CHEST X-RAYCHEST X-RAY

The plain CXR is the most commonly performed imaging exam because:The plain CXR is the most commonly performed imaging exam because:– Cardio-pulmonary disease is commonCardio-pulmonary disease is common– The exam is quick, easy to do, cheap, with low radiation exposure (a PA CXR gives The exam is quick, easy to do, cheap, with low radiation exposure (a PA CXR gives

only about 3-days-worth of radiation exposure we get anyway from natural sources)only about 3-days-worth of radiation exposure we get anyway from natural sources)– Most importantly the contrast elements involved allow us to see the common Most importantly the contrast elements involved allow us to see the common

pathologies we’re looking forpathologies we’re looking for

It’s all about the contrast: For any imaging exam to be useful, there must It’s all about the contrast: For any imaging exam to be useful, there must be contrast (signal difference) between lesion and surrounding tissuebe contrast (signal difference) between lesion and surrounding tissueThere are 4 tissues that have densities that can be distinguished from each There are 4 tissues that have densities that can be distinguished from each other (have contrast) on plain X-ray:other (have contrast) on plain X-ray:– Calcium (bone)Calcium (bone)– Soft tissue and fluid (not distinguishable on plain X-rays)Soft tissue and fluid (not distinguishable on plain X-rays)– FatFat– Gas/airGas/air

The natural contrast agent of air in the lungs allows us to see the common The natural contrast agent of air in the lungs allows us to see the common soft tissue/fluid pathologies (pneumonia, lung CA, pleural effusion, Kerley soft tissue/fluid pathologies (pneumonia, lung CA, pleural effusion, Kerley lines, etc.)lines, etc.)

The difficulty in reading a CXR is that it’s a 2-D The difficulty in reading a CXR is that it’s a 2-D representation of a 3-D object, with everything representation of a 3-D object, with everything front to back (the z-axis) projected into a single x,y front to back (the z-axis) projected into a single x,y planar imageplanar imageThe task of reading a CXR requires sorting out The task of reading a CXR requires sorting out each important individual piece of anatomy from each important individual piece of anatomy from the overlapped jumblethe overlapped jumbleThis requires a “system” for methodically checking This requires a “system” for methodically checking each of the individual pieces the same way each each of the individual pieces the same way each time so that important findings aren’t missedtime so that important findings aren’t missedAny system is just a crutch to help you remember Any system is just a crutch to help you remember everything you’re supposed to checkeverything you’re supposed to check

Any system that works for you is fineAny system that works for you is fine

Suggested system:Suggested system:– White things (bones, man-made things like White things (bones, man-made things like

tubes, pacer wires, clips)tubes, pacer wires, clips)– Gray things (soft tissues of neck/chest Gray things (soft tissues of neck/chest

wall/under diaphragm, pleural surfaces, wall/under diaphragm, pleural surfaces, mediastinum)mediastinum)

– Black things (lungs, including lung seen Black things (lungs, including lung seen through heart and diaphragm)through heart and diaphragm)

Following image is normal PA CXRFollowing image is normal PA CXRNote that X-ray consists of overlapping areas Note that X-ray consists of overlapping areas of varying opacity which are often separated of varying opacity which are often separated by edge shadows (e.g., edge of heart with by edge shadows (e.g., edge of heart with lung, edge of rib with soft tissue)lung, edge of rib with soft tissue)What creates an edge shadow? Two criteria What creates an edge shadow? Two criteria need to be met:need to be met:– 2 different tissue opacities (calcium, soft 2 different tissue opacities (calcium, soft

tissue/fluid, fat, air) next to each othertissue/fluid, fat, air) next to each other– X-ray beam contacting the interface between the X-ray beam contacting the interface between the

