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Chest X-ray interpretation NOT JUST By William Pezzotti, MSN, RN, ACNP-BC, CEN BLACK AND WHITE

CHEST X-RAYS (CXRs) are one of the oldest noninvasive methods for iden- tifying abnormalities in the chest. Even though healthcare providers prescribe CXRs and interpret the results, nurses are often the first to read the radio- logist’s report and provide the interpretation to the attending physician or a designate.1 In many hospital systems across the United States, nurses who work in the ICU or ED routinely implement specific standing orders, including obtaining a CXR for an unexpected issue such as chest pain, respiratory distress, unexplained hypoxemia, or unequal breath sounds.1 This article reviews how to recognize basic normal anatomy and life-threatening abnormalities on a CXR.

Understanding CXRs X-rays are short wavelengths of electromagnetic radiation that penetrate mat- ter.2 They’re basically photographs, but instead of light they use radiation to provide contrast. The amount of radiation that X-rays produce is very small (0.2 millisieverts, or mSv; this unit belongs to the same family as the liter and kilogram) and cause only 0.00001% of fatal cancers in the United States.3,4 Evaluating a CXR is a skill that requires careful observation and a good understanding of chest anatomy.4 (See Structures of the lung.) The technique used to obtain the CXR determines its overall quality. Two of the most common views used in the acute care setting are postero- anterior (PA) and anteroposterior (AP), or frontal views of the chest.2 For PA

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Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. views, the X-ray beam passes CXRs should always be taken dur- metal), water (soft tissue), fat, and through the chest from the back to ing maximum inspiration to allow gas (air).2,7 the front. The patient must stand visualization of any pulmonary ab- • Bone/metal density appears all while this CXR is taken. In AP views, normalities.5 When the patient in- white, or completely radiopaque, the beam passes through the chest spires deeply, the diaphragm should as do bullets, coins, ECG electrodes, from the front to the back. be seen at the segment of the 6th rib and pacemakers.5,8 Portable CXRs should generally anteriorly.6 If 10 posterior ribs can be • Water (soft tissue) density looks be reserved for acutely ill patients counted above the diaphragm, it’s an white to gray on the CXR. The heart, and others who can’t stand.2 Portable excellent inspiratory CXR. If fewer liver, diaphragm, spleen, and blood CXRs performed at the patient’s bed- than 10 ribs can be counted above vessels will also cause this appear- side are AP views.2,4 A major disad- the diaphragm, it’s either poor inspi- ance. This is largely because the or- vantage of an AP view is that the ratory effort or a sign of low lung gans are the same density as water.8 structures in the anterior part of the volume.2 The right hemidiaphragm In erect CXRs, fluid can often be chest, including the heart, look big- is usually higher than the left be- seen collecting at the lung bases and ger because of magnification. This cause of the location of the liver. appear as dense opacities blocking could lead to an incorrect diagnosis Poor inspiratory effort can cause the adjacent structures in the chest cav- of cardiomegaly.4 CXR to appear whiter, with increased ity.5 This is the most common loca- A lateral view may reveal lesions lung markings, and can also give a tion of pleural effusions on a CXR. behind the heart, near the mediasti- false impression that a lower lobe • Fat appears gray. This tissue is less num, or near the diaphragm. The pneumonia is present.3 dense than bone/metal but more frontal and lateral views provide a dense than air and is most often seen three-dimensional view of the chest Penetrating issues in CXRs involving the breasts and fat and let the clinician localize infil- X-rays distinguish objects based pads. trates or other lesions that might on relative densities. The four basic • Gas (air) density is black, or ra- otherwise be difficult to find.2 densities on a CXR are bone (or diolucent, and is seen on review of

Structures of the lung

The main lung structures as seen in an anterior view; the carina is at the bifurcation of the right and left mainstem bronchi.

