Infants are not small adults. In addition to their physical fragility, they are physiologically distinct and prone to a suite of disorders not seen among adults. Risks associated with exposure to radiation and the injection of contrast agents must be weighed against the probable diagnostic benefits of using a given imaging technique. Because of the administration of radioactive isotope tracers, for example, nuclear medicine imaging plays a limited role in neonatal imaging, compared with adult imaging. Traditional plain-film radiography, ultrasound, magnetic resonance (MR) and computed tomography (CT), on the other hand, all play important roles in neonatal diagnostic imaging.
In this reading, the respective strengths and weaknesses of these techniques for various pediatric radiology applications will be introduced and reviewed, and common neonatal imaging examinations and radiological signs will be described.
History of Pediatric Imaging
Pediatrics and radiologic imaging developed independently as separate disciplines from their inception until the 1950s, when the integrated discipline of pediatric radiology began to take shape in North America and Europe.[1,2] Even in the early years of radiology, however, basic pediatric medicine was a notable application of imaging technologies; the first clinical radiograph in the United States was made in 1896 at Dartmouth College of a boy who hurt his wrist while ice-skating. Pioneering pediatric radiology departments were established in Austria, Canada and the eastern United States during the late 1890s -- primarily to evaluate suspected bone fractures. Until New York pediatrician John Caffey's 1945 text Pediatric X-Ray Diagnosis was published, the scope of pediatric radiography remained largely limited to evaluating bone trauma.
Pediatric radiology has expanded rapidly since the late 1950s and is now a recognized medical specialty. In 1958 the Society for Pediatric Radiology was established. From an original group of 33 radiologists, membership has grown to exceed 1000 today. In recent years, ultrasonography, CT and MR have revolutionized the field.
Skills and Approach
Successful diagnostic imaging of the newborn requires experience and skills distinct from those required for adult patients. From the technologist's basic attitude to learning how to position babies using immobilization tools, these skills make the difference between successful examinations and repeated, prolonged and error-riddled exams that are unpleasant and expensive. Furthermore, the radiologic technologist must be aware at all times of the safety issues and risks faced by the neonatal patient during imaging examinations. In this section, basic skills and practices are introduced.
Infants, while unsophisticated in their communicative abilities, are nevertheless adept mind readers when observing adults. Because of the difficulties involved in imaging young children, radiologic technologists are often uncomfortable working with them. Both parents and the young patient are likely to misperceive this as evidence that something is seriously wrong. A smiling face, on the other hand, is almost always reassuring and calming. Remember the basics: Smile, use the patient's name when addressing him or her and be gentle' and upbeat.
Infants' immune systems are not yet the rigorous defenders against infection that healthy adults have. This is particularly true for premature newborns.
Hands and transducers always should be thoroughly washed before coming into contact with infants. This is absolutely critical when introducing hands or medical equipment into a premature infant's incubator. Hands should be washed with institutionally approved soaps and disinfectants, with attention paid to cleaning cuticles, fingernails and between fingers.
Preparation procedures for specific imaging applications are described in detail below. In all cases, however, radiology personnel should become familiar with the patient's medical history, physical examination and laboratory studies before scheduled examinations. Ideally, this should occur before the day of the scheduled examination.
The request form, patient's chart and the patient's x-ray folder are given to the radiologic technologist for review. Before any examination, the imaging procedure should be explained to the parent or caregiver in a staging area. Policies differ among hospitals, but in some cases parents may be allowed or even encouraged to stay and participate in the exam, particularly if the infant is upset. In the rare event that a parent's presence is more disruptive than helpful, parents should be asked politely to wait outside the area. After the examination, the patient is returned to the staging area while images are processed and checked for quality. Films are added to the x-ray jacket and request form for review by the radiologist.
Warmth is important to newborn comfort, and warming lights should be directed toward the baby during examinations whenever possible. Gels used to attach equipment, such as acoustic couplings, should be warmed. Warmed blankets also may be used to comfort and calm the patient.
The primary cause of poor imaging outcomes is squirming or other movement by the patient. Because infants cannot follow verbal instructions, proper immobilization techniques are critical for good radiographic quality, fewer repeated examinations and shorter examination times. The technologist may require assistance to keep a child immobile for examination. When assistance is necessary, the infant's parent or caregiver should be recruited to help, provided with basic instructions and given a limited, simple task. However, manual restraint (holding the infant down) is often more traumatic and less effective than simply using mechanical immobilization.
Commercial immobilization devices are available at many institutions, or simple Velcro-type restraints may be improvised. (See Fig. 1.) Infants rarely fall asleep during manual restraint, but often will doze while mechanically immobilized, particularly if swaddled with warm blankets. For many imaging applications involving horizontal examination (with the newborn on his or her back), simply placing sand bags around the infant to limit lateral movement will suffice.
Immobilization boards are designed for horizontal radiographic tables, and Velcro-type or plastic adjustable straps can be attached to the board to immobilize arms and legs. Immobilizer boards are used to obtain supine radiographs with perpendicular x-ray beam orientation and supine anteroposterior (AP) and lateral chest radiographs using perpendicular beam or horizontal beam radiography.
Sedation usually is required when intravenous contrast is used. In general, infants with upper respiratory obstruction and cardiac disease should not be sedated. If sedation is absolutely necessary, extreme caution must be observed; the infant must be monitored visually and mechanically throughout the examination, using electrocardiography (ECG) and pulse oximetry.