2 opacities tangentially2 opacities tangentially

Following image is normal lateral CXRFollowing image is normal lateral CXRPrinciple of plain X-ray is to try to get at Principle of plain X-ray is to try to get at least 2 projections (to overcome the z-axis least 2 projections (to overcome the z-axis overlap problem)overlap problem)Note that there are 2 hemidiaphragm and Note that there are 2 hemidiaphragm and 2 costophrenic angle edge shadows.2 costophrenic angle edge shadows.Note retrocardiac lucency (the spine Note retrocardiac lucency (the spine should get darker as it is followed down to should get darker as it is followed down to the diaphragm)the diaphragm)

On a lateral CXR what would cause loss of the retrocardiac lucency On a lateral CXR what would cause loss of the retrocardiac lucency and loss of the edge shadow of one hemidiaphragm, and why?and loss of the edge shadow of one hemidiaphragm, and why?There must be violation of one of the 2 criteria that allow you to see There must be violation of one of the 2 criteria that allow you to see the edge shadow in the first place. Because the diaphragm is the edge shadow in the first place. Because the diaphragm is usually dome-shaped, criterion #2 (tangential X-ray) won’t usually usually dome-shaped, criterion #2 (tangential X-ray) won’t usually be violated, so it’s probably that criterion #1 is no longer met (there be violated, so it’s probably that criterion #1 is no longer met (there has been equalization of density at the point where the X-ray is has been equalization of density at the point where the X-ray is tangential to diaphragm)tangential to diaphragm)This could be caused by something of same density as diaphragm This could be caused by something of same density as diaphragm displacing the air-containing lung away from contact with diaphragm displacing the air-containing lung away from contact with diaphragm (pleural effusion)(pleural effusion)Or it could be caused by a process within the lung casing it to Or it could be caused by a process within the lung casing it to become same density as diaphragm (consolidation such as become same density as diaphragm (consolidation such as pneumonia, atelectasis)pneumonia, atelectasis)Vast majority of basilar opacities on CXR are due to pleural effusion, Vast majority of basilar opacities on CXR are due to pleural effusion, consolidation, atelectasis, or a combination of theseconsolidation, atelectasis, or a combination of these

How does one distinguish among pleural How does one distinguish among pleural effusion, consolidation, and atelectasis? (the effusion, consolidation, and atelectasis? (the causes and treatments are different)causes and treatments are different)Classic sign of pleural effusion on CXR is a Classic sign of pleural effusion on CXR is a meniscus (a sharp edge between the fluid meniscus (a sharp edge between the fluid and adjacent lung). In general, a sharp edge and adjacent lung). In general, a sharp edge between the lung and anything suggests that between the lung and anything suggests that a pleural surface is being crossed.a pleural surface is being crossed.Classic sign of atelectasis is evidence of Classic sign of atelectasis is evidence of volume loss (shift of fissures or mediastinum, volume loss (shift of fissures or mediastinum, diaphragm elevation)diaphragm elevation)

Following 2-view CXR shows RML pneumoniaFollowing 2-view CXR shows RML pneumoniaNote opacity that obscures right heart border on Note opacity that obscures right heart border on PA (because RML opacity causes equalization of PA (because RML opacity causes equalization of density at point where X-ray is tangential to right density at point where X-ray is tangential to right heart)heart)On lateral, note sharp inferior edge shadow of the On lateral, note sharp inferior edge shadow of the pneumonia (this is major or oblique fissure pleural pneumonia (this is major or oblique fissure pleural edge with X-ray tangential to 2 different densities)edge with X-ray tangential to 2 different densities)Note hazy, fuzzy superior edge to the pneumonia, Note hazy, fuzzy superior edge to the pneumonia, because it doesn’t involve the whole RML up to because it doesn’t involve the whole RML up to minor (horizontal) fissure. If it had, it would have minor (horizontal) fissure. If it had, it would have had a sharp top edge shadow also.had a sharp top edge shadow also.