Right main bronchus Left mainstem bronchus Right superior lobe bronchus Left pulmonary Superior lobe artery

Left pulmonary Middle lobe veins Right middle lobe bronchus

Right inferior lobe bronchus

Inferior lobe

Right Left

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Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. the lungs, trachea, bronchi, and al- the middle lobe of veoli.5 Air tends to rise to the highest the right lung.8 Pos- Visualizing the diaphragm point in the chest cavity, so a pneu- terior structures are The right hemidiaphragm should be higher than the left mothorax is most commonly seen at the descending aor- by about 3 cm because of the liver. The outline of the the lung apices when the patient is ta, hemidiaphragms, diaphragm should be smooth. erect.5 and both lower lung The penetration of a CXR is af- lobes.8 fected by the duration of exposure Review all aspects and the power of the beam. A poorly of the CXR by using penetrated CXR looks light and soft the ABCDEF ap- tissue structures are hard to see, es- proach.1 pecially those behind the heart. An overpenetrated CXR looks dark and A: Airway lung markings are hard to see.9 Always look at the When a CXR has good penetration, trachea and assess if the lower thoracic vertebral bodies it’s midline or shifted can be seen through the heart.10 to the right or left. The trachea should Chest X-ray interpretation be midline but may Recognizing normal anatomy on the shift slightly to the CXR is key to understanding and right around the interpreting abnormalities. Before aortic notch.8 If the interpreting a CXR, identify the pa- trachea is shifted or tient by first and last name and date deviated, it may in- of birth. Verify that you have the cor- dicate improper pa- rect X-ray taken on the correct date tient positioning, and identify the view of the CXR. thyroid enlargement, Most facilities now use a digital or a tension pneu- image instead of photographic film mothorax.4,6 costovertebral angle. The anterior contained in a cassette. These digital Next, examine the carina (the area ribs appear more horizontal.4 images are stored on a picture ar- where the trachea bifurcates into the When reviewing the ribs and oth- chiving and communication system right and left bronchi). It should lie er bones, examine the intercostal (PACS). Images from the PACS can be between T4 and T6. If the patient is spaces for symmetry. Remember that viewed at any computer workstation, endotracheally intubated, examine each intercostal space is numbered and they can be manipulated to the CXR for correct tube placement. according to the rib above it. Wid- change brightness or magnify images.2 The endotracheal tube (ETT) is cor- ened intercostal spaces may be asso- Make it a habit to always view the rectly placed when the tip of the ETT ciated with hyperinflation of the CXR as if the patient is facing you; is 3 to 5 cm (approximately 2 in) lungs.2 the right side of the CXR is the pa- above the carina.4 tient’s left side, and vice versa.2,4 C: Circulation Next, determine the quality of the B: Bones Examine the heart for normal size CXR. Is there good penetration? If When looking at the bones on a and shape. One of the easiest obser- so, the thoracic vertebral bodies will CXR, pay close attention to the clavi- vations to make is the cardiothoracic be visible. Is there good inspiration? cles, ribs, scapulae, and vertebrae, ratio: the widest horizontal width of Remember to count the ribs. Deter- and assess for any fractures. Some- the heart compared to the widest mine rotation by measuring the dis- times turning the CXR on its side can width of the thorax.8 The heart tance from the medial end of each help make rib fractures easier to see.8 should be 50% the size of the thorax. clavicle to the spinous process of the On a CXR with maximum inspira- Anything greater than 50% suggests vertebrae at the same level. These tion, expect to see 9 to 10 posterior cardiomegaly or a possible pericar- distances should be equal.4 Anterior ribs.2 In order to tell the difference dial effusion.4 structures on a CXR are the right between anterior and posterior ribs Also examine the mediastinum. Its and left heart borders, the ascending on the CXR, remember that posterior borders should be clear, although aorta, bilateral upper lung lobes, and ribs slope downward to form the some haziness may be present at the www.Nursing2014.com January l Nursing2014 l 43

Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. angle between the heart and dia- Below the left hemidiaphragm, the tion, fluid tends to settle in the phragm.1,8 If the mediastinum ap- gastric air bubble is visible. Absence lower lobes posteriorly.5 pears enlarged, consider disorders of a gastric bubble could indicate a The lung fields should be of equal that could cause this, such as an aor- hiatal hernia.5 density; one shouldn’t be lighter or tic aneurysm.5 darker than the other on a normal E: Edges CXR. Remember that the lungs are D: Diaphragm Inspect the lung borders (edges) for divided into lobes by fissures. The The diaphragm is dome-shaped and fluid or air collection. Look specifi- right lung has three lobes and the has the same density as water. The cally at the costophrenic angles, left lung has two lobes. Try to find right hemidiaphragm should be which should have well-defined acute the horizontal fissure of the right higher than the left because of the angles.8 A pneumothorax, hemotho- lung when looking at the CXR. A liver. (See Visualizing the diaphragm.) rax, or pleural effusion can distort the fissure is a space between the lung The difference should be only about normal lung edges or borders.5 lobes that looks like a narrow white 3 cm. The outline of the diaphragm line on a CXR.2 This fissure, which should be smooth.8 F: Fields can be difficult to visualize, is seen Diaphragmatic elevation occurs The lung fields consist mainly of in 50% to 60% of patients.5,8 It when fewer than 10 ribs are visible air and very little tissue or blood.2,6 should extend from the right hilum and can be caused by atelectasis, ab- Remember normal lung anatomy, to the 6th rib in the axillary line. dominal distension, and phrenic including the location of the lobes, The hilum is a triangular area above nerve compression.2 Diaphragmatic when reviewing CXRs.2 Keep in and behind the cardiac border depression is often present when 11 mind that many patients who are where the structures that form the or 12 ribs are visible. A depressed or erect or semierect for the CXR root of the lung, such as the pulmo- flattened diaphragm is often seen in and have fluid accumulation will nary artery and lymphatic vessels, patients who have chronic obstruc- have abnormal fluid accumulation enter and leave the lung.1 A dis- tive pulmonary disease (COPD) or a at the lung bases. If the CXR is tak- placed fissure may indicate pneu- pneumothorax.1,2 en with the patient in supine posi- mothorax.8

Locating devices on a CXR4

Device Proper location on CXR

ET tube 3 to 5 cm (1.18 to 1.97 in) above the carina

Chest tubes All openings of the chest tube are inside the chest wall; tube tip placed anteriorly and superiorly for air (pneumothorax); posteriorly and inferiorly for fluids (pleural effusion)

Nasogastric tube Below the diaphragm with tip and side holes 10 cm (3.94 in) into the stomach

Dobhoff feeding tube Tip should be in the duodenum (confirmed with abdominal X-ray)

Central venous catheter and peripherally Tip should be in the superior vena cava, above the right atrium inserted central catheter

Temporary double-lumen hemodialysis catheter Tip should be in the superior vena cava

Pulmonary artery catheter Tip should be in the proximal left or right pulmonary artery about 2 cm (0.79 in) from hilum

Intra-aortic balloon pump Tip should be in the descending aorta, distal to the origin of the left subclavian artery

Temporary single-lead transvenous pacemaker Tip is usually located in the apex of the right ventricle

Implantable cardioverter defibrillator Leads should be in the superior vena cava or brachiocephalic vein, and the apex of the right ventricle