Whereas children older than 1 year commonly are sedated with pentobarbital, fentanyl citrate or midazolam, neonates should be sedated only when absolutely necessary and then only with chloral hydrate. The recommended dosage varies from 50 to 100 mg chloral hydrate per kg body weight, orally or rectally administered. In all cases of pediatric sedation, the smallest effective dose should be used.4 Because chloral hydrate remains in the body and sedation is maintained until the liver metabolizes it, impaired liver function is a contraindication for the use of chloral hydrate.
An alternative to sedation is pacification. A sanitized pacifier in the infant's mouth often is sufficient to calm a squirming or fussy newborn.
Glucose water in the place of formula calms newborns and makes an excellent pacifier. Glucose has been shown to reduce anxiety and discomfort, and even elevate pain thresholds and shorten crying duration in response to painful procedures like immunization shots. Glucose pacification is an especially useful alternative to sedation for examinations that require the infant to remain still, such as Doppler ultrasound. Bottles of sugar water and hippies should be available in every pediatric radiology or ultrasound suite.
The primary risks associated with pediatric radiology are exposure to radiation, psychological distress, physical trauma, sedation and reactions to contrast media.
Prenatal radiation exposures have been linked to childhood leukemias, and it is generally agreed that there is no completely safe level of clinical radiation exposure for the neonate. Radiographic examination should be undertaken with infants only to address a specific clinical question, and cautious application of proper technique will eliminate the need for multiple follow-up examinations. When follow-up examinations are required, it is important that imaging conditions and patient orientation match those of earlier exams, to allow clinical comparison between films. This is particularly true in mobile imaging units.
Gonadal shielding sometimes is overlooked, despite its critical importance for protecting a patient's later fertility. In addition to gonadal shielding, radiation exposure to the newborn can be reduced by using tight collimation, shielding the breast area and proper patient positioning and immobilization. Radiation exposure also can be minimized by using alternative imaging techniques whenever possible (eg, ultrasound and MR instead of x-ray, CT or scintigraphy), by tailoring examinations to specific diagnostic needs and by avoiding repeat examinations and unnecessary exposures, such as those caused by improper infant immobilization, orientation or film processing.
Administration of contrast agents should be avoided in pediatric radiography whenever possible because of allergic and nephrotoxic response risks. When their use cannot be avoided, patients should be monitored very closely for evidence of allergic reaction. Anaphylactoid reactions occur in 1% to 2% of patients.
Precise radiographic imaging sometimes requires the use of radio-dense (x-ray absorbing) contrast agents with specific organ or tissue affinities. Contrast enhances the ability to demonstrate and differentiate target organs. Barium sulfate and iodine solutions are acceptable contrast agents in neonatal radiography. Radiographic contrasts are injected intravenously, swallowed or administered as enemas. Aspiration is a risk when swallowed contrast agents are administered to the neonate for gastrointestinal tract imaging. Dose is determined by mass and varies between contrast agents and institutions. Contraindications include seizure history or epilepsy, renal insufficiency and a family or patient history of hay fever or other allergy or bronchial asthma.
Nuclear medicine imaging (scintigraphy) involves administration of radioactive isotope tracers with specific target organ or tissue affinities. This internal source of absorbed radiation in newborns warrants special attention by the radiologic technologist. In general, scintigraphy should be avoided with newborns, if possible.
If pediatric nuclear medicine imaging is indicated, radiopharmaceutical dosimetry follows the rule of exposing the infant to the absolute minimum amount of absorbed radiation necessary to obtain a diagnostically useful image. It is important to keep in mind that too low a dose can ultimately lead to greater radiation exposure because inadequate scintigraphic quality results in repeated exams.
Dosages for infants often are calculated by correcting adult dosages for infant body surface area or, more commonly, infant mass. Every institution should have a schedule of approved radiopharmaceutical doses per unit infant mass (usually expressed in kilograms) for pediatric nuclear medicine imaging applications. With newborns, however, body mass is often so low that if standard per kilogram doses are applied, the minimal total dose will not be achieved. (The minimal total dose is that dose below which scintigraphic exams will be diagnostically inadequate due to insufficient contrast). Radiopharmaceutical dose schedules vary by institution, but minimal total doses should be observed in every neonatal scintigraphic exam.
With the increased use of latex gloves due to the HIV/AIDS epidemic, the incidence of latex contact dermatitis and latex hypersensitivity in health care professionals and patients has increased in recent years. These reactions are allergic in nature, with latex antigens provoking immune responses in the skin.
Possibly because of extensive latex exposure in early life, infants with spina bifida are at extreme risk of latex hypersensitivity. These infants should be treated in a latex-free environment. Patients with congenital anomalies of the urogenital tract or spinal injuries also are believed to be at higher risk of latex reactions.
When newborns show evidence of latex allergic reaction, the affected area should be washed and rinsed thoroughly, and an alert bracelet or other alerting system should be used to notify others. If the reaction is severe, a dermatologist should be consulted. Hypoallergenic gloves should be used when handling infants with histories of latex sensitivity.
Imaging Techniques for Pediatric Patients
The major imaging techniques used for adult patients commonly are used with infants as well. Each technique has clinical and economic benefits and weaknesses. For example, plain-film radiography yields a global view of regional anatomy, but lacks the fine level of detail and tissue contrast available with MR and CT. Ultrasound is less invasive and expensive and does not expose infants to radiation, but air and bone can disrupt imaging of target organs. CT and MR offer excellent anatomical detail and tissue contrast, but both can be slow, expensive and require infant sedation.