Following PA CXR shows left base opacity behind heart Following PA CXR shows left base opacity behind heart (retrocardiac lucency is absent), and expected edge shadows (retrocardiac lucency is absent), and expected edge shadows of left hemidiaphragm, descending aorta, and lower lobe of left hemidiaphragm, descending aorta, and lower lobe pulmonary vessels are all absentpulmonary vessels are all absentOf the big 3 basilar opacity diagnoses, this is atelectasis Of the big 3 basilar opacity diagnoses, this is atelectasis because there are associated signs of volume loss because there are associated signs of volume loss (mediastinum shifted left, left hemidiaphragm elevated)(mediastinum shifted left, left hemidiaphragm elevated)Leftward shift of mediastinum is real and Leftward shift of mediastinum is real and notnot because of because of rotation (spinous processes are midline between medial rotation (spinous processes are midline between medial heads of clavicles)heads of clavicles)This post-operative patient had a mucous plug occluding the This post-operative patient had a mucous plug occluding the left lower lobe bronchus (note the post-op free air under the left lower lobe bronchus (note the post-op free air under the right hemidiaphragm)right hemidiaphragm)

Atelectasis and lung collapse mean the same Atelectasis and lung collapse mean the same thing (airlessness and loss of volume of a piece of thing (airlessness and loss of volume of a piece of lung)lung)Atelectasis (collapse) may involve a subsegment Atelectasis (collapse) may involve a subsegment of lung, a whole lobe, or even a whole lung)of lung, a whole lobe, or even a whole lung)Atelectasis (collapse) is different from Atelectasis (collapse) is different from pneumothorax, an example of which is on the pneumothorax, an example of which is on the following CXRfollowing CXRAlthough lay language may call a pneumothorax a Although lay language may call a pneumothorax a collapsed lung, medically atelectasis (collapse) collapsed lung, medically atelectasis (collapse) does not imply any air in the pleural spacedoes not imply any air in the pleural space

On the following lateral CXR, not the On the following lateral CXR, not the posterior retrocardiac basilar opacity which posterior retrocardiac basilar opacity which obscures one hemidiaphragm edge shadowobscures one hemidiaphragm edge shadowThe obscured hemidiaphragm is the left The obscured hemidiaphragm is the left (identified because of the bowel under it)(identified because of the bowel under it)This is left lower lobe atelectasis (collapse) This is left lower lobe atelectasis (collapse) because of the associated volume loss because of the associated volume loss (elevated left hemidiaphragm)(elevated left hemidiaphragm)This is the lateral CXR that goes with the PA This is the lateral CXR that goes with the PA CXR of LLL collapse already shownCXR of LLL collapse already shown

The 2 following images are a normal 2- The 2 following images are a normal 2- view CXRview CXR

Note the normal basilar/retrocardiac Note the normal basilar/retrocardiac lucency and normal hemidiaphragm edge lucency and normal hemidiaphragm edge shadowsshadows

Following 2-view CXR is of same patient Following 2-view CXR is of same patient who had the preceding normal CXR, but at who had the preceding normal CXR, but at a later timea later time

Note the left base retrocardiac opacity, Note the left base retrocardiac opacity, loss of LLL edge shadows, and volume loss of LLL edge shadows, and volume loss on leftloss on left

This is LLL collapse due to mucous plug in This is LLL collapse due to mucous plug in asthmaticasthmatic

Following 2-view CXR is same asthmatic Following 2-view CXR is same asthmatic patient on a different ED visitpatient on a different ED visit

Note right base retrocardiac opacity, loss Note right base retrocardiac opacity, loss of RLL edge shadows, and volume loss on of RLL edge shadows, and volume loss on rightright

This is RLL collapseThis is RLL collapse

Following CXR shows opacity medially at Following CXR shows opacity medially at apex of right chestapex of right chest

Note sharp lateral edge of the opacity Note sharp lateral edge of the opacity suggesting a pleural surface tangential to suggesting a pleural surface tangential to X-ray, an elevated minor fissureX-ray, an elevated minor fissure

There is associated elevation of right There is associated elevation of right hemidiaphragmhemidiaphragm