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Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Once the CXR has been reviewed costrophrenic an- in a systematic fashion, examine the gles and lateral Kerley B lines CXR for devices such as catheters, wall.2 In this close view of the right lower lung in a patient tubes, drains, or wires. Get into the Pneumonia can with heart failure, Kerley B lines appear as horizontal lines running to the edge of the lung. habit of checking their position. (See best be found on a Locating devices on a CXR.) CXR when a silhouette sign is re- Common abnormalities vealed. A silhou- The following disorders are com- ette sign occurs monly seen in acute care settings and when two struc- may be visible on CXRs. tures of equal den- Pleural effusions are excess fluid sity are next to collections in the pleural space. In each other but the order for a pleural effusion to be border of neither visible on a CXR, approximately structure can be 200 to 400 mL must be present. A seen. (See Silhou- clue that a pleural effusion is pres- ette sign.) The sil- ent is blunting of the costophrenic houette sign is angle.1 A right-sided pleural effu- sometimes used to sion is often associated with heart distinguish ante- failure.5 However, bilateral pleural rior from posterior effusions are present in 70% of pa- structures on a tients with congestive heart failure CXR. The silhou- (CHF).9 ette sign can help Pulmonary edema is the most the practitioner common pattern of diffuse lung dis- determine which ease in patients with CHF.1,6 A dif- lung lobe is affect- fuse lung disease pattern will always ed.8 However, involve both lungs but may involve pneumonia can only part of each lung. Acute pul- also present as a monary edema is the rapid collec- localized infiltrate, tion of an abnormal amount of fluid opacity, or consoli- in the alveoli or pulmonary intersti- dation.2 These in- tial spaces.1 As the amount of fluid filtrates can affect increases in the alveoli, the fluid can any lobe. ambulate, and perform incentive cause a butterfly or batwing pattern to When attempting to decide which spirometry.2 appear on the CXR. This pattern lobe the infiltrate occupies, look for To distinguish between consolida- causes the central or perihilar area of the silhouette sign. When the silhou- tion in pneumonia and consolidation the lungs to appear white. If this ette sign is seen in the anterior struc- atelectasis, assess lung volume. If process goes unnoticed and pro- tures, the pneumonia is in the left or lung volume is reduced, the consoli- gresses, the image on CXR will look right upper lobe of the lung.5 If the dation indicates atelectasis. If not, it like ground glass.1,2 A ground-glass silhouette sign obscures the border of may be due to an infiltrate.8 appearance may indicate overhydra- the right or left hemidiaphragm, this Left lower lobe atelectasis, which tion, heart failure, aspiration pneu- indicates a lower lobe pneumonia. is very common after surgery, often monia, an infectious process, or When the right lower lobe border is appears on a CXR as an increase in even acute respiratory distress syn- lost but the right hemidiaphragm is density.2,4,5 Keep in mind that a lat- drome (ARDS).2 visible, a right middle lobe pneumo- eral view CXR may be needed to Kerley B lines can also be seen on nia is present.8 confirm atelectasis of a lower lobe.2 a CXR in a patient with pulmonary Atelectasis causes the alveoli to When reviewing the CXR, note that edema. (See Kerley B lines.) These are lose their volume and collapse and in consolidation from atelectasis, the thin, horizontal lines of fluid, no may lead to pneumonia. It can be alveolar spaces can become filled more than 2 cm long, which can be prevented or alleviated by having with fluid, causing the alveoli to ap- seen in the lung periphery near the the patient deep breathe and cough, pear white and collapse. www.Nursing2014.com January l Nursing2014 l 45

Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Close inspection of a consolida- Examine the apex of each lung in tion may reveal an air bronchogram detail, as air will always rise while sign. This is a tubular outline of an the patient is in an erect position.4 airway made visible by filling of the Pneumothoraces can occur sponta- surrounding alveoli by fluid or in- neously or be caused by the insertion flammatory exudates. This will cause of central venous access devices, the airway to appear black against a trauma, bleb rupture, or chest com- white background.8 pressions during CPR.5 Intrinsic obstruction can cause Tension pneumothorax occurs atelectasis and is usually a result of when air leaks from the lung into the secretions or foreign bodies in the pleural space and can’t escape, in- airway. Extrinsic airway obstruction creasing intrapleural pressure. This is usually caused by compression, causes the affected lung to collapse likely from a tumor. The most com- and shifts the mediastinum toward mon lobe to become atelectatic is the the unaffected side.4 The mediastinal right middle lobe, due to the lung shift impairs cardiac filling and can being surrounded by lymph node quickly lead to cardiovascular col- tissue and the slope and length of the lapse. Usually, mediastinal landmarks 1 CXRs should always be bronchial tube. taken during maximum such as the trachea, aortic notch, and ARDS is indicated when a normal the right heart border are clearly seen inspiration to allow 8 CXR progresses to one showing bi- visualization of any displaced to the unaffected side. lateral infiltrates, then pulmonary pulmonary abnormalities. COPD includes emphysema and edema. This is likely caused by cel- chronic bronchitis. This type of lung lular damage due to an inflammatory disease causes airway obstruction, air response or events such as trauma.4 trapping, and increased residual vol- Fluid-filled alveoli result in alveolar CXR than fluid, especially if only a ume.4 A flattened diaphragm associ- consolidation in the periphery of the very small amount of air is present. ated with hyperinflation of the lung lung fields. This tends to happen Look for an increase in radiolucency is often the best indicator of COPD within a 12-hour time frame after (dark images on the CXR) and a on a CXR. You may also notice that injury to the alveoli-capillary mem- decrease in lung vascular markings.4 the lungs look very black because of brane.2,8 Whiteout or ground glass The visceral pleura may be dis- vascular destruction. The black ap- opacities on a CXR may follow pe- placed from the parietal pleura due pearance of the lung is called hyper- ripheral consolidation.4 to air in the pleural space. If this is lucency.8 Pneumothorax is caused by air in the case, a thin white line would Hyperinflation of the lungs also the pleural space, which can at represent the displaced visceral cause the lungs to appear larger, times be more difficult to find on a pleura.2,5 darker, and longer.4 It’s also impor- tant to look for bullae on a CXR of a Silhouette sign patient with COPD. These bullae are The patient’s previous X-ray is on the left; in the follow-up X-ray at right, the densely black areas of the lung, usu- silhouette sign is visible as middle-lobe infiltrates obscure the border of the heart. ally round and surrounded by fine curvilinear shadows.8 They’re usually caused by air trapping.4