A given imaging technique should be used only if the diagnostic utility outweighs the drawbacks (eg, exposure to radiation or contrast agents, sedation and patient and parental anxiety). Functional questions, such as whether an infant has impaired renal function, may indicate nuclear medicine imaging, whereas anatomic questions, such as whether a tumor is present, indicate ultrasound, radiography, CT or MR, depending on the target organ and the level of detail required.
In the following sections, common methods of imaging newborns, and the advantages and limitations of each, are introduced. Specific diagnostic applications for each imaging technique will be described in greater detail in the next section.
Mobile x-ray units and portable ultrasound equipment are vital tools in infant radiography. Particularly with preterm infants, who must be kept in incubators that cannot safely or practically be moved from the nursery, mobile or portable radiologic equipment is indispensable. Even in open nursing units, heating panels used with infants often preclude easy transport of the patient to the radiology department, necessitating the availability of easily moved imaging equipment.
Mobile x-ray units should be available in every pediatric radiology department. Mobile units are either battery powered or capacitor-discharge units that plug into wall power outlets. They possess variable, operator-selected kilovoltage (from 55 kV to 120 kV). Tube current should be at least 100 mA for imaging infants, permitting short exposure times for the squirming patient.
Ultrasound involves the transmission of high-frequency sound waves into target regions and transduction of returning sound wave echoes into electrical impulses that are viewed in real time on a television monitor. Different tissues' varying densities cause different levels of sound wave absorption and reflection. Ultrasound rarely requires infant sedation. Pacifiers, feeding or glucose water usually keeps neonates sufficiently still for successful ultrasound examination. For a particularly fussy, restless infant, sandbags can be placed alongside the patient to gently immobilize and position him or her for ultrasound examinations.
Ultrasound is the imaging technique of choice for examinations of the neonatal abdomen, pelvis, cranium and spine, but is rarely sufficient for detailed imaging of the gastrointestinal tract. CT or MR follow-up examinations commonly are required to clarify results of ultrasound exams.
Doppler ultrasound is used to measure movement of tissues, particularly blood flow. Different rates of flow are visible as different colors on the ultrasound monitor.
Echocardiography, ultrasound of the heart, allows measurement of heart dimensions, as well as detailed examination of the complex motion of a beating heart.
Even with advances in ultrasound and MR, radiography remains the chief imaging technique for most neonatal diagnostic imaging applications. However, because of the radiation exposure associated with x-ray examinations, this imaging technique should be used only to answer a specific clinical question that is best addressed by radiography. If ultrasound can obtain the same diagnostic information, it should be used instead.
Plain-film radiography is indicated when investigating problems of the chest, abdomen or bowel and skeleton. Chest radiography is the workhorse for neonatal pulmonary imaging and remains the preferred imaging technique for suspected lung and bone disease.
CT uses x-rays to make sequential cross-sectional images of the body. Acquired data can be used to generate 2- or 3-D images of target organs from different perspectives. CT is indicated during follow-up imaging of intracranial trauma and in cases of hypoxia and hemorrhage. However, MR is indicated when more detailed cranial imaging is needed. CT is not commonly used to examine the chest or abdomen of newborns, unless tumors are suspected. As with traditional radiography, CT sometimes is used with a contrast agent to better differentiate and examine target tissues. However, as discussed above, contrast agents should be avoided in neonatal imaging if possible.
MR uses radiofrequency energy absorption and emission behavior of subatomic particles to yield images with superior soft-tissue contrast. This, in addition to its multiplanar imaging capabilities and lack of ionizing radiation, make MR an attractive alternative for neonatal imaging. However, MR examinations are slow and sedation usually is necessary, particularly in closed MR units (eg, orally administered chloral hydrate at a dose of 50 to 100 mg/kg). Neonatal MR should maximize image quality in the region of interest in as short a time as possible.
MR is indicated when precise anatomical delineation is required, particularly in investigations of the head and spine. It generally is employed to clarify results of ultrasound or CT examinations. In closed MRs, it can be difficult to monitor the infant during imaging. Furthermore, infant anesthesia often is required for MR examinations. Nevertheless, MR is the imaging technique of choice for detailed examinations of intracranial trauma, congenital anomalies, hypoxia-related brain damage and brain stem pathologies.
Angiography is the radiographic study of blood vessels with injected contrast agents. Because MR angiography images vasculature without contrast agents, it is increasingly the preferred technique for angiographic examination.
Fluoroscopy involves real-time viewing of radiographic images on a television monitor. Fluoroscopy allows detailed studies of organ function (such as heart movement) and is used to investigate the gastrointestinal tract. Individual radiographic films can be taken as needed during fluoroscopy, or the entire examination can be videotaped.
Nuclear Medicine Imaging
Neonatal nuclear medicine imaging (scintigraphy) involves detection of administered radiopharmaceuticals. Scintigraphy can provide sensitive imaging of physiological processes and radiographically occult, severe infections. These functional images can assist clinicians in assessing anatomic data from other imaging techniques. Radioactive agents or "tracers" with affinities for specific organ systems usually are administered orally or by injection, and imaged as they accumulate in target tissues or lesions.
Scintigraphy is relatively safe, as long as carefully controlled, appropriate doses of radiopharmaceuticals are used. However, advances in ultrasound technique and the intrinsic risks involved in injecting infants with radioactive isotopes have reduced the use of nuclear imaging for neonates. Though uncommon, there are applications for which scintigraphy is still the best imaging technique.
