Special Interest Section

X-Ray Interpretation for the Student and Novice NNP: An Educational Update.

Valerie Moniaci, DNP APRN NNP-BC

One of the many skills a neonatal nurse practitioner (NNP) must acquire is the ability to interpret X-rays. NNPs often are the first to evaluate an X-ray due to their presence in the neonatal intensive care unit (NICU). Ultimately, the final read is the responsibility of the radiologist, and certainly verification of findings should always be confirmed by radiology. However, there are frequently circumstances when the NNP must provide an initial evaluation of the X-ray to provide appropriate treatment of the many conditions that impact the newborn.

X-rays are commonly ordered to confirm placement of lines and tubes, identify disease states, and to evaluate complications of care such as free air and/or fluid collections. Additionally, evaluation of bony structures, determining the size and shape of the heart, and evaluating intestinal gas patterns are important in a thorough evaluation of an X-ray. In order to most effectively and efficiently evaluate all the components on an X-ray, it is imperative that the NNP is knowledgeable of the many disease processes impacting the newborn and is able to evaluate the X-ray in a systematic manner. The systematic evaluation ensures that each component is evaluated every time an X-ray is completed before decisions are made to proceed forward with therapies or treatment.

Each time an X-ray is ordered, one must understand the risk of radiation exposure in these tiny developing neonates. Over the course of their NICU stay, patients may be subjected to as many as 32 films in the evaluation and treatment of their disease state (Edison et al., 2017; Yu, 2010). Besides X-rays, patients are also often exposed to MRIs and CT scans, which exponentially increase the radiation exposure. Each time a film is ordered, NNPs must ask themselves, “What relevant information can be obtained from this film?” and “Will it provide additional information regarding the diagnosis and management for this patient?” Like all aspects of medicine, the risk benefit of obtaining a film should always be considered. There are significant costs associated each time an X-ray is performed and interpreted, so it is important to be mindful of the impact multiple films have on the patient from a financial perspective (Slovis, Strauss, & Frush, 2011).

In the NICU, films are often ordered on a routine basis (daily, weekly, or monthly) to “follow up” on disease states or placements of endotracheal tube (ETT) or peripherally inserted central catheters (PICC). There is no added benefit to obtaining daily films on ventilated newborns, as it provides information at one point in time that may not be clinically relevant hours down the road. In the absence of clinical changes, or without evidence that lines or tubes have moved, daily films only provide additional radiation exposure without a lot of new information. Clinical examination is an essential component to aid in determining the necessity of X-ray or other types of testing. When in doubt, obtain a second opinion prior to jumping to additional X-rays (Kumar, 2008).

X-Ray Basics

Air displays as black on an X-ray, so the lungs, stomach bubble, and intestinal gas are dark on film. Fluid displays as white, so the heart, thymus, vessels and other vascular findings will display as white. Remaining structures show up as varying shades of grey. Bone and metal fragments absorb X-ray protons and appear as white. The heart and thymus are prominent after birth, and at approximately 24 hours of life, the thymus involutes, making it much less obvious on the films.

Air will rise within the body and is frequently used to aid in the diagnosis of disease states, such as an intestinal perforation. Obtaining a left lateral decubitus film (right side of the body is in the upright position and the film is shot from front to back) provides a scenario where air will rise above and outline the liver, identifying intestinal perforations.

Ribs correspond to vertebrae (as long as there are 12 ribs), so one can count the number of ribs (either top to bottom or bottom to top) to aid in determining appropriate line or ETT placement. The ETT should be positioned below the thoracic inlet (typically at thoracic vertebrae 2 (T2) and above the carina, generally at T4.

Safety factors should be considered each time an X-ray is taken. Minimizing exposure by using gonad shields for the patient and lead shields for the nursing staff are of the utmost importance. Maintenance of thermal stability during the procedure is imperative to minimize complications of cold stress for the baby.

Systematic Approach

A systematic approach to interpreting X-rays is important to make sure that one does not become focused on the one area they are interested in (line placement, ETT placement etc.) and inadvertently ignore other unexpected findings on the film. Becoming focused on looking for the placement of lines, for example, may prevent the viewer from recognizing the large pneumothorax that was unexpected, yet present.

This approach varies among professionals, making it important for the individual to develop an approach that is comprehensive and consistent so that the entire film is evaluated each time a film is obtained. The approach should include the following: 

• Verify correct patient, date, timing of film, and label defining right or left sides.
• Evaluate the quality of the film (rotation / exposure / obstruction of structures).
• Evaluate soft tissue.
• Review bony framework.
• Evaluate lung fields and the mediastinum.
• Evaluate the diaphragm.
• Evaluate solid organs.
• Evaluate abdominal contents / gastrointestinal tract.
• Identify and verify tube and line placements.
• Compare new to prior films to determine resolution or advancement of disease.
• Identify common characteristics suggesting a diagnosis.
• Develop a conclusion / interpretation.

