How to Read a Chest X-Ray

 

Turn off stray lights, optimize room lighting, view images in order

Patient Data (name history #, age, sex, old films)

Routine Technique: AP/PA, exposure, rotation, supine or erect

Trachea: midline or deviated, caliber, mass

Lungs: abnormal shadowing or lucency

Pulmonary vessels: artery or vein enlargement

Hila: masses, lymphadenopathy

Heart: thorax: heart width > 2:1 ? Cardiac configuration?

Mediastinal contour: width? mass?

Pleura: effusion, thickening, calcification

Bones: lesions or fractures

Soft tissues: don’t miss a mastectomy

ICU Films: identify tubes first and look for pneumothorax

Looking for abnormalities

 

It is best to do a directed search of the chest film rather than simply gazing at the film.  An abnormality will not likely hit you over the head.  Remember that detail vision is only permitted at the fovea centralis of your retina.  This area contains only cones and is the part that you use to read.  The remainder of the retina helps you to put this detailed portion in context and helps to determine whether this is a saber tooth tiger sneaking up on you.  Therefore, it is best to look for abnormalities and to have a planned search in mind.  Your eye gaze should scan all portions of the film, follow lung/mediastinal interfaces and look again carefully in areas where you know that mistakes are easily made, such as over the spine on the lateral view and in the apex on the PA view.

                   

The above diagrams depict the human eye and light waves hitting the fovea, the area of detailed vision.

 

Stare at the 'X' in the center of the image above.  Note how you cannot read the letters in the corner unless you are looking directly at them (ie unless the letter you are trying to read is hitting your retina at

the fovea).

 

 

PA technique for looking at films.  Encompassing the entire lung boundaries (left) , scanning with fovea over each part of lung (right).

 

Lateral scanning technique

Signs

Silhouette sign

One of the most useful signs in chest radiology is the silhouette sign. This was described by Dr. Ben Felson. The silhouette sign is in essence elimination of the silhouette or loss of lung/soft tissue interface caused by a mass or fluid in the normally air filled lung. In other words, if an intrathoracic opacity is in anatomic contact with, for example, the heart border, then the opacity will obscure that border. The sign is commonly applied to the heart, aorta, chest wall, and diaphragm. The location of this abnormality can help to determine the location anatomically.  

Take a moment to review the makeup of the mediastinal margins and the lobes of the lungs that interface with the mediastinum.  Use the back button on your browser to return here.  

For the heart, the silhouette sign can be caused by an opacity in the RML, lingula, anterior segment of the upper lobe, lower aspect of the oblique fissure, anterior mediastinum, and anterior portion of the pleural cavity. This contrasts with an opacity in the posterior pleural cavity, posterior mediastinum, of lower lobes which cause an overlap and not an obliteration of the heart border. Therefore both the presence and absence of this sign is useful in the localization of pathology.

 

 

The right heart border is silhouetted out.  This is caused by a pneumonia, can you determine which lobe the pneumonia affects?  

(click image for answer)

Air Bronchogram

An air bronchogram is a tubular outline of an airway made visible by filling of the surrounding alveoli by fluid or inflammatory exudates. Six causes of air bronchograms are; lung consolidation, pulmonary edema, nonobstructive pulmonary atelectasis, severe interstitial disease, neoplasm, and normal expiration.

 

This patient has bilateral lower lobe pulmonary edema.  The alveoli are filled with fluid making the bronchi visible as an air bronchogram.  The upper right is a closeup of the right side of the film with

arrows outlining a prominent air bronchogram.  The lower right is a CT scan demonstrating an air bronchogram clearly.

 

 

Here is another example of  air bronchograms in both a PA and Lateral film.  Can you spot them?

Solitary Pulmonary Nodule

A solitary nodule in the lung can be totally innocuous or potentially a fatal lung cancer.  After detection the initial step in analyis is to compare the film with prior films if available.  A nodule that is unchanged for two years is almost certainly benign.  If the nodule is completely calcified or has central or stippled calcium it is benign.  Nodules with irregular calcifications or those that are off center should be considered suspicious, and need to be worked up further with a PET scan or biopsy.  

Be sure to evaluate for the presence of multiple nodules as this finding would change the differential entirely.  If the nodule is indeterminate after considering old films and calcification, subsequent steps in the work-up include ordering a CT and a tissue biopsy.  The patient may choose to have an indeterminate nodule removed if there is no evidence of spread on CT as this would diagnose and treat a cancer if present.

 

This patient clearly has a solitary lung nodule present on chest x-ray.  Can you tell which lobe it's in?  Did you spot the other nodule?  Some early lung cancers are missed on the initial chest x-ray because

they are small and faint.  CT may detect these early cancers.

