looks like plumbing equipment is actually an example of a left ventricular assist device or LVAD which is implanted adjacent to a failing heart, usually to buy a little time while the patient is on the waiting list for a heart transplant.
There are four important complications of cardiac devices visible on x-ray. The first is pneumothorax from the implantation procedure itself. We saw some examples of pneumothoraces in lesson 6. Next, also from the procedure, is cardiac perforation, in which a lead is literally advanced right through the myocardium.
This rare complication typically causes immediate life-threatening tamponade, in which the blood from the heart begins to leak into the pericardial space. Amazingly, for some reason, the patient in this example film seems to have escaped this problem at least temporarily. However, there will definitely need to be a cardiothoracic surgeon involved in this lead's removal. Another complication which doesn't happen immediately, but rather years after device placement, is called lead fracture, in which the lead essentially breaks in two. The location of this particular fracture, as the lead passes near the clavicle and the first rib, is probably the most common on account of friction against those bones.
The last complication is probably more interesting than it is common and is demonstrated here. If you look closely in the region of the generator, you may notice that the end of one of the leads, the right atrial lead in this case, has been pulled way back. How did this happen? Over months to years, possibly as an anxious habit, the patient has fiddled with the subcutaneous device in a repetitive pattern such that it has rotated around several revolutions within the pacemaker pocket in the chest wall.
This has pulled the right atrial lead back, which has coiled up behind the device. This is called twiddler's syndrome. Also visible in this x-ray are epicardial pacing leads, which function the same way as conventional pacing leads do, but which are placed by cardiothoracic surgeons at the time of either bypass or valve replacement surgery.
Speaking of cardiothoracic surgery, let's see some consequences of this on x-ray. Whether or not you realized it, you've already seen some examples of a sternotomy in this video. After the sternum has healed, all that remains are the sternotomy wires, each of which looks like a deformed paper clip which pierces the two sides of the sternum and then is twisted together. In this example, you can also see some surgical clips from a coronary bypass graft.
These wires and clips will stay in forever, and be of no consequence to the patient whatsoever. A more interesting example of cardiac surgery on x-ray are prosthetic heart valves. There are many different types of prosthetic valves, and it will be a very rare circumstance in which you will need to be able to distinguish them on x-ray, but if you can, you'll definitely look like the superstar during hospital rounds. The first widely implanted valves were the Star Edwards valve, which was a mechanical valve using a design called a caged ball. Sometimes the ball was radiolucent and sometimes it was radio-opaque.
It's rare to see these now. Although they are extremely durable, they also had a high tendency to form clots requiring INRs of 2.5 to 3.5 and are no longer implanted. A more recent design is the Bjork-Shiley, which is known as a tilting disc mechanical valve. And there are also bioprosthetic valves, which are made of animal tissue primarily.
Some bioprosthetic valves are visible only from a metal ring, while others such as the Carpentier-Edwards valve have a slightly more visible metal skeleton to which the radiolucent valve leaflets are attached. In this example, blood flow through that valve is in this direction. In addition to identifying the type of valve present, It can be occasionally necessary to identify the valve position.
The prosthetic valves most easily confused are the aortic and mitral. There are a couple of methods used to differentiate them. One method is to look at their profile on the PA film.
A valve that is end-on or in profile suggests an aortic position. One that is on face suggests a mitral position. Consider this x-ray with two bioprosthetic valves.
Which one is which? The one more superior and to the patient's right is more in profile than the other, which means that this is the aortic valve, while the other is more on face, so that's the mitral. This method does not work 100% of the time, but it's reasonably good. Also, in patients who have either mechanical valves or bioprosthetic valves, in which there is more than just a ring visible on x-ray, sometimes you can use the apparent direction of blood flow to guide your conclusions about which valves have been replaced. One last method to identifying the location of prosthetic valves is to imagine the frontal cardiac silhouette vertically bisected along the midline.
The valve that is crossed by the bisection line is the aortic valve. If one then imagines a horizontal bisection such that there are now four quadrants, the pulmonic valve is up and to the patient's left from the aortic, the mitral is down and to the left, and the tricuspid is down and to the right. Consider this interesting film of a patient who has had all four valves replaced.
Which is which? Vertically bisect the heart. This helps to identify the aortic valve, which is also identifiable as the one most in profile. This valve is then the pulmonic, this is the mitral, and this is the tricuspid. On the lateral film, we can then go top to bottom since we've already identified them on the PA.
This method is also not 100% accurate, but combined with the others can give you a reasonable chance at identifying them correctly. I'll end this video with two final examples of some miscellaneous foreign objects. So what is this thing? I know it may look like a person inhaled his or her blackberry, but the wires leading from the device to the head give it away. This is a deep brain stimulator, which can be used to send regular electrical signals to specific regions of the brain most commonly used to treat Parkinson's disease though there are other emerging indications such as refractory depression.
In this case, the implanted pulse generator has been placed into the anterior chest wall, but can also be placed in the abdominal cavity. And last but not least, we have this. It may be obvious that this woman has had bilateral breast implants. However, what can be tricky is when a woman has had a mastectomy, followed by a unilateral implant, who then gets bilateral pneumonia and a poor quality radiograph.
In that situation, it's conceivable for a unilateral implant to be mistaken for a large tumor or infection or perhaps a strange loculated effusion. The final video in this series will review the overall approach to the x-ray including how to go from the individual findings to a cohesive impression, incorporating the clinical context, and I'll also provide some unknown chest x-rays so you can practice incorporation of everything you've learned in this series.