Diagnostic Imaging of Newborns
Because clinical history and physical examination are much less diagnostic in newborns than with older children or adults, imaging plays a central role in the care of neonates.
Traditional plain-film chest radiography is the single most common imaging examination performed with newborns. Indications for neonatal chest x-ray include clinical evidence of lung pathology or respiratory distress, heart morphology and assessment of medical equipment, such as endotracheal or nasogastric tube positions, chest drains and vascular lines. Chest radiography often is used as a preliminary screening examination and typically is followed up with a more specific technique if signs of disease are present. For example, radiographic signs of congenital heart disease should be verified with echocardiographic examination.
Neonatal chest radiography demands that the radiologic technologist simultaneously pay attention to several factors. These include the need for low exposures (using the minimal effective kV and mAs), minimizing patient movement, monitoring respiratory (or ventilator) rate and the need to avoid disturbing a patient's lines and tubes while working in a very confined space. Even cooperative infants are not as obliging as adults: They squirm and breathe during examinations.
Technologists should be familiar with the following common challenges of pediatric radiography. These include:
* Expiration errors. Chest radiographs imaged during exhalation often are mistakenly thought to show the patient's deteriorating clinical condition and should be avoided. Similarly, apparent changes in lung volume between radiographs may be due to variation in the degree of inspiration during exposure.
* Shallow breath error. If the infant is breathing shallowly, the apparent size of the lungs will be small and the heart can appear to be enlarged.
* Tube-film distance variations. The distance between the tube and film can affect image quality. For example, erect vs supine patient positioning yields an average difference in tube-film distances of 81 cm.
* Density errors. Image density can vary due to exposure factors, and comparing images with different densities can lead to clinical misinterpretation.
* Rotated films. Pulmonary asymmetry, with one lung appearing larger than the other or partially obscured, results from infant movement. Radiologic technologists should pay particular attention to the relative position and orientation of the neonate to avoid rotated images. (See Fig. 2.) Rotation makes assessment of heart size particularly difficult.
Correctly reading a neonatal chest radiograph requires years of experience. One method for reading pediatric chest x-rays is to overlay an imaginary circle over the radiograph. Starting with the corner of the radiograph containing patient information, the radiologist checks the name, date and markers of the patient's left or right side. From the left/right marker, he or she examines visible portions of the newborn's abdomen, then the bones and soft tissues and finally the chest.
Major physiological shifts occur as the newborn lung makes the transition from placental support to independent pulmonary function. Normally, complete filling of the lungs with air occurs within 3 breaths after birth.
Although various grading or scoring systems are used for evaluating neonatal chest radiographs in research studies, these are rarely used in clinical practice and will not be detailed here.
The heart and thymus are the most prominent radiographic features in the first hours after birth. (See Fig. 2.) The newborn heart normally appears more globular than in older children and adults, and the upper limit of the wide range of normal heart-to-thorax volume ratios (the cardio-thoracic index) is 65%. However, because of the imprecision of neonatal cardiothoracic index estimations, they are of questionable value in determining abnormal heart size in infants.
A healthy thymus gland often complicates interpretation of chest x-rays in the first day after birth because it is easily mistaken for cardiac enlargement or, less often, lobar pulmonary collapse. Infants weighing less than 750 g, on the other hand, often have a thymus that appears very small or is not visible at all.
Lung vessels are not normally imaged well and lung surface fissures, which are used to delineate pulmonary lobes in older children and adults, are so indistinct that neonatal radiologists often speak of pulmonary "zones" rather than pulmonary lobes. Indeed, visualization of pulmonary fissures in a chest radiograph may be evidence of transient tachypnea of the neonate (TTN; see below). The newborn's bronchi normally can be seen through the heart. (See Fig. 2.)
Deviations from normal radiographic appearance of the neonatal chest can be subtle and, like clinical signs of neonatal distress, often are nonspecific. In the following subsections, common chest pathologies and their radiologic appearances will be described.
* Respiratory distress syndrome. Half of newborn deaths are due to lung disorders, and the most common neonatal pulmonary disorder is respiratory distress syndrome (RDS).
Grunting during expiration, use of accessory muscles (eg, the abdominal muscles) to breathe, abnormal retraction of the chest wall during respiration and tachypnea (more than 60 breaths per minute) with cyanosis are nonspecific clinical indications of RDS, once known as hyaline membrane disease (HMD). Infants with RDS very often require artificial respiratory support delivered via oxygen mask, continuous positive airway pressure (CPAP) or intermittent positive pressure ventilation (IPPV).
Anteroposterior (AP) radiographs are taken when RDS is suspected. The severity of radiologic abnormality in RDS correlates positively with clinical risk. A normal chest radiograph obtained at age 6 hours rules out RDS.
Classic signs of RDS are granularity of the lungs (sometimes likened to "ground glass"), low-volume lungs or hypoaeration (underfilling) of the lungs resulting in a bell-shaped thorax, and air bronchograms. (See Fig. 3.) Newborns with RDS exhibit a very prominent thymus, with the lateral margin appearing to have a wavy contour ("wave sign"). Severe cases exhibit progressively worse hypoaeration of the lungs and diffuse radiopacities in both lungs.
As RDS worsens, or when RDS occurs simultaneously with pneumonia, lung hemorrhage or congestive heart failure, diffuse opacity and apparent airlessness of the lungs results in a "white-out" sign. (See Fig. 4.)