 

PA and Lateral of a subtle right lower lobe cancer.  Can you find it in the frontal projection? (Click on the image for the answer)

Atelectasis

Atelectasis is collapse or incomplete expansion of the lung or part of the lung. This is one of the most common findings on a chest x-ray. It is most often caused by an endobronchial lesion, such as mucus plug or tumor. It can also be caused by extrinsic compression centrally by a mass such as lymph nodes or peripheral compression by pleural effusion. An unusual type of atelectasis is cicatricial and is secondary to scarring, TB, or status post radiation.

Atelectasis is almost always associated with a linear increased density on chest x-ray. The apex tends to be at the hilum. The density is associated with volume loss. Some indirect signs of volume loss include vascular crowding or fissural, tracheal, or mediastinal shift, towards the collapse. There may be compensatory hyperinflation of adjacent lobes, or hilar elevation (upper lobe collapse) or depression (lower lobe collapse). Segmental and subsegmental collapse may show linear, curvilinear, wedge shaped opacities. This is most often associated with post-op patients and those with massive hepatosplenomegaly or ascites .

 

Note the loss of the right heart border silhouette due to partial atelectasis of the RML.  Atelectasis is usually, but not always, a benign finding as in this example which was caused by an endobronchial

mass in the RML.

 

This is a PA and lateral film showing round atelectasis, where the lung becomes attached to the chest wall by an area of previous inflammation.  The lung then rolls up, causing this opacity.

Left Lung Atelectasis

Left Upper Lobe

The left lung lacks a middle lobe and therefore a minor fissure, so left upper lobe atelectasis presents a different picture from that of the right upper lobe collapse. The result is predominantly anterior shift of the upper lobe in left upper lobe collapse, with loss of the left upper cardiac border. The expanded lower lobe will migrate to a location both superior and posterior to the upper lobe in order to occupy the vacated space. As the lower lobe expands, the lower lobe artery shifts superiorly. The left mainstem bronchus also rotates to a nearly horizontal position.

This patient suffered from left upper lobe atelectasis following right upper lobectomy.

 

PA and Lateral of a patient with Left Upper Lobe Collapse (arrows).  This characteristic finding on CXR is known as the Luftsichel Sign and may represent collapse due to obstruction from a bronchogenic

carcinoma.  The lucency between the mediastinum and the collapsed LUL is caused by hyperexpansion of the superior segment of the LLL.

 

Left Lower Lobe

Atelectasis of either the right or left lower lobe presents a similar appearance. Silhouetting of the corresponding hemidiaphragm, crowding of vessels, and air bronchograms are sometimes seen, and silhouetting of descending aorta is seen on the left. It is important to remember that these findings are all nonspecific, often occuring in cases of consolidation, as well. A substantially collapsed lower lobe will usually show as a triangular opacity situated posteromedially against the mediastinum.

 

These radiographs demonstrate left lower lobe atelectasis followed by partial resolution, respectively.

 

Another PA film of LLL atelectasis (arrows).  Note the elevation of the left hemidiaphragm.

Right Lung Atelectasis

Right Upper Lobe

Right upper lobe atelectasis is easily detected as the lobe migrates superomedially toward the apex and mediastinum. The minor fissure elevates and the inferior border of the collapsed lobe is a well demarcated curvilinear border arcing from the hilum towards the apex with inferior concavity. Due to reactive hyperaeration of the lower lobe, the lower lobe artery will often be displaced superiorly on a frontal view.

 

Note the elevation of the horizontal fissure (arrows) caused by RUL atelectasis.

 

Right Middle Lobe

Right middle lobe atelectasis may cause minimal changes on the frontal chest film. A loss of definition of the right heart border is the key finding. Right middle lobe collapse is usually more easily seen in the lateral view.  The horizontal and lower portion of the major fissures start to approximate with increasing opacity leading to a wedge of opacity pointing to the hilum.  Like other cases of atelectasis, this collapse may by confused with right middle lobe pneumonia.

Right middle lobe atelectasis can be difficult to detect in the AP film. The right heart border is indistinct on the AP film. The lateral, though, shows a marked decrease in the distance between the horizontal

and oblique fissures.

 

Right Lower Lobe

Silhouetting of the right hemidiaphragm and a triangular density posteromedially are common signs of right lower lobe atelectasis. Right lower lobe atelectasis can be distinguished from right middle lobe atelectasis by the persistance of the right heart border.

Notice the stretched vessels in the hyperexpanded right upper lobe in right lower lobe atelectasis. The right hilum is also displaced inferiorly. This is a tough one.