This is case of RUL collapseThis is case of RUL collapse

Following 2-view CXR show an opacity Following 2-view CXR show an opacity adjacent to right heart with obscuration of adjacent to right heart with obscuration of right heart borderright heart borderThis is RML collapse because lateral shows This is RML collapse because lateral shows two sharp pleural edge shadows (major and two sharp pleural edge shadows (major and minor fissures) which have moved close to minor fissures) which have moved close to each other as the RML between them has each other as the RML between them has collapsedcollapsedThe wide mediastinum in this case is just due The wide mediastinum in this case is just due to a tortuous aorta in an elderly patientto a tortuous aorta in an elderly patient

Following 2-view CXR shows a left chest Following 2-view CXR shows a left chest opacityopacityLeft heart border is obscured and Left heart border is obscured and retrocardiac lucency is preserved, indicating retrocardiac lucency is preserved, indicating that opacity is anterior in location of LULthat opacity is anterior in location of LULNote sharp edge shadow of left major fissure Note sharp edge shadow of left major fissure on lateralon lateralLeftward shift of mediastinum indicates LUL Leftward shift of mediastinum indicates LUL collapse (due to lung CA, see narrowing of collapse (due to lung CA, see narrowing of trachea and left mainstem bronchus due to trachea and left mainstem bronchus due to adjacent adenopathy)adjacent adenopathy)

Following case shows complete homogeneous Following case shows complete homogeneous opacity of left hemithorax (no, patient did not have opacity of left hemithorax (no, patient did not have a pneumonectomy)a pneumonectomy)Differential diagnosis is between a massive pleural Differential diagnosis is between a massive pleural effusion (so large that it compresses underlying effusion (so large that it compresses underlying lung) and a completely collapsed left lunglung) and a completely collapsed left lungVolume loss on left (mediastinal shift, elevation of Volume loss on left (mediastinal shift, elevation of left hemidiaphragm) indicates complete collapse left hemidiaphragm) indicates complete collapse of left lungof left lungMassive pleural effusion takes up space and Massive pleural effusion takes up space and would shift mediastinum to right.would shift mediastinum to right.

Following CXR shows complete opacity of Following CXR shows complete opacity of the lower 2/3 of right chestthe lower 2/3 of right chest

The opacity forms a sharp edge shadow with The opacity forms a sharp edge shadow with the RUL and extends lateral to the RULthe RUL and extends lateral to the RUL

The sharp edge shadow indicates a pleural The sharp edge shadow indicates a pleural surface, placing the opacity outside lung, in surface, placing the opacity outside lung, in pleural spacepleural space

This is a large pleural effusion, showing what This is a large pleural effusion, showing what is essentially a high meniscus.is essentially a high meniscus.

Following CXR is same patient as preceding, Following CXR is same patient as preceding, but following a thoracentesisbut following a thoracentesisRight effusion is much smaller, but not gone, Right effusion is much smaller, but not gone, and there is now pneumothorax as well, a and there is now pneumothorax as well, a hydropneumthorax (note the air-fluid levels)hydropneumthorax (note the air-fluid levels)In spite of drainage of most of the effusion, In spite of drainage of most of the effusion, there is still nodular thickening of the right there is still nodular thickening of the right pleural surfaces, secondary to tumor implants pleural surfaces, secondary to tumor implants in this patient with malignant mesothelioma, in this patient with malignant mesothelioma, secondary to prior asbestos exposuresecondary to prior asbestos exposure

Another CXR on same patient shows Another CXR on same patient shows progression of mesothelioma encasing progression of mesothelioma encasing

entire right lung (over a year later)entire right lung (over a year later)

Following CXR on 70-year-old female Following CXR on 70-year-old female patient who complains of shortness of patient who complains of shortness of

breath climbing one flight of stairs, breath climbing one flight of stairs, worsening over last couple weeks. Had worsening over last couple weeks. Had

been smoker until 5 years ago when she been smoker until 5 years ago when she had small MIhad small MI

History suggests CHFHistory suggests CHFFindings of CHF on CXR in generalFindings of CHF on CXR in general– Cardiomegaly (width of heart greater than 50% of width of lungs Cardiomegaly (width of heart greater than 50% of width of lungs

at widest point, on standard 6-foot upright PA CXR with good at widest point, on standard 6-foot upright PA CXR with good inspiration and not rotated)inspiration and not rotated)

This is actually assessment of cardiac silhouette, so remember This is actually assessment of cardiac silhouette, so remember possibility of pericardial effusionpossibility of pericardial effusionDon’t apply 50% rule without allowing for any non-standard factorsDon’t apply 50% rule without allowing for any non-standard factors

– Pleural effusionsPleural effusions– Pulmonary vessel enlargement (especially upper lobe vessels Pulmonary vessel enlargement (especially upper lobe vessels

on upright CXR)on upright CXR)– Pulmonary edemaPulmonary edema

Interstitial edema (Kerley lines, peribronchial cuffing, fuzzy vessels)Interstitial edema (Kerley lines, peribronchial cuffing, fuzzy vessels)Alveolar edema (symmetrical air-space infiltrates, diffuse or perihilar/bat Alveolar edema (symmetrical air-space infiltrates, diffuse or perihilar/bat wing)wing)

On this patient’s CXR (standard upright PA), On this patient’s CXR (standard upright PA), cardiac silhouette size is borderline (50%)cardiac silhouette size is borderline (50%)

She has no visible pleural effusionShe has no visible pleural effusion

No visible pulmonary edema (not surprising No visible pulmonary edema (not surprising since she is only symptomatic with exercise)since she is only symptomatic with exercise)

However, she does have upper lobe vessel However, she does have upper lobe vessel enlargement (compare to following CXR enlargement (compare to following CXR which patient had done 2 months before she which patient had done 2 months before she became symptomatic)became symptomatic)

Following image is magnification of upper Following image is magnification of upper lobe vessels when patient was lobe vessels when patient was asymptomaticasymptomatic

Note typically thin upper lobe vessels seen Note typically thin upper lobe vessels seen on upright CXRon upright CXR

Following image is magnification of upper Following image is magnification of upper lobe vessels when patient was lobe vessels when patient was symptomaticsymptomatic

The same upper lobe vessels are now The same upper lobe vessels are now much more dilatedmuch more dilated

Patient has mild CHF, although not Patient has mild CHF, although not pulmonary edemapulmonary edema

Following CXR and 2 magnified views shows patient with Following CXR and 2 magnified views shows patient with CHF and interstitial pulmonary edemaCHF and interstitial pulmonary edemaBe careful about calling a large cardiac silhouette on this AP Be careful about calling a large cardiac silhouette on this AP supine CXR, but allowing for non-standard factors, supine CXR, but allowing for non-standard factors, considering that patient is thin and has taken a very good considering that patient is thin and has taken a very good inspiration, the silhouette is largeinspiration, the silhouette is largeThe images show a good example of Kerley linesThe images show a good example of Kerley lines– Kerley B lines are lines measuring no more than about a cm, Kerley B lines are lines measuring no more than about a cm,

oriented perpendicular to the pleural surface at the edge of the oriented perpendicular to the pleural surface at the edge of the lunglung

– The lines are most visible inferiorly (hydrostatic pressure)The lines are most visible inferiorly (hydrostatic pressure)– Kerley B lines are thickened interlobular septa, separating the Kerley B lines are thickened interlobular septa, separating the

secondary lobules of lung (small ~1cm subunits of lung)secondary lobules of lung (small ~1cm subunits of lung)– The septa are thickened because of edema, and dilatation of The septa are thickened because of edema, and dilatation of

lymphatics and pulmonary venules which run in the septalymphatics and pulmonary venules which run in the septa