Other causes of RDS-like surfactant deficiency include asphyxia, maternal diabetes and immature lung syndrome.
* Immature lung syndrome. Premature infants with birth weights less than 1500 g and an absence of respiratory distress until late in the first week after birth (age 4 to 7 days) may have immature lung syndrome.
Immature lungs lack sufficient pulmonary surfactant for proper ventilation of the alveoli, the tiny organs at the distal ends of lung airways that exchange carbon dioxide for oxygen. Diffuse granularity of immature lungs can lead to mistaken diagnosis of RDS, but air bronchograms, which are common in RDS, are rarely present in immature lungs. Nevertheless, some authors believe that RDS is not readily distinguishable radiographically from immature lung syndrome. Both disorders benefit from therapy with an administered exogenous surfactant. Immature lungs often require several weeks of CPAP therapy.
* Pneumonia. Respiratory distress may indicate pulmonary infection (neonatal pneumonia). The newborn's infection is often a result of exposure in utero or during birth. Chest radiography is often the first definitive evidence of infection. Jaundiced skin, poor oxygen perfusion in body tissues and lethargy are additional clinical indications. Early-presentation pneumonia (1 to 5 days after birth) involves respiratory distress and, in some cases, shock due to sepsis. As a result, its radiographic signs are easily mistaken for RDS. Late-presentation neonatal pneumonia (more than 5 days after birth) may involve Staphylococcus epidermidis (although this is not a common neonatal infection) or, particularly in low-birth-weight neonates, Candida species of bacteria. Neither early- nor late-presenting pneumonia should await definitive diagnosis before antibiotic therapy is begun.
Pneumonia results in abnormal, patchily distributed pulmonary densities.[8,13] Infection usually involves the small, distal airways. Bacterial pneumonia often is also indicated radiographically by numerous small, air-filled areas known as pneumomatoceles. (See Fig. 5.)
Chlamydia pneumonia results from maternal infection of the newborn during vaginal delivery, and symptoms are exceedingly rare before the infant is a month old. Chlamydia produces a characteristic "staccato cough" and often conjunctivitis. It is radiographically dramatic, with hyperaeration and numerous, variously shaped interstitial densities scattered evenly throughout the lungs.
Viral pneumonia is rare in newborns.
* Group B streptococcal infection. Group B streptococci (GBS) infections are passed from mother to infant before, during or soon after birth. More than a quarter of American women are infected with this organism when giving birth.
While early presentation (1 to 5 days after birth) is typically a respiratory infection, late presentation (5 to 28 days after birth) usually is due to bacterial invasion of the newborn brain (meningitis). Sepsis due to severe GBS infection often is lethal. Chest radiographs of GBS exhibit a range of signs, from diffuse granularity that is more coarse than in RDS (but nevertheless sometimes mistaken for it), to right pleural effusions that are larger than left-side effusions. (See Fig. 6.)
* Tuberculosis. Tuberculosis (TB) is increasing in frequency, particularly in major urban areas with frequent immigration from tropical countries and eastern Europe. Inflammatory exudates in the lungs cause localized airspace disease. TB spreads from peripheral airspaces to central lymph nodes, and after several weeks, localized necrosis may be seen. AP radiographic examination is necessary for early detection and diagnosis.
* Transient tachypnea of the neonate (TTN). TTN results from abnormal delays in the transition from fetal lung physiology to extrauterine function8 and is most often seen among caesarean section-delivered newborns whose mothers did not experience labor. It is usually a disorder corrected by the infant's own body within 2 days of birth.
During prenatal development, an infant's lungs contain amniotic fluid. At delivery, the lungs are reprogrammed to absorb fluid and breathe air. This reprogramming does not occur in TTN. Although respiratory distress associated with TTN is usually moderate, pulmonary fluid interferes with gas exchange and can result in persistent pulmonary hypertension.
TTN often is identified radiographically by retained lung fluid resulting in pulmonary fissures. The lungs also appear to be mildly overexpanded and hazy.8
* Pulmonary hemorrhage. Neonatal pulmonary hemorrhage is evidenced clinically by bleeding from the mouth or trachea and respiratory insufficiency. Complete cardiovascular collapse may accompany major blood loss. Chest radiographs reveal a bilateral "white-out" sign due to increased densities. (See Fig. 7.)
Traditional chest radiography remains an important diagnostic tool in neonatal cardiovascular imaging, but color Doppler ultrasound, CT and MR have become critical for identifying some cardiovascular abnormalities.
* Congenital heart disease. Congenital heart disease (CHD) involves a number of distinct abnormalities that can be classified as either cyanotic or acyanotic.
Low levels of oxygen perfusion into blood cause cyanosis, a discoloration of the infant's lips, fingers and toes that can vary from gray to purplish blue. Cyanotic congenital heart lesions are of 3 types:
1. Oligemia. Insufficient blood reaches the oxygen-delivering pulmonary alveoli cells due to reduced pulmonary vascularity. Examples include double outlet ventricles and tetralogy of Fallot (see below).
2. Intracardiac mixing. Insufficiently oxygenated blood reaches the rest of the body because oxygenated, arterial blood and deoxygenated, venous blood are mixing in the heart.
3. Plethora. Despite increased pulmonary vasculature, markedly reduced pulmonary perfusion results in insufficiently oxygenated blood reaching the rest of the body. Examples include transposition of the large arteries and single ventricle.
Acyanotic lesions usually involve shunt or septal defects or cardiac failure due to lesions of the aorta.