Pulmonary Edema

There are two basic types of pulmonary edema.  One is cardogenic edema caused by increased hydrostatic pulmonary capillary pressure.  The other is termed noncardogenic pulmonary edema, and is caused by either altered capillary membrane permeability or decreased plasma oncotic pressure.  

A helpful mnemonic for noncardiogenic pulmonary edema is NOT CARDIAC (near-drowning, oxygen therapy, transfusion or trauma, CNS disorder, ARDS, aspiration, or altitude sickness, renal disorder or resuscitation, drugs, inhaled toxins, allergic alveolitis, contrast or contusion.  

On a CXR, cardiogenic pulmonary edema can show; cephalization of the pulmonary vessels, Kerley B lines or septal lines, peribronchial cuffing, "bat wing" pattern, patchy shadowing with air bronchograms, and increased cardiac size.  Unilateral, miliary and lobar or lower zone edema are considered atypical patterns of cardiac pulmonary edema.  A unilateral pattern may be caused by lying preferentially on one side.  Unusual patterns of edema may be found in patients with COPD who have predominant upper lobe emphysema.

 

PA film of a patient with pulmonary edema showing cephalization of pulmonary veins and indistinctness of the vascular margins.  The heart is enlarged.

 

Would you favor pneumonia or CHF in this patient? Why? What pattern is shown?(Click image for answer)

 

 

Above are two films from the same patient.  The left film clearly shows diffuse pulmonary edema with loss of both hemidiaphragms and silouhetting of the heart.  The film on the right was taken two days

later after partial resolution of the edema.

Congestive Heart Failure

Congestive heart failure (CHF) is one of the most common abnormalities evaluated by CXR. CHF occurs when the heart fails to maintain adequate forward flow. CHF may progress to pulmonary venous hypertension and pulmonary edema with leakage of fluid into the interstitium, alveoli and pleural space.

The earliest CXR finding of CHF is cardiomegaly, detected as an increased cardiothoracic ratio (>50%). In the pulmonary vasculature of the normal chest, the lower zone pulmonary veins are larger than the upper zone veins due to gravity. In a patient with CHF, the pulmonary capillary wedge pressure rises to the 12-18 mmHg range and the upper zone veins dilate and are equal in size or larger, termed cephalization. With increasing PCWP, (18-24 mm. Hg.), interstitial edema occurs with the appearance of Kerley lines.  Increased PCWP above this level is alveolar edema, often in a classic perihilar bat wing pattern of density. Pleural effusions also often occur.

CXR is important in evaluating patients with CHF for development of pulmonary edema and evaluating response to therapy as well.

 

This is a typical chest x-ray of a patient in severe CHF.  Note the cardiomegaly, alveolar edema, and haziness of vascular margins.

 

The left image demonstrates a patient with a severe pulmonary edema as a result of CHF.  The right image is the same patient after significant resolution.

Kerley B lines

These are horizontal lines less than 2cm long, commonly found in the lower zone periphery.  These lines are the thickened, edematous interlobular septa.  Causes of Kerley B lines include; pulmonary edema, lymphangitis carcinomatosa and malignant lymphoma, viral and mycoplasmal pneumonia, interstital pulmonary fibrosis, pneumoconiosis, sarcoidosis.  They can be an evanescent sign on the CXR of a patient in and out of heart failure.

 

The patient above is suffering from congestive heart failure resulting in interstitial edema.   Notice the Kerley's B lines in right periphery (arrows).

Near drowning

The CXR may be normal, especially in children, if laryngospasm (diving reflex) occurs. Otherwise, a "batwing" pattern of pulmonary edema is seen. The situation may be complicated by ARDS.

 

PA of near drowning patient after resuscitation

Pneumonia

Pneumonia is airspace disease and consolidation.  The air spaces are filled with bacteria or other microorganisms and pus. Other causes of airspace filling not distinguishable radiographically would be fluid (inflammatory), cells (cancer), protein (alveolar proteinosis) and blood (pulmonary hemorrhage), Pneumonia is NOT associated with volume loss.  Pneumonia is caused by bacteria, viruses, mycoplasmae and fungi.

The x-ray findings of pneumonia are airspace opacity, lobar consolidation, or interstitial opacities. There is usually considerable overlap. Again, pneumonias is a space occupying lesion without volume loss. What differentiates it from a mass? Masses are generally more well-defined. Pneumonia may have an associated parapneumonic effusion.