Other lung disorders The following disorders, although not as common, are also visible on CXR. Lung nodules are discrete areas of whiteness within the lung field. They’re usually less than 3 cm in di- ameter and can be singular or found in multiples. If a lesion is larger than 3 cm, it’s called a mass.5,8

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Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. The main worry about finding Perforation of the bowel is seen as 2. Siela D. Chest radiograph evaluation and interpretation. AACN Adv Crit Care. 2008;19(4): these lesions is the possibility of car- free air under the diaphragm on a 444-473. 8 cinoma. Other possibilities are areas CXR. Air should never appear in the 3. International Atomic Energy Agency. Radiation of consolidation, an abscess, or pleu- peritoneal cavity outside the gastro- safety. http://www.iaea.org/Publications/Booklets/ ral abnormality. Inspect the lesions’ intestinal tract. If air is found in this Radiation/radsafe.html. 4. Ku V. A fresh look at chest X-rays. Nurs Crit Care. edges. A speculated, irregular, or lob- location, it’s called pneumoperito- 2012;7(6):23-29. ulated edge may indicate a malig- neum, which is a medical emergency. 5. Puddy E, Hill C. Interpretation of the chest nancy, especially if you see more than It can be caused by a ruptured ap- radiograph. Contin Educ Anaesth Crit Care Pain. 2007; 7(3):71-75. 8 one. Large masses found in the up- pendix, perforated ulcer, or ruptured 6. Barkley T, Myers C. Practice Guidelines for Acute per lobes are likely to be malignant.4 diverticulum.4 Care Nurse Practitioners. 2nd ed. St. Louis, MO: Malignant tumors may be associated Elsevier; 2008. 7. Siela D. Using chest radiography in the intensive with mediastinal lymphadenopathy Nursing implications care unit. Crit Care Nurse. 2002;22(4):18-27. or bone metastasis. If the nodule ap- Nurses can use CXRs as an addition- 8. Corne J, Pointon K. Chest X-ray Made Easy. 3rd pears dense and white and appears to al tool to confirm physical assess- ed. St. Louis, MO: Elsevier; 2010. be the same density as bone, it’s most ment findings. Acutely ill patients 9. Rull G. Chest X-ray: systematic approach. 2011. http://www.patient.co.uk/doctorChest-Film-(CXR)- 4,8 likely a calcification. can have a multitude of nonspecific Systematic-Approach.htm. Tuberculosis (TB) is seen as signs and symptoms. Nurses with a 10. Dick E. Chest X-rays made easy. Student BMJ. patchy, nodular infiltrates on a CXR basic understanding of CXR interpre- 2000;8:316-317. located primarily on the upper lobe tation can sharpen their assessment William Pezzotti is a critical care NP at The Chester lung fields. Cavitation of the lung, or skills, promote patient safety, and County Hospital in West Chester, Pa. a darker gray center over a white le- optimize care. ■ sion on the CXR, is also seen with The author and planners have disclosed that they TB. An old and healed TB lesion ap- REFERENCES have no financial relationships related to this article. 1. Tarrac SE. A systematic approach to chest x-ray pears on a CXR as a well-defined, interpretation in the perianesthesia unit. J Perianesth 4 dense nodule with sharp margins. Nurs. 2009;24(1):41-47. DOI-10.1097/01.NURSE.0000438704.82227.44

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