CHD often presents with symptoms very similar to those seen in RDS. Infants who fail to improve after treatment with exogenous surfactant should be fully examined for heart defects. Chest radiography and electrocardiogram examinations are indicated in such cases.
Radiographic examination can help clinicians differentiate between oligemia-related cyanotic CHD and plethora-related cyanotic CHD. The decreased pulmonary vascularity of oligemia-related lesions, for example, presents radiographically as thorax-filling, "lucent" lungs on chest radiographs (ie, the lungs appear black and without normal radiographic visibility of vasculature). Plethora, on the other hand, involves increased demonstration of lung vasculature.
One of the most common cyanotic congenital heart diseases in infants is tetralogy of Fallot. Tetralogy of Fallot is caused by 4 morphological defects that result in insufficient oxygenation of the neonatal blood supply. It presents radiographically as oligemic lungs. The morphological defects underlying the disease are:
1. Ventricular septal defect (ie, a hole between the right and left ventricles).
2. Displaced aorta.
3. Thickened right ventricle wall.
4. Narrowing of the pulmonary valve.
These defects cause unoxygenated blood to dilute oxygenated arterial blood in general circulation and decrease blood flow to the lungs. Tetralogy of Fallot rarely presents with symptoms at birth, but in the weeks and months after birth vigorous crying or feeding may result in cyanosis. These episodes are known as "Tet spells."
Various stressors encountered during prenatal gestation, including viral infection, maternal alcohol consumption and malnutrition, seem to contribute to this disease. Women older than 40 years of age and those who have diabetes also are at increased risk of having children with tetralogy of Fallot, and the disease is more common in children with Down syndrome. Clinical symptoms include shortness of breath and cyanosis. Surgical correction of cardiac defects usually is performed when the child is 3 to 5 years old.
Radiographically, tetralogy of Fallot exhibits oligemic lungs and an upturned cardiac apex that appears to "float" above the diaphragm. (See Fig. 8.)
Disorders of the Brain
In addition to ultrasound, CT and MR are favored techniques for many neurological imaging applications because several commonly suspected disorders (eg, hydrocephalus) can be definitively diagnosed solely from a cross-sectional image of the brain.
The neonatal skull varies from adult norms in terms of bone thickness, sutures and the size of the facial skeleton relative to the brain. Normal features of the infant skull commonly are mistaken for abnormalities. The infant skull is not yet a contiguous bone surface, for example, but a set of incompletely sutured plates. Sutures commonly are mistaken for fractures.
In general, the first-line technique for imaging suspected intracranial hemorrhage is ultrasound, whereas CT and, in some cases, MR are indicated for brain trauma and asphyxia. In most cases, initial imaging with ultrasound is advisable, with follow-up examinations using more precise imaging techniques. Diagnosis and assessment of major neurodevelopmental disorders require the anatomical detail provided by MR.
* Intraventricular hemorrhage. Intraventricular hemorrhage (IVH) is common among premature neonates between gestational ages 24 and 30 weeks. About 80% of the time, IVH occurs within 72 hours of delivery, and many hospitals routinely examine preterm infants' brains using ultrasound by the end of the first week after delivery to screen for IVH.
The vasculature of preterm infants' brains is particularly vulnerable to hemorrhage, including a vascular structure known as the choroid plexus, which is not found in term infants' brains. Most IVH in preterm infants results from the failure of this anomalous vasculature. Cases of IVH are graded according to location and amount of bleeding. Grades 1 and 2 refer to small IVH that are unlikely to generate clinical symptoms and probably would not be identified without routine brain ultrasound. Grade 3 refers to a large IVH and dilatation or enlargement of the hollow ventricles that contain cerebrospinal fluid. Grade 4 IVH involves major damage to the brain parenchyma and seizure risk. Grade 4 IVH appears on ultrasound as large echogenic areas along the ventricles, which appear black.
Multiple or severe (Grade 3 or 4) hemorrhages can result in posthemorrhage hydrocephalus, seen in coronal ultrasound examinations as dramatic dilatation of the ventricles. (See Figs. 9 and 10.)
* Cerebral infarction. Neonatal stroke has many causes, including maternal cocaine use, extreme and sudden head and neck motion, embolism caused by fragments of placenta, cyanotic CHD and meningitis. Seizures within 3 days after delivery indicate a localized cerebral infarction involving the middle cerebral artery. Ultrasound results can suggest infarction, but CT offers more definitive confirmation. (See Fig. 11.)
* Hydrocephalus. Congenital hydrocephalus (from the Greek for "water on the head") is associated with numerous neurodevelopmental disruptions and abnormalities, such as Alpert's disease (a craniofacial dysmorphism), Dandy-Walker malformation (gross enlargement of the brain's fourth ventricle), tumors, toxoplasmosis or other intrauterine infection-caused hemorrhages and vascular malformations.
Marked cranial enlargement, often with splaying of the sutures, and raised intracranial pressure are clinical signs in most cases of neonatal hydrocephalus, regardless of cause. In ultrasound examinations, brain ventricles often are enlarged and, in severe cases, the brain tissue immediately around the ventricles shows edema.
* Encephalitis. Encephalitis is a brain inflammation resulting from viral infection. Herpes simplex virus type 1 (HSV1) encephalitis is the most common form of encephalitis. MR more sensitively detects HSV1 than CT, but both techniques can yield false negative or inconclusive results early in infection.