The type of pneumonia is sometimes characteristic on chest x-ray:

Lobar - classically Pneumococcal pneumonia, entire lobe consolidated and air bronchograms common

Lobular - often Staphlococcus, multifocal, patchy, sometimes without air bronchograms

Interstitial - Viral or Mycoplasma; latter starts perihilar and can become confluent and/or patchy as disease progresses, no air bronchograms

Aspiration pneumonia - follows gravitational flow of aspirated contents; impaired consciousness, post anesthesia, common in alcoholics, debilitated, demented pts; anaerobic (Bacteroides and Fusobacterium)

Diffuse pulmonary infections - community acquired (Mycoplasma, resolves spontaneoulsy) nosocomial (Pseudomonas, debilitated, mechanical vent pts, high mortality rate, patchy opacities, cavitation, ill-defined nodular) immunocompromised host(bacterial, fungal, PCP)

 

Major differentiating factors between atelectasis and pneumonia

Atelectasis    Pneumonia   

Volume Loss

Associated Ipsilateral Shift 

Linear, Wedge-Shaped

Apex at Hilum

 

Normal or Increased Volume

No Shift, or if Present Then Contralateral

Consolidation, Air Space Process

Not Centered at Hilum

 

 

Air bronchograms can occur in both.

 

                                                          

 

These are  PA and lateral films of RML pneumonia (arrows). Note the indistinct borders, air bronchograms, and silhouetting of the right heart border.

 

 

PA and Lateral films of RUL pneumonia

Tuberculosis

Primary tuberculosis (TB) is the initial infection with Mycobacterium tuberculosis.  Post-primary TB is reactivation of a primary focus, or continuation of the initial infection. Radiographically, TB is represented by consolidation, adenopathy, and pleural effusion. A Ghon focus is an area of consolidation that most commonly occurs in the mid and lower lung zones.  A Ghon complex is the addition of hilar adenopathy to a Ghon focus.

Radiographic features of post-primary TB are; focal patchy airspace disease "cotton wool" shadows, cavitation, fibrosis, nodal calcification, and flecks of caseous material. These occur most commonly in the posterior segments of the upper lobes, and superior segments of the lower lobes.

Endobronchial TB involves the wall of a major bronchus. Complications of endobronchial TB are cicatrical stenosis and obstruction.

 

This is a PA film of a patient who has had tuberculosis for years.  This shows fibrosis, cavitation, and calcification, particularly in the left upper lobe.

Pulmonary Hemorrhage

Pulmonary hemorrhage has an appearance like that of other airspace filling processes (pneumonia, edema) which have opacity often with air bronchograms.  It is caused by trauma, Goodpastrue's syndrome, bleeding disorders, high altitude, and mitral stenosis.  Blood fills the bronchi and eventually the alveoli.  Pulmonary hemorrhage is notable in that it may clear more quickly than other alveolar densities such as pneumonia.

 

PA and Lateral films of a patient with right upper lobe hemorrhage.  Notice the large pleural effusion in the left hemithorax.

Pulmonary Embolism

Pulmonary embolism (PE) is not uncommon in the inpatient setting.  The primary source is thrombus from the deep veins of the legs.  Roughly ten percent of pulmonary embolisms result in pulmonary infarction, but many patients die of PE without being diagnosed.  The primary purpose of a chest film in suspected PE is to rule out other diagnoses as a cause of dyspnea or hypoxia.  Most CXRs in patients with a PE are normal.  Signs that may be present in PE are; Westermark's sign (oligemia in area of involvement), increased size of a hilum (caused by thrombus impaction), atelectasis with elevation of hemidiaphragm and linear or disk shaped densities, pleural effusion, consolidation, and Hampton's hump (rounded opacity).  In the case of pulmonary infarctions, the main radiographic feature is multifocal consolidation at the pleural base in the lower lungs.  Several other important modalities are used when investigating possible PE.  These modalities are venous ultrasound, V/Q scan, pulmonary arteriogram, and CT angiogram (CTA).  Remember, if the CXR of a patient with hypoxia is normal you should consider PE.

The workup of suspected PE can be divided into two populations.  In the inpatient setting a CTPA will likely be more definitive than a V/Q scan, as it may disclose other causes of hypoxia not shown on CXR.  If the patient has leg swelling, a venous ultrasound of the leg veins should be done to exclude DVT.  In the outpatient setting a V/Q scan should be the first test and will less likely be indeterminate than in the inpatient setting.  There is also a lower radiation dose for V/Q scans than for CTPA.  If

these studies are inconclusive a pulmonary arteriogram is the definitive, but more invasive test.

 

These are two PA fiilms demonstrating Hampton's hump (rounded opacities) in patients with pulmonary embolism.

What is the most common chest x-ray finding in PE? (Click for answer)

 

Above are 2 CT scans from the same patient demonstrating a large pulmonary embolus.Which vessel is it affecting? (Click for answer and arrows)

Pleural Effusion

Common causes for a pleural effusion are CHF,  infection (parapneumonic), trauma, PE, tumor, autoimmune disease, and renal failure.