Disease Processes

Common respiratory diseases that affect the newborn each have their own distinct features on an X-ray. Respiratory Distress Syndrome (RDS), or surfactant deficiency respiratory distress, is described as a reticulogranular, or ground glass, appearance of the lungs. The lung volumes (lung expansion) may be low. Air bronchograms are typically present and reflect air in the bronchial tree that is superimposed over atelectatic alveoli. The lungs appear white in color, and in the worst cases, it is difficult to differentiate lungs tissue from cardiac tissue.

Transient Tachypnea of the Newborn (TTNB) presents itself when lung fluid is not adequately expelled during the birthing process and remains in the lungs. These X-rays reveal a prominent hilum with streaky shadows. Fluid may be present in the interlobar fissures (spaces between lung lobes). The heart may be enlarged and lung volumes can be normal to increased (Kumar, 2008).

Meconium Aspiration Syndrome (MAS) presents with “fluffy” opacities interspersed throughout the lungs. Hyperinflation occurs as the meconium plug creates a ball-valve effect where gases are able to enter the lungs on inspiration, but air becomes obstructed by the meconium on exhalation, leading to excessive expansion of the lungs. Air leak syndromes are common with this diagnosis, so monitoring for pneumothoraces is imperative (Kumar, 2008).
Pneumonia commonly presents with patchy infiltrates and areas of consolidation. Lung volumes can be normal to increased. Air trapping is common (Kumar, 2008).

Pulmonary interstitial emphysema (PIE) is a common complication of ventilator therapy frequently impacting the premature patient population. It presents as a honeycomb appearance of translucencies that extend throughout the lung fields. Blebs are common and the lungs are generally hyper expanded.

There are common findings on X-rays that may lead one to a specific diagnosis. When evaluating the heart, for example, a snowman appearance can suggest the infant may be suffering from total anomalous pulmonary venous return (TAPVR). Boot shaped hearts would lead one to consider tetralogy of fallot (TOF), and the appearance of an egg on a string often suggests transposition of the great arteries (TGA). Additionally, endocardial cushion defects present with a goose-neck shape, while Ebstein anomaly resembles a box-shaped heart (Ferguson, Krishnamurthy, & Oldham, 2007).

When reviewing the abdominal component of the film, dilated loops of bowel provide a concern for intestinal obstruction. Dilation of proximal loops leading to the absence of intestinal air beyond the area that is dilated is very concerning for obstruction or blockage beyond that point. The classic double bubble sign is commonly seen in duodenal atresia. A nasogastric tube (NG) that is inserted and either meets obstruction or curls in a pouch will lead to a concern for esophageal atresia. Pneumatosis is the classic finding in necrotizing enterocolitis (NEC) and occurs when air is identified within the bowel wall, leading to a line of what is called railroad tracking. Portal venous gas is the presence of gas within the liver. Babies who present with portal venous air generally have a more severe case of NEC (Markiet, K et al., 2017).

Common X-Ray Views

It is important to order the appropriate view for the film that will provide the best answers for the diagnosis that is being considered. Views provide different information, so it is important to understand which view to order. Infants should be positioned according to the film ordered, tubing and objects should be removed out of the beam field (remember to check under the baby), arms should either be straight to side or held upwards. Midline position of the body helps to minimize rotation, which can impact interpretation of results (clavicles and ribs should be even when comparing the right to left side of the chest).

In the anteroposterior view (AP), the patient is positioned supine and the film is shot from the front to the back. In a cross table lateral view, the patient is positioned supine and the film is shot from side to side. Cross table lateral films are commonly ordered along with the AP for new admissions or for verification of tubes and lines or air within the mediastinum. For this view, the patient is positioned supine and the film is shot from side to side.

With lateral decubitus films, the patient is positioned with either the left or right side up and the film is shot from the front to the back. These type of films are generally ordered to evaluate for the presence of free air, such as that found with intestinal perforation.

A babygram film is one that includes the entire body. It is typically ordered when multiple sections of the body need evaluation and are frequently ordered on admission of critical newborns. The patient is positioned supine and the film is shot from front to back.