The neonatal skull contains 7 cranial plates, joined incompletely by sutures that have yet to close and ossify. Radiologic technologists should recognize normal skull sutures to avoid mistaking them for fractures. (See Fig. 12.)
Where sutures do not yet meet, fontanelle membranes are found. These membranes allow for skull growth during the first year of life. The 2 major fontanelles are the anterior fontanelle (the "soft spot") at the top of the infant's head and the posterior fontanelle in the center back of the head. Dehydration can cause the fontanelles to become "sunken" or depressed, as can malnutrition or insipient diabetes. The posterior fontanelle normally closes and begins to ossify by 2 months of age, and the anterior fontanelle closes by age 2 years. Delayed closure of the fontanelles is associated with premature birth, hydrocephalus, Down syndrome and, less often, hypothyroidism or rickets.
* Craniosynostosis. Premature closure of the cranial sutures or craniosynostosis can result in clinically insignificant aesthetic problems or severe physical limitation of head and brain growth (microcephaly). Early radiological confirmation of suspected cases is critical because surgical correction is most successful if undertaken early in the disease process. CT and MR are the preferred imaging techniques for assessing probable cases of craniosynostosis because they allow detailed imaging of the skull and assessment of hydrocephalus, for which infants with craniosynostosis are at increased risk.
The 2 most common forms of craniosynostosis are sagittal and coronal. In sagittal craniosynostosis, the skull appears long and narrow, with coronal, metopic and lambdoid sutures clearly visible, but the sagittal suture closed into a fused, raised ridge. Coronal synostosis is marked by a flattened forehead and craniofacial abnormalities.
Other Skeletal Disorders
Most neonatal bone imaging examinations are the result of clinical evidence of trauma, infections or congenital abnormalities. Suspected bone infections, such as osteomyelitis (which is very rare in neonates) may indicate scintigraphic examination, but in most cases, plain-film radiography is the imaging technique of first resort when neonatal bone disorders are suspected. Bone scintigraphy is not as diagnostically precise in newborns as in older children or adults, mainly because neonatal bone is still maturing, and this metabolic activity can interfere with radiopharmaceutical uptake. Ultrasound is indicated for assessment of suspected hip dysplasia or spinal injuries. MR and CT play minor roles in diagnostic imaging of the neonatal skeleton.
Growth abnormalities (skeletal dysplasias) are a major class of neonatal pathology, with more than a hundred dysplastic disorders described in the medical literature.
* Hypoplasia. The absence (aplasia) or retarded growth (hypoplasia) of bones of the extremities is called "phocomelia." Birth defects related to prenatal maternal use of the drug thalidomide, formerly prescribed to control morning sickness, are a classic example of phocornelia. Prenatal viral infection or genetic mutations also may cause this developmental skeletal disorder. The femur and radius are most often involved. Radiologically, hypoplastic bones commonly exhibit bowing and unusually thick bone cortex on the inner side of the curvature.
* Thanatophoric dysplasia. The most common of the deadly bone dysplasias is thanatophoric dysplasia. Retarded lung development results in death shortly after birth in most cases. Whole-body radiographic examination reveals a head of normal size but a small body with shortened limbs.
* Osteogenesis imperfecta. Clinically, osteogenesis imperfecta presents as unusually fracture-prone bones with thin long-bone cortices. As with thanatophoric dysplasia, neonates who are not stillborn die soon after delivery because of catastrophically underdeveloped lung physiology. Radiographs reveal numerous fractures, particularly in the long bones, which may be mistaken for severe child abuse or other trauma.
* Osteopetrosis. Proper bone development involves bone building on the outer bone by osteoblast cells and bone resorption and remodeling of the inner bone by osteoclast cells. Remodeling allows healthy bones to respond to recurrent forces by strengthening stressed bone tissue. Osteopetrosis is an osteoclast disorder in which bone is not remodeled. This typically results in fracture-prone, thick bones that often exhibit the "bone within bone" sign. This sign is particularly common in femurs. Clinically, osteopetrosis causes infant failure to thrive and anemia.
* Congenital dysplasia of the hip. Congenital hip dislocation (CDH) can result from breech births or prenatal disruption of hip bone development. For reasons that remain unclear, girls are affected at a rate some 500% higher than seen among boys. The primary clinical sign of CDH is a neonate's dislocated or dislocatable hip. Ultrasound examination of CDH reveals abnormalities in femoral head orientation.
* Septic arthritis. Streptococcus, Staphylococcus or Haemophilus influenzae bacteria infecting the hip or knee can result in painful, localized pseudoparalysis. Clinically, sepsis and warm, localized inflammation are the primary clues of septic arthritis. White blood cell counts are elevated. Radiographs initially may appear normal, but sequential images taken over the course of a week reveal the emergence of radiolucencies in the affected bone and increasing soft-tissue swelling around the hip or knee joints.
Traditional plain-film radiography remains the technique of choice in gastrointestinal (GI) imaging. Swaddling with a warm blanket and pacification with glucose usually is sufficient for GI radiography. Ultrasound is indicated when there is clinical evidence of liver, spleen or pancreatic inflammation. However, because many neonatal abdominal symptoms are vague and unlocalized, radiography usually is employed before ultrasound. For a suspected abdominal tumor or abscess, CT is used as a follow-up examination when radiography and ultrasound yield diagnostically insufficient imaging. CT exams of the neonatal GI tract are undertaken with careful attention to exposing only the target tissues or organs to radiation. For blunt abdominal trauma, CT is the imaging technique of first resort.