On an upright film, an effusion will cause blunting on the lateral and if large enough, the posterior costophrenic sulci. Sometimes a depression of the involved diaphragm will occur. A large effusion can lead to a mediastinal shift away from the effusion and opacify the hemothorax. Approximately 200 ml of fluid are needed to detect an effusion in the frontal film vs. approximately 75ml for the lateral. Larger effusions, especially if unilateral, are more likely to be caused by malignancy than smaller ones.

In the supine film, an effusion will appear as a graded haze that is denser at the base.  The vascular shadows can usually be seen through the effusion.  An effusion in the supine view can veil the lung tissue, thicken fissure lines, and if large, cause a fluid cap over the apex.  There may be no apparent blunting of the lateral costophrenic sulci.

A lateral decubitis film is helpful in confirming an effusion in a bedridden patient as the fluid will layer out on the affected side (unless the fluid is loculated). Today,

ultrasound is also a key component in the diagnosis.  Ultrasound is also used to guide diagnostic aspiration of small effusions.

 

PA and lateral film of a patient with bilateral pleural effusions.  Note the concave menisci blunting both posterior costophrenic angles.

 

The CT above on the left demonstrates a large infected pleural fluid collection, an empyema.  Compare and contrast that to the image on the right which is an intrapulmonary abscess.

Mastectomy

One must carefully examine the soft tissues.  The patient below has had a mastectomy.  The hemithoraces are asymmetric in density.  The finding of a mastectomy should also make you look even closer at the bones and lungs for metastases.

 

PA and Lateral films of a patient post left mastectomy

This case shows the importance of examining the soft tissues carefully.  At first, it may appear that the asymmetry in density between the two hemithoraces is caused by a left pleural effusion, giving the appearance of a graded density.  A closer look reveals that the asymmetry is due to the removal of the left breast.

Pneumothorax

A pneumothorax is defined as air inside the thoracic cavity but outside the lung.   A spontaneous pneumothorax (PTX) is one that occurs without an obvious inciting incident. Some causes of spontaneous PTX are; idiopathic, asthma, COPD, pulmonary infection, neoplasm, Marfan's syndrome, and smoking cocaine.  However, most pneumothoraces are iatrogenic and caused by a physician during surgery or central line placement.  Trauma, such as a motor vehicle accident is another important cause.  A tension PTX is a type of PTX in which air enters the pleural cavity and is trapped during expiration usually by some type of ball valve-like mechanism.  This leads to a buildup of air increasing intrathoracic pressure.  Eventually the pressure buildup is large enough to collapse the lung and shift the mediastinum away from the tension PTX.  If it continues, it can compromise venous filling of the heart and even death.

On CXR, a PTX appears as air without lung markings in the least dependant part of the chest.  Generally, the air is found peripheral to the white line of the pleura.  In an upright film this is most likely seen in the apices.  A PTX is best demonstrated by an expiration film.  It can be difficult to see when the patient is in a supine position.  In this position, air rises to the medial aspect of the lung and may be seen as a lucency

along the mediastinum.  It may also collect in the inferior sulci causing a deep sulcus sign.

A hydropneumothorax is both air and fluid in the pleural space. It is characterized by an air-fluid level on an upright or decubitus film in a patient with a pneumothorax. Some causes of a hydropneumothorax are trauma, thoracentesis, surgery, ruptured esophagus, and empyema.

This image shows a close-up of a pneumothorax in an upright PA film as a white pleural line (red arrow) with atmospheric air outside of it.  No pulmonary vascular markings are seen outside of the line.  Notice

the predilection to the apices and the periphery.

 

The above film shows a right sided tension pneumothorax with right sided lucency and leftward mediastinal shift.  This is a medical emergency.  Failure to place a right chest tube immediately could

allow venous return to diminish and lead to possible death.

 

Left is a supine view of a PTX, note the medial position of the air.  Right is an image demonstrating the deep sulcus sign (letter D in the image) in supine views of a PTX.

 

The above three images show a hydropneumothorax in three different views.  The PA, lateral, and right decube reveal a layering out of the air and fluid.  

The right decube film demonstrates a right hydropneumothorax. Note the pleural air/fluid level demonstrated by the horizontal air/fluid interface (arrows).