Technical Information/Common Terms

• Cardiothoracic ratio: If the size of the heart occupies greater than 65% of the width of the chest, then it is felt to be large and may indicate underlying cardiac anomalies or dysfunction.
• Carina: The point at where the trachea bifurcates into the right and left mainstem bronchus. Typically located at the 3rd to 4th thoracic vertebrae.
• Expiratory films: Films taken during expiration, giving the appearance the of increased heart size, increased lung markings, and decreased lung expansion.
• Exposure: Related to the amount of radiation utilized to obtain the film. Most institutions have strict guidelines regarding appropriate amounts of radiation for the size of the patient. 
• Football sign: Seen in cases of massive pneumo-peritoneum where the abdominal cavity is outlined by gas from the perforated intestine. Signature characteristics show elevation of the falciform ligament.
• Interlobar pulmonary fissures: The space between the lobes of the lungs are not generally seen on a routine film, but if present, represent retained fetal lung fluid, such as that seen with TTN.
• Inspiratory films: Shot during inspiration and provide the best, most accurate information. 
• Lucency: Areas on the film that are transparent.
• Lung hyper-expansion: When counting the rib spaces, the lungs are considered to be excessively expanded when the lungs expand greater than 9 ribs. The diaphragm may also be flat (instead of dome-shaped), indicating increased expansion of the lungs. 
• Lung under-expansion: When counting the rib spaces, the lungs are considered to be poorly expanded when they only expand up to 7 ribs. 
• Opacity: Non-transparent area of the lung. Occurs with areas of atelectasis as with mucus plugging or pneumonia scenarios. 
• Over-penetration: Films that are over penetrated look “dark” throughout the film. This obscures structures and may falsely give the appearance of free air.
• Perihilar: Area surrounding the mediastinal structures. It is normal to see bronchi in this area.
• Pulmonary vascular markings: Can either be diminished or increased depending on the amount of blood flow. Increased pulmonary vascular markings represent increased blood flow dilating the cardiac chambers. Seen with left to right shunting, which occurs with certain congenital heart disease (CHD) and also symptomatic patent ductus arteriosus (PDA).
• Rotated films: Poorly shot films where the body is moved slightly one direction or the other. In this situation, certain structures can be obscured and can appear either smaller or larger in size.
• Sail sign: Occurs when the thymus becomes elevated due to the presence of mediastinal air. 
• Skin folds: Are commonly seen on a film and can mimic free air by creating a line along the edges of the abdominal border.
• Under-penetration: In this situation, the film appears globally lighter in appearance. This gives the appearance of increased fluid in the lungs and other structures. 

Expected placement for lines and tubes

• Endotracheal tube: Positioned below the thoracic inlet and above the carina (thoracic vertebrae 2 - 4). Generally, 1 to 2 cm above the carina (Uceda, 2015).
• Nasogastric tube: Seated within the stomach.
• Umbilical arterial line: High positioned lines—T 6-9 (catheter tip above the celiac axis). Low positioned lines—Lumbar (L) vertebrae 3–4 “below major aortic branches such as renal mesenteric arteries” (MacDonald, MG., Ramesethu, J., & Rais-Bahrami, K., 2013; Fleming, SE. & Kim, JH, 2011).
• Umbilical venous line: High positioned lines—T 9–10 with catheter tip above the diaphragm in the inferior vena cava (IVC). Confirmation of tip placement above the diaphragm is best seen on a lateral view.9
• Percutaneous Central Venous Catheter (PICC): Lower limb PICC target zone T 9–11. Upper limb PICC should sit within the cavo-atrial junction. 

Conclusion

Time, experience and exposure will provide the student and novice NNP with the tools they need to become successful in X-ray interpretation. Developing a systematic approach that works well for the individual and is inclusive of stated components will allow individuals to make an appropriate diagnosis and offer standard treatments for the identified disease process or complication.

References

Edison, P., Chang, P. S., Toh, G. H., Lee, L. N., Sanamandra, S. K., & Shah, V. A. (2017). Reducing radiation hazard opportunities in neonatal unit: Quality improvement in radiation safety practices. BMJ Open Quality, 6(2). doi:10.1136/bmjoq-2017-000128.

Ferguson, E. C., Krishnamurthy, R., & Oldham, S. A. A. (2007). Classic imaging signs of congenital cardiovascular abnormalities. Radiographics: A Review Publication of the Radiological Society of North America, Inc., 27(5), 1323–1334. doi:10.1148/rg.275065148.

Fleming, S. E. & Kim, J. H. (2011). Ultrasound-guided umbilical catheter insertion in neonates. Journal of Perinatology, 31(5), 344-349. doi:10.1038/jp.2010.128.

Kumar, P. Neonatal Chest X-ray interpretation. (2008). Retrieved from: https://www.newbornwhocc.org/pdf/X-rays.pdf.

MacDonald, M. G., Ramasethu, J. & Rais-Bahrami, K. (2013). Atlas of procedures in neonatology. Retrieved from http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=booktext&NEWS=N&DF=bookdb&AN=01641744/5th_Edition&XPATH=/PG(0).

Markiet, K., Szymanska-Dubowik, A., Janczewska, I., Domazalska-Popadiuk, I., Zawadzka-Kepczynska, A., & Bianek-Bodzak, A. (2017). Agreement and reproducibility of radiological sings in NEC using The Duke Abdominal Assessment Scale (DAAS). Pediatric Surgery International 33, 335–340. doi: 10.1007/x00383-016-4022-y.

Slovis, T., Strauss, K., & Frush, D. (2011). How many strikes does it take till we are out? Pediatric Radiology, 41(5), 547–548. doi:10.1007/s00247-011-2016-4.

Uceda, D. (2015). Survival radiology: Neonatal chest X-ray for residents. European Congress of Radiology. doi:10.1594/ecr2015/C-2351.

Yu, C. (2010). Radiation safety in the neonatal intensive care unit: Too little or too much concern? Pediatrics & Neonatology, 51(6), 311–319. doi:10.1016/S1875-9572(10)60061-7.