11: Imaging Studies

The need for radiographs must always be weighed against the risks of exposure of the neonate to radiation (eg, 3–5 mrem per chest radiographic view). The infant's gonads should be shielded as much as possible, and any person holding the infant during the x-ray procedure should also wear a protective shield. For the usual vertically oriented radiographic exposure, personnel need to be only 1 ft outside the zone of exposure.

1. Chest radiographs

   1. Anteroposterior (AP) view. The single best view for identification of heart or lung disease, verification of endotracheal tube and other line positions, and identification of air leak complications of mechanical ventilation, such as pneumothorax.

   2. Cross-table lateral view. Of limited diagnostic value except to determine whether a pleural chest tube is positioned anteriorly (best for drainage of a pneumothorax) or posteriorly (best for drainage of a pleural fluid collection).

   3. Lateral decubitus view. Best at evaluating for a small pneumothorax or a small pleural fluid collection, as either can be difficult to identify on the AP view. For example, if a pneumothorax is suspected, a contralateral decubitus view of the chest should be obtained. An air collection between lung and chest wall will be visible on the side on which the pneumothorax is present. By contrast, for pleural fluid identification, the same side should be placed down (ipsilateral decubitus). The lateral decubitus view may not be safely obtainable in unstable infants.

   4. Upright view. Rarely used in the neonatal intensive care unit (NICU), but can identify abdominal perforation by showing free air under the diaphragm.

2. Abdominal radiographs

   1. AP view. The single best view for diagnosing abdominal disorders such as intestinal obstruction or mass lesions and checking placement of support lines such as umbilical arterial and venous catheters and intestinal tubes.

   2. Cross-table lateral view. Helps diagnose abdominal perforation, but the left lateral decubitus view is better for this purpose. Abdominal perforations may be missed on the AP and cross-table lateral views if the amount of intraperitoneal air is limited or if the segment of perforated bowel contains only fluid.

   3. Left lateral decubitus view. (With the infant placed left side down.) Best for diagnosis of intestinal perforation. Free intra-abdominal air resulting from bowel perforation will be visible as an air collection between the liver and right lateral abdominal wall.

3. Babygram. A radiograph that includes the whole body or just the chest and abdomen (thoracoabdominal babygram) on a single image. It is most commonly ordered for line placement.

4. Barium contrast studies (barium swallow or barium enema). Barium sulfate, an inert compound, is not absorbed from the gastrointestinal (GI) tract and results in little or no fluid shift.

   1. Indications. The use of barium as a contrast agent is recommended for the following:

      1. GI tract imaging. Barium enema is used to rule out lower intestinal tract obstruction from a variety of causes.

      2. Suspected H-type tracheoesophageal fistula (TEF) without esophageal atresia (type E). Most esophageal atresias can be diagnosed by inserting a radiopaque nasogastric tube; the tube curls up in the blind-ending proximal esophageal pouch. If additional confirmation is required, air can be injected under fluoroscopy to distend the pouch. Barium or other contrast agent injection is rarely required. However, evaluation for the rare H-type TEF requires contrast injection, such as barium, into the esophagus.

      3. Suspected esophageal perforation. Barium swallow is used only if previous studies using low-osmolality water-soluble contrast agents were negative.

      4. Suspected gastroesophageal reflux (GER). The pH probe examination and the reflux nuclear scan more reliably identify and quantitate GER than does the upper GI (UGI) series.

   2. Contraindications. Barium contrast studies are not recommended in infants with suspected abdominal perforation or if the destination of the administered contrast is unknown because barium is irritating to the peritoneum and can result in “barium peritonitis.”

5. High-osmolality water-soluble (HOWS) contrast studies. Formerly widely employed in imaging, HOWS contrast agents have been replaced by low-osmolality contrast agents (LOWS).

6. Low-osmolality water-soluble (LOWS) contrast agents. These agents have many advantages over barium and have replaced high-osmolality contrast agents in neonatal imaging.

   1. Advantages

      1. These agents do not cause fluid shifts.

      2. If bowel perforation is present, these substances are nontoxic to the peritoneal cavity. In addition, they do not damage the bowel mucosa.

      3. If aspirated, there is limited irritation (if any) to the lungs.

      4. They have very limited absorption from the normal intestinal tract and thus maintain good opacification throughout the intestinal tract on delayed imaging.

   2. Disadvantages. None other than a higher cost than barium.

   3. Indications

      1. Suspected H-type TEF.

      2. Suspected esophageal perforation.

      3. Evaluation of the bowel if perforation is suspected.

      4. Unexplained pneumoperitoneum.

      5. Evaluation of “gasless abdomen” in a neonate >12 hours of age.

7. Radionuclide studies. Radionuclide studies provide more physiologic than anatomic information and usually involve a lower radiation dose to the patient compared with radiographic examinations.

   1. Reflux scintiscan. Used for documenting and quantitating gastroesophageal reflux and is comparable to the pH probe examination and superior to the upper GI series. Technetium-99m–labeled pertechnetate in a water-based solution is instilled into the stomach. The patient is then scanned in the supine position for 1–2 hours with a gamma camera.

   2. Radionuclide cystogram. Used for documenting and quantitating vesicoureteral reflux. Advantages over the radiographic voiding cystourethrogram (VCUG) is a much lower radiation dose (by 50–100 times) and a longer monitoring period (1–2 hours). Disadvantages include much poorer anatomic detail; bladder diverticula, posterior urethral valves, or mild reflux cannot be reliably identified. This technique should not be the initial examination for evaluation of the lower urinary tract, especially in boys.

   3. Radionuclide bone scan. Used for evaluation of possible osteomyelitis. This procedure involves a 3-phase study (blood flow, blood pool, and bone uptake) after intravenous injection of technetium-99m–labeled methylene diphosphonate.

      1. Advantages. Sensitivity to bony changes earlier than with the radiograph.

      2. Disadvantages. Several. A bone scan may not identify the acute phase of osteomyelitis (ie, the first 24–48 hours), and it requires absence of patient motion, gives poorer anatomic detail than radiographs, and has resultant areas of positive uptake (“hot spots”) that are nonspecific.

   4. HIDA (hepatobiliary) scan. Used in certain types of neonatal jaundice to assist in differentiating biliary atresia (surgical disorder) from neonatal hepatitis (medical disorder).

1. Ultrasonography of the brain. Performed primarily to rule out intraventricular hemorrhage, ischemic change (periventricular leukomalacia [PVL]), hydrocephalus, and developmental anomalies. It can be performed in any NICU with a portable ultrasound unit. No special preparation is needed. However, open anterior and posterior fontanelles must be present, and no intravenous catheters should be placed in the scalp. The AAP recommends that routine cranial ultrasound be performed on all infants <30 weeks' gestation once between 7 and 14 days of age and be repeated between 36 and 40 weeks postmenstrual age. The classification of intraventricular hemorrhage (IVH) based on ultrasonographic findings is demonstrated in Figures 11–1, 11–2, 11–3, and 11–4. Figure 11–5 shows a posterior fossa hemorrhage, and Figure 11–6 demonstrates ischemic changes of PVL. Grading of IVH in the neonate by sonography is as follows (based on Papile, 1978):

   1. Grade I. Subependymal, germinal matrix hemorrhage.

   2. Grade II. Intraventricular extension without ventricular dilatation.

   3. Grade III. Intraventricular extension with ventricular dilatation.

   4. Grade IV. Intraventricular and intraparenchymal hemorrhage.

2. Abdominal ultrasonography. Useful in the evaluation of abdominal distention, gall bladder disease, biliary obstruction, intraperitoneal fluid, abdominal masses, abscesses, and possible causes of renal failure. Abdominal sonography can be performed portably. The addition of duplex and color Doppler evaluation of regional vessels is a supplementary procedure that can identify portal hypertension and vascular occlusion resulting from thrombosis.

3. Power Doppler sonography. Better demonstrates amplitude of blood flow compared with color Doppler but does not define direction of blood flow and is very motion sensitive.

1. CT scanning of the head. More complicated than ultrasonography because the patient must be moved to the CT unit and may require sedation. However, as CT scanning times progressively decrease due to technical improvements, the need for sedation is decreasing. CT scanning provides more global information than ultrasonography of the head, particularly at the periphery of the brain.

2. This technique can be used to diagnose intraventricular, subdural, or subarachnoid bleeding and cerebral edema or infarction. To diagnose cerebral infarction, infusion of contrast medium is necessary. If contrast is used, blood urea nitrogen and creatinine levels must be obtained before the CT test to rule out renal impairment, which may be a contraindication to the use of intravenous contrast media. An intravenous catheter must be placed, preferably not in the head.

3. Imaging for the encephalopathic term infant. Noncontrast CT should be done in an encephalopathic term infant with birth trauma, low hematocrit (Hct), or coagulopathy. This should be done early to rule out hemorrhage.

Now an acceptable mode of imaging in the neonate, and its use is expanding. MRI is superior to CT for imaging the brainstem, spinal cord, soft tissues, and areas of high bony CT artifact. Supplemental magnetic resonance arteriography and magnetic resonance venography are now available to improve vascular anatomy and flow. In encephalopathic term infants, do an MRI if CT findings are inconclusive. MRI is recommended in the first postnatal week to document pattern of injury and predict neurologic outcome.

1. Advantages. The absence of ionizing radiation and visualization of vascular anatomy without contrast agents.

2. Disadvantages. It cannot always be performed on critically ill infants requiring ventilator support, the scanning time is longer, and sedation is usually required.

See Table 11–1 for guidelines for common radiographic studies. Institutional guidelines may vary slightly from these.

Invasive life support and monitoring techniques depend on proper positioning of the device being used. Caution is necessary when identifying ribs and correlating vertebrae in the newborn as a means for determining the proper position of a catheter or tube. Infants often have a noncalcified 12th rib; thus the 11th rib is mistaken for the 12th rib, and an incorrect vertebral count may occur.

1. The preferred location of the endotracheal tube (ETT) tip is halfway between the thoracic inlet (the medial ends of the clavicles) and the carina. Correct tube placement is shown in Figure 11–7.

2. If the ETT is placed too low, the tip usually enters the right main bronchus, a straighter line than with the left main bronchus. The chest film may show asymmetric aeration with both hyperinflation and atelectasis. If the tube extends below the carina or does not match the tracheal air column in position, suspect esophageal intubation. Increased proximal intestinal air may also reflect esophageal intubation. An ETT placed too high has the tip above the clavicle, and the x-ray film may show diffuse atelectasis.

The naso/orogastric tube tip should be in the mid-stomach. Correct placement is shown in Figure 11–8.

The weighted feeding tube is in the mid to distal duodenum. Correct placement is shown in Figure 11–9.

The catheter tip should be at the junction of the inferior vena cava and right atrium, projecting just above the diaphragm on the AP chest radiograph. Degree and direction of patient rotation affect how the UVC appears positioned on the radiograph. Due to its more anterior location, the UVC deviates more from the midline with patient rotation than will the umbilical artery catheterization (UAC). Figure 11–10 shows correct UVC tip placement.

Cochrane review states that high catheters should be used exclusively. In certain instances, a catheter may have to be placed in the low position. The use of high versus low UAC placement used to depend on institutional preference. High catheters were once thought to be associated with a higher risk of vascular complications, but a recent analysis showed a decreased risk of vascular complications and no increased risk of hypertension, necrotizing enterocolitis (NEC), IVH, or hematuria. Low catheters are associated with an increased risk of vasospasms.

1. If high UAC placement is desired, the tip should be between thoracic vertebrae 6 and 9 (above the diaphragm, which is above the celiac axis at T12, the superior mesenteric artery at T12–L1, and the renal arteries [L1]). (Figure 11–11).

2. For low UAC placement, the tip should be below the third lumbar vertebra, optimally between L3 and L4 (above the aortic bifurcation which is at L4–L5) (Figure 11–12). A catheter placed below L5 usually does not function well and carries a risk of severe vasospasm in small arteries. Note that the catheter turns downward and then upward on an abdominal x-ray film. The upward turn is the point at which the catheter passes through the internal iliac artery (hypogastric artery).

   Note: If both a UAC and a UVC are positioned and an x-ray study is performed, it is necessary to differentiate the two so that line placement can be properly assessed. The UAC turns downward and then upward on the x-ray film, whereas the UVC takes only an upward or cephalad direction.

ECLS is a type of external life support using a membrane oxygenator that can be applied to a neonate in severe but reversible respiratory or cardiac failure (see Chapter 18). See VA ECLS cannulae placement and VV ECLS cannulae placement radiographs (see Figures 18–2 and 18–3, respectively).

1. Respiratory distress syndrome (RDS). A fine, diffuse reticulogranular pattern is seen secondary to microatelectasis of the alveoli. The chest radiograph reveals radiolucent areas known as air bronchograms, produced by air in the major airways and contrasted with the opacified, collapsed alveoli (Figure 11–13).

2. Meconium aspiration syndrome (MAS). Bilateral, patchy, coarse infiltrates and hyperinflation of the lungs are present (Figure 11–14). There is also an increased incidence of pneumothorax.

3. Pneumonia. Diffuse alveolar or interstitial disease that is usually asymmetric and localized. Group B streptococcal pneumonia can appear similar to respiratory distress syndrome (RDS). Pneumatoceles (air-filled lung cysts) can occur with staphylococcal pneumonia. Pleural effusions or empyema may occur with any bacterial pneumonia (Figure 11–15).

4. Transient tachypnea of the newborn (TTN). Hyperaeration with symmetric perihilar and interstitial streaky infiltrates are typical. Pleural fluid may occur as well, appearing as widening of the pleural space or as prominence of the minor fissure (Figure 11–16).

5. Bronchopulmonary dysplasia (BPD). Now more commonly referred to as chronic lung disease (CLD), the radiographic appearance is highly variable, from a fine, hazy appearance of the lungs to mildly coarsened lung markings to a coarse, cystic lung pattern (Figure 11–17). Typically occurring in ventilated premature neonates, CLD usually requires a minimum of 7–10 days to develop. Many centers no longer rely on the following grading system for this condition, but it is included for historical purposes.

   1. Grade I. X-ray findings are similar to those of severe RDS.

   2. Grade II. Dense parenchymal opacification is seen.

   3. Grade III. A bubbly, fibrocystic pattern is evident.

   4. Grade IV. Hyperinflation is present with multiple fine, lacy densities spreading to the periphery and with areas of lucency similar to bullae of the lung.

6. Air leak syndromes

   1. Pneumopericardium. Air surrounds the heart, including the inferior border (Figure 11–18). Cardiac tamponade may result.

   2. Pneumomediastinum

      1. AP view. A hyperlucent rim of air is present lateral to the cardiac border and beneath the thymus, displacing the thymus superiorly away from the cardiac silhouette (“angel wing sign”) (Figure 11–19, left panel).

      2. Lateral view. An air collection is seen either substernally (anterior pneumomediastinum) or in the retrocardiac area (posterior pneumomediastinum) (Figure 11–19, right panel).

   3. Pneumothorax. The lung is typically displaced away from the lateral chest wall by a radiolucent zone of air. The adjacent lung may be collapsed with larger pneumothoraces (as in Figure 11–20). The small pneumothorax may be very difficult to identify, with only a subtle zone of air peripherally, a diffusely hyperlucent hemithorax, unusually sharply defined cardiothymic margins, or a combination of these.

   4. Tension pneumothorax. The diaphragm on the affected side is depressed, the mediastinum is shifted to the contralateral hemithorax, and collapse of the ipsilateral lobes is evident (Figure 11–20).

   5. Pulmonary interstitial emphysema (PIE). Single or multiple circular radiolucencies with well-demarcated walls are seen in a localized or diffuse pattern. The volume of the involved portion of the lung is usually increased, often markedly so (Figure 11–21). PIE usually occurs in ventilated preemies with RDS within the initial few days of life.

7. Atelectasis. A decrease in lung volume or collapse of part or all of a lung is apparent, appearing as areas of increased opacity. The mediastinum may be shifted toward the side of collapse. Compensatory hyperinflation of the opposite lung may be present.

   1. Microatelectasis. Nonobstructive atelectasis associated with RDS.

   2. Generalized atelectasis. Diffuse increase in opacity (“whiteout”) of the lungs is visible on the chest film. It may be seen in severe RDS, airway obstruction, if the endotracheal tube is not in the trachea, and hypoventilation.

   3. Lobar atelectasis. Lobar atelectasis is atelectasis of one lobe. The most common site is the right upper lobe, which appears as an area of dense opacity (“whiteout”) on the chest film. In addition, the right minor fissure is usually elevated. This pattern of atelectasis commonly occurs after extubation.

8. Pulmonary hypoplasia. Small lung volumes and a bell-shaped thorax are seen. The lungs usually appear radiolucent.

9. Pulmonary edema. The lungs appear diffusely hazy with an area of greatest density around the hilum of each lung. Heart size is usually increased.

The cardiothoracic ratio, which normally should be <0.6, is the width of the base of the heart divided by the width of the lower thorax. An index >0.6 suggests cardiomegaly. The pulmonary vascularity is increased if the diameter of the descending branch of the right pulmonary artery exceeds that of the trachea.

1. Cardiac dextroversion. The cardiac apex is on the right, and the aortic arch and stomach bubble are on the left. The incidence of congenital heart disease associated with this finding is high (>90%).

2. Congestive heart failure. Cardiomegaly, pulmonary venous congestion (engorgement and increased diameter of the pulmonary veins), diffuse opacification in the perihilar regions, and pleural effusions (sometimes) are seen.

3. Patent ductus arteriosus. Cardiomegaly, pulmonary edema, ductal haze (pulmonary edema with a patent ductus arteriosus), and increased pulmonary vascular markings are evident.

4. Ventricular septal defect. Findings include cardiomegaly, an increase in pulmonary vascular density, enlargement of the left ventricle and left atrium, and enlargement of the main pulmonary artery.

5. Coarctation of the aorta

   1. Preductal coarctation. Generalized cardiomegaly, with normal pulmonary vascularity, is seen.

   2. Postductal coarctation. An enlarged left ventricle and left atrium and a dilated ascending aorta are present.

6. Tetralogy of Fallot. The heart is boot shaped. A normal left atrium and left ventricle is associated with an enlarged, hypertrophied right ventricle and small or absent main pulmonary artery. There is decreased pulmonary vascularity. A right aortic arch occurs in 25% of patients.

7. Transposition of the great arteries. The chest film may show cardiomegaly, with an enlarged right atrium and right ventricle, narrow mediastinum, and increased pulmonary vascular markings, but in most cases the chest film appears normal.

8. Total anomalous pulmonary venous return (TAPVR). Pulmonary venous markings are increased. Cardiomegaly is minimal or absent. Congestive heart failure and pulmonary edema may be present, especially with type 3 (subdiaphragmatic) TAPVR.

9. Hypoplastic left heart syndrome. The chest film can be normal at first but then may show cardiomegaly and pulmonary vascular congestion, with an enlarged right atrium and ventricle.

10. Tricuspid atresia. Heart size is usually normal or small, the main pulmonary artery is concave, and pulmonary vascularity is decreased.

11. Truncus arteriosus. Characteristic findings include cardiomegaly, increased pulmonary vascularity, and enlargement of the left atrium. A right aortic arch occurs in 30% of patients.

12. Atrial septal defect. Varying degrees of enlargement of the right atrium and ventricle are seen. The aorta and the left ventricle are small, and the pulmonary artery is large. Increased pulmonary vascularity is also evident.

13. Ebstein anomaly. Gross cardiomegaly and decreased pulmonary vascularity are apparent. The right heart border is prominent as a result of right atrial enlargement.

14. Valvular pulmonic stenosis. Heart size and pulmonary blood flow are usually normal unless the stenosis is severe. Dilatation of the main pulmonary artery is the typical chest film finding.

1. Changes in the following normal patterns should raise suspicion of GI tract disease.

   1. Air in the stomach. Should occur within 30 minutes after delivery.

   2. Air in the small bowel. Should be seen by 3–4 hours of age.

   3. Air in the colon and rectum. Should be seen by 6–8 hours of age.

2. Intestinal obstruction. Gaseous intestinal distention is present. Gas may be decreased or absent distal to the obstruction. Air-fluid levels are seen proximal to the obstruction.

3. Ascites. Gas-filled loops of bowel, if present, are located in the central portion of the abdomen. The abdomen may be distended, with relatively small amounts of gas (“ground-glass” appearance). A uniform increase in the density of the abdomen, particularly in the flank areas, may be evident.

4. Calcification in the abdomen is most often seen secondary to meconium peritonitis, which may also cause calcifications in the scrotum in male infants. Calcifications in the abdomen may also be seen in infants with neuroblastoma or teratoma, or may signify calcification of the adrenals after adrenal hemorrhage.

5. Pneumoperitoneum

   1. Supine view. Free air is seen as a central lucency, usually in the upper abdomen (Figure 11–22).

   2. Upright view. Free air is present in a subdiaphragmatic location.

   3. Left lateral decubitus view. Air collects over the lateral border of the liver, separating it from the adjacent abdominal wall.

6. Pneumatosis intestinalis. Intraluminal gas in the bowel wall (produced by bacteria that have invaded the bowel wall) may appear as a string or cluster of bubbles (submucosal) or a curvilinear lucency (subserosal). It is most frequently seen in infants with NEC (Figure 11–23).

7. Situs inversus (complete). The stomach, aortic arch, and cardiac apex all are right sided. There is only a limited increased incidence of congenital heart disease.

8. Ileus. Distended loops of bowel are present. Air-fluid levels may be seen on the upright or cross-table lateral abdominal film.

9. Absence of gas in the abdomen. Absence of gas in the abdomen may be seen in patients on muscle-paralyzing medications (eg, pancuronium) because they do not swallow air. It may also be evident in infants with esophageal atresia without tracheoesophageal fistula and in cases of severe cerebral anoxia resulting in central nervous system depression and absence of swallowing.

10. Portal venous air. (Figure 11–24) Air is demonstrated in the portal veins (often best seen on a lateral view). This finding may indicate bowel necrosis, which can occur in an advanced degree of NEC; intestinal infarction secondary to mesenteric vessel occlusion; and iatrogenically introduced gas into the portal vein, which can occur during umbilical vein catheterization or exchange transfusion.