Interstitial Pulmonary Fibrosis

Interstitial pulmonary fibrosis has many causes.  The six most common causes of diffuse interstitial pulmonary fibrosis are idiopathic (IPF, >50% of cases), collagen vascular disease, cytotoxic agents and nitrofurantoin, pneumoconioses, radiation, and sarcoidosis.  Clinically the patient with IPF will present with progressive exertional dyspnea and a nonproductive cough.  Radiographically, IPF is associated with hazy "ground glass" opacification early and volume loss with linear opacities bilaterally, and honeycomb lung in the late stages.  IPF carries a poor prognosis with death due to pulmonary failure usually occurring within 3-6 years of the diagnosis unless lung transplant is performed. 

 

Interstitial Pulmonary Fibrosis

Emphysema

Emphysema is loss of elastic recoil of the lung with destruction of pulmonary capillary bed and alveolar septa.  It is caused most often by cigarette smoking and less commonly by alpha-1 antitrypsin deficiency.  Functional hallmarks are decreased airflow (decreased FEV1) and diffusing capacity (decreased DLCO2).

Emphysema is commonly seen on CXR as diffuse hyperinflation with flattening of diaphragms, increased retrosternal space, bullae (lucent, air-containing spaces that have no vessels that are not perfused)  and enlargement of PA/RV (secondary to

chronic hypoxia) an entity also known as cor pulmonale. Hyperinflation and bullae are the best radiographic predictors of emphysema. However, the radiographic findings correlate poorly with the patientâs pulmonary function tests. CT and HRCT (high resolution CT) has emerged as a technique to evaluate different types, panlobular, intralobular, paraseptal and for guidance prior to volume reduction surgery.

Occasionally the trachea is very narrow in the mediolateral plane in emphysema.  "Saber sheath" tracheal deformity is when the coronal diameter is less than 2/3 that of the sagittal.

In smokers with known emphysema the upper lung zones are commonly more involved than the lower lobes. This situation is reversed in patients with alpha-1 anti-trypsin deficiency, where the lower lobes are affected.

Chronic bronchitis commonly occurs in patients with emphysema and is associated with bronchial wall thickening.

 

Note bilateral flattening of the diaphragms and significant hyperinflation as demonstrated by visualization of 11 posterior ribs.

Trauma - Rib fracture

Rib fractures have the appearance of an abrupt discontinuity in the smooth outline of the rib.  A lucent fracture line may be seen.  A rib fracture may not be visible on a CXR.  CXR is taken to assess for pneumothorax, but it may show them.  If it is necessary to exclude a rib fracture, oblique rib detail films should be obtained.

A common pattern for evaluating the ribs is to examine the posterior portions of the ribs first, then the anterior portions, and finish be examining the lateral aspects of each rib.  If you see an abnormality, follow that rib in its entirety. 

Fracture of the upper three ribs is associated with an increased risk of aortic injury because of the excessive force needed to fracture these ribs.  Fracture of the lower three ribs can be associated with liver or spleen injury.  Multiple bilateral rib fractures in various stages of healing are associated with child abuse in children or alcohol abuse.

 

PA and Lateral films of right ninth rib fracture.  No PTX was present. 

 

CT from the same patient in the PA and lateral films above.  This clearly shows the rib displacement near the liver on the right.

 

This PA film shows a left flail chest, or multiple rib fractures, that can now move paradoxically with the rest of the thoracic cage.

Anterior Mediastinal Mass

Anterior mediastinal masses consist of the 4 "T's" (Terrible lymphadenopathy, Thymic tumors, Teratoma, Thyroid mass) and aortic aneurysm, pericardial cyst, epicardial fat pad.  Usually CT or fine needle aspiration is needed to make the definitive diagnosis of  an anterior mediastinal mass. 

 

T-cell Lymphoma

 

 

Note in these images that the hilum can be seen through the mass.  It is not a hilar mass.  The lateral shows nothing abnormal posteriorly.

 

The CT sections demonstrate the mass in the anterior mediastinum (arrows) at the aortopulmonary window which was a thymoma.

Middle Mediastinal Mass

The most common cause of a middle mediastinal mass is lymphadenopathy due to metastases or primary tumor.  Other causes include hiatial hernia, aortic aneurysm, thyroid mass, duplication cyst, and bronchogenic cyst.  

 

Can you spot the abnormality? (Click each of the images for arrows)This mass above the aortic arch can be seen to be posterior to the aorta on the lateral.  It does not

silhouette out the superior margin of the aorta. A chest CT was performed to further evaluate the mass.

 

This CT scan shows that the mass is posterior to the aorta, smoothly marginated, low density, and associated with the esophagus.  It is an esophageal duplication cyst.

 

 

Above is a PA, lateral, and aortogram of a saccular aortic aneurysm, another cause of a middle mediastinal mass.

Posterior Mediastinal Mass

The differential for a posterior mediastinal mass includes; neoplasm, lymphadenopathy, aortic aneurysm, adjacent pleural or lung mass, neurenteric cyst or lateral meningocele, and extramedullary hematopoiesis.

 

Note that this mass is detected by a pleural margin search as you move your eye along the superomedial part of the right lung.  The interface is interrupted. Think about the anatomy of the lung in this area. The anterior mediastinum ends at the level of the clavicles. Any abnormality in the apex of the

thorax must be posterior in the chest.  

 

The mass projects above the clavicles, therefore it is not an anterior structure.

 

 

This MRI shows the mass is extrapleural and associated with the spinal nerves.  It is a schwannoma, a benign tumor of the nerve sheath.

Pleural and Extra-pleural Masses

The differential for pleural mass includes; metastases (especially adenocarcinoma and malignant thymoma), loculated pleural effusions (pseudotumor), malignant mesothelioma, pleural plaques from asbestosis (bilateral densities), and lymphoma.  The differential for extrapleural mass includes rib tumor, rib infection (including chest wall fungal infection), neurofibroma or schwannoma (may erode a rib, but does not destroy it), and lipoma.  One must first determine whether a mass arises from inside the lung or outside, an oblique margin with lung tissue indicates that the process is pleural or extrapleural.  Distinguishing between a pleural and extrapleural mass can be challenging.  If the center of the lesion is inside the chest wall, a pleural process is likely.  Rib destruction indicates extrapleural involvement and possibly the origin of the mass.

 

Lateral film of an intraparenchymal mass.  Note acute margins like "A" in the diagram on the right. Both "B" and "C" have oblique margins. "B" demonstrates a pleural mass while "C" is an extrapleural chest

wall mass.

Pericardial Effusion

Pericardial effusion causes an enlarged heart shadow that is often globular shaped (transverse diameter is disproportionately increased).  A "fat pad" sign, a soft tissue stripe wider than 2mm between the epicardial fat and the anterior mediastinal fat can be seen anterior to the heart on a lateral view. Serial films can be helpful in the diagnosis especially if rapid changes in the size of the heart shadow are observed. Approximately 400-500 ml of fluid must be in the pericardium to lead to a detectable change in the size of the heart shadow on PA CXR. Pericardial effusion can be definitively diagnosed with either echocardiography or CT.  It can be critical to diagnose pericardial effusion because if it is acute it may lead to cardiac tamponade, and poor cardiac filling.  In the postoperative patient it could be a sign of bleeding, necessitating a return to the OR.

PA of a patient with a pericardial effusion.

 

 

A lateral film and closeup of a pericardial effusion showing the anterior mediastinal fat (blue arrows) and epicardial fat (red arrows) separated by a soft tissue stripe reflecting the pericardial effusion seen

edge-on.

Pneumomediastinum

Findings for pneumomediastinum include; streaky lucencies over the mediastinum that extend into the neck,  and elevation of the parietal pleura along the mediastinal borders.

Causes of pneumomediastinum include; asthma, surgery (post-op complication), traumatic tracheobronchial rupture, abrupt changes in intrathoracic pressure (vomiting, coughing, exercise, parturition), ruptured esophagus, barotrauma, and smoking crack cocaine.

Pneumomediastinum should be distinguished from pneumopericardium and pneumothorax. In pneumopericardium, air can be present underneath the heart, but does not enter the neck.

 

PA film of a pneumomediastinum.

 

CT scans clearly demonstrating the presence of air in the mediastinum (red arrows) and subcutaneous emphysema (yellow arrows).

Diaphragmatic hernia

There are 3 types of diaphragmatic hernia that may be seen in CXR.  By far the most common is a hiatal hernia - the stomach slips through the esophageal hiatus into the chest.  A Bochdalek hernia is through a weakness in the diaphragm, and usually occurs on the left side posteriorly (Bochdalek - back and to the left).  Morgagni hernias typically occur medially.  Weakness of the diaphragm can occur without frank herniation of abdominal contents.  This is termed an eventration, and it usually occurs on the right with a portion of the liver bulging cephalad.

 

PA and lateral of hiatal hernia. Can you see the air-filled "mass" posterior to the heart?

Hilar Adenopathy

Enlargement of the lymph nodes within the lung hilum can be an important finding for underlying pathology.

A differential of possible etiologies can be broken up into three different categories:

Inflammation (sarcoidosis, silicosis) Neoplasm (lymphoma, metastases, bronchogenic carcinoma)

Infection (tuberculosis, histoplasmosis, infectious mononucleosis)

An important consideration to keep in mind is that since the pulmonary arteries also course through the same area, enlargement of these vessels may be confused with hilar adenopathy.  Typically, lymphadenopathy has a more lumpy-bumpy appearance, while an enlarged pulmonary artery appears smooth.

One of the following pictures displays hilar adenopathy and the other shows pulmonary artery enlargement. Can you determine which one is which?

The above left picture shows bilateral pulmonary artery enlargement.  Note the smooth contours of the arteries.  The above right picture shows the lumpy-bumpy opacities characteristic of hilar adenopathy.

Solitary Pulmonary Nodule

A solitary pulmonary nodule is not an uncommon finding on a chest x-ray.   A solitary pulmonary nodule can result from a wide range of causes.   Most nodules are benign but some can be malignant.

Nodules are diagnosed as benign if they:

Show little or no growth for 2 years Calcification

o Central, laminated or diffuse pattern indicates a granuloma

o Eccentric calcification can be seen in a carcinoma or in a cancer that has engulfed a granuloma

 

The CT image above shows a right lower lobe centrally calcified nodule, consistent with a benign granuloma.

 

A differential of possible etiologies is as follows:

Granuloma – usually caused by fungal infections like histoplasmosis or tuberculosis

Lung Carcinoma

Solitary metastasis – usually from colon, breast, kidney, ovary, or testis

Round pneumonia

Abscess

Round atelectasis

Hamartoma – popcorn calcification is sometimes seen

Sequestration

Arteriovenous malformation

Granulomas and lung cancer are by far the two most common causes for a pulmonary nodule.

Other things can cause an apparent nodule but are actually outside the lung including:

Fluid in an interlobar fissure Pleural plaques – small, often calcified, plate-like surfaces on the pleura often

caused by asbestos fibers that invade the pleura from the lungs

Skin lesions – nipple shadow, mole, lipoma, etc.

Incidental small pulmonary nodules, especially less than 5 mm, are an extremely common finding on chest CT in the population over age 50.  The current recommended follow-up of incidental pulmonary nodules per the Fleischner Society 2005 is given below.  In a patient with a prior history of malignancy, a difference in intervals can be based on additional considerations of the likelihood of pulmonary metastases given the specific primary.

Low Risk Patient

≤ 4mm No follow-up needed

4-6mm 12 mo; if no change - stop

6-8mm 6-12 mo; no change - follow-up at 18-24 mo

> 8mm CT follow-up at 3, 9, 24mo or PET/CT, or biopsy

High Risk Patient (eg. smoking history or history of malignancy)

≤ 4mm 12 mo; if no change - stop

4-6mm 6-12mo; no change - follow-up at 18-24 mo

6-8mm 3-6mo; no change - follow-up at 18-24 mo

> 8mm CT follow-up at 3, 9, 24mo or PET/CT, or biopsy

Lung Cancer

The cell type of primary malignancies of the lung can often be distinguished by their pattern of growth, appearance and location.  Across the world, lung cancer causes to more cancer deaths than any other tumor.

The most common staging system used for non-small cell lung cancer is the TNM staging as follows:

 

The best chance for cure is resection of the tumor.  However, it has been found that not all patients with lung cancer will benefit from surgery.  These tumors are thereby unresectable as below.  Other patients may be “unresectable” due to comorbidities such as emphysema or cardiac disease.

Lung cancers are unresectable once they have progressed to a TNM staging of any of the below.

T4 – Invasion of the mediastinum or involvement of the heart, great vessels, trachea, esophagus, vertebral body, or carina; or neoplasia associated with a malignant pleural or pericardial effusion, or satellite nodules in the same lobe

N3 – Metastasis to contralateral mediastinal and hilar nodes, ipsilateral or contralateral scalene or supraclavicular nodes

M1 – distant metastasis present

T4 or N3 would stage the tumor IIIB, M1 would stage it Stage IV.

The above CT image shows the spiculated appearance of a lung cancer.

 

The six cell types of primary lung carcinomas with their typical appearances are as follows:

Adenocarcinoma – (35-50%) Peripheral, sometimes associated with scars, high incidence of early metastasis

Squamous Cell Carcinoma – (30%) Central, with hilar involvement, cavitation is common, slow growing

Small Cell - (15-20%) Central, cavitation is rare, hilar and mediastinal masses often the dominant feature, rapid growth and early metastases

Large cell – (10-15%) Peripheral, large, cavitation present

Bronchaveolar – (3%) Peripheral, rounded appearance, pneumonia-like infiltrate (air bronchograms), occasionally multifocal

Carcinoid – (less than 1%) Typically a well defined endobronchial lesion; nodal, liver and brain metastases may enhance densely (i.e. They may be hypervascular)

The above image shows a right lower lobe squamous cell cancer.  Notice the cavitation, which is found more characteristically in squamous cell than in other bronchogenic carcinomas.