When CT or radiographic contrast is required for GI imaging, swallowed barium is typically the contrast agent of preference because it is physiologically inert and inexpensive. However, barium contrast can form solid clumps above bowel obstructions.[8 In cases of bowel perforation, barium contrast can infiltrate the peritoneal cavity. If it creates peritoneal granulomas, surgical removal may be necessary. For these reasons, water-soluble contrasts often are used instead, though aspiration is still a danger with any GI-tract contrast administered to the newborn. Intestinal air also serves as a contrast agent.
* Acute abdomen. Acute abdominal distress is best explored by obtaining a supine AP radiograph and a cross-table lateral radiograph of the prone infant. In these examinations, intestinal air serves as a contrast medium. In the supine position, air fills and makes visible small bowel loops and the colon. In prone exams, the air moves into the more posterior small bowel loops (areas of the colon not visualized in supine exams) and the rectum. Small bowel obstructions are detected on the prone radiographs.
* GI obstruction. Clinical symptoms often are indicative of the location (level) of GI atresia (obstruction). Esophageal obstructions prevent feeding and result in an inability to pass nasogastric tubes into the stomach. Bowel obstruction above the ampulla of Vater (ie, where the bile duct and pancreatic duct drain into the duodenum) causes nonbilious vomiting, whereas bowel obstruction proximally below the ampulla of Vater causes bilious vomiting. (Green vomit is a strong sign of GI.obstruction.) Lower bowel obstructions cause abdominal distension and later, bilious vomiting and dehydration.
Chest and abdominal radiographs are required to detect esophageal atresia. Inability to pass nasogastric tubes into the stomach often is demonstrated radiographically as the nasogastric tube turning back on itself at the site of obstruction.
Radiography of lower GI obstruction reveals dilated abdominal loops and bowel distention. Because the newborn's haustral folds are poorly developed, it is not possible to distinguish the small and large bowels on most radiographs. This can be corrected by administering a water-soluble lower-GI contrast.
Anal atresia (imperforate anus) may be due to prenatal developmental disruptions resulting in the misplacement or absence of the neonatal anus. Surgical correction requires radiologic identification of the location of the bowel terminus. A prone lateral cross-table projection of the pelvis accomplishes this well, as does the horizontal beam lateral projection radiograph of the abdomen with the infant held suspended upside down. AP films can reveal associated malformations of the bowel.
* H-type tracheo-esophageal fistula (TOF). This condition causes recurring pneumonia because food is passed into the airways during feeding through a fistula, an anomalous connection between the trachea and esophagus. High-pitched, noisy respiration (stridor) is sometimes the only symptom, and this disorder often is mistaken for an esophageal obstruction or swallowing discoordination problem. Radiographically, the H-type TOF appears as a "kissing" of upper trachea and esophagus, with the space between them disappearing as they bulge inward toward one another. Rigid bronchoscopy or the prone lateral pull-back esophagogram offer more definitive evidence of H-type TOF. The hazard of the latter exam is that contrast can be aspirated via the fistula, causing respiratory distress. A team of experienced radiologists and clinicians always should be present for this procedure.
* Bowel perforation and necrotizing enterocolitis. Free air in the peritoneal cavity (pneumoperitoneum) suggests perforation of the GI tract, particularly if the patient has not had a recent abdominal surgery. Neonatal pneumoperitoneum most often is due to necrotizing enterocolitis (NEC), particularly among preterm infants, but also may be a result of other disorders, such as distal bowel obstructions or thermometer-caused perforation of the newborn's rectum. Bowel perforation is a surgical emergency, and radiologic assessment is best achieved with a supine abdominal radiograph. Suspected NEC indicates sequential radiographic examinations, with supine abdominal films obtained every 12 or 24 hours. Radiological signs of NEC commonly include diffuse gaseous distention of the intestine. (See Fig. 13.)
Renal imaging is indicated by several well-defined signs. These include oliguria, renal failure, palpable renal masses, hypertension and poor urine stream. Oliguria is defined as less than 1 mL/kg body mass per hour of urine flow after the first day postdelivery.
Due to physiological immaturity (eg, a lower filtration rate than with older children), renal contrast imaging historically has been an unusually difficult and frustrating endeavor. Now, however, ultrasound is used to identify major renal structural abnormalities, such as marked hypoplasia or the absence of kidneys. In addition, renal scintigraphic scans are used to obtain information about kidney function when clinical data, such as urine flow rate and electrolyte content, are inconclusive.
Because renal flow scintigraphy involves use of the radiopharmaceutical tracer diethylenetriamine pentaacetic acid (DTPA) labeled with the radioactive isotope technetium Tc 99m, renal scans should be undertaken only when symptoms persist but clinical functional data are inconclusive. Normal kidneys pass the tracer quickly and scans are light; decreased function results in lingering radiopharmaceutical in the affected kidney and a dark renal scan.
* Renal failure. Renal failure may be due to many factors, from the absence of kidneys to renal obstruction. Radiologic technologists working with newborns should be familiar with 2 causes in particular: asphyxial renal trauma and renal venous thrombosis.
Perinatal asphyxia can cause brain damage and multiorgan failure, including necrotizing enterocolitis and renal failure. Neonatal renal failure due to asphyxia commonly is associated with birth trauma. If renal trauma is self-limited, resolution can occur spontaneously. In more severe cases, however, renal cortical necrosis (death of the kidneys' outer cells) occurs, leading to a range of outcomes, from death to incomplete recovery of renal function.
Radiologic assessment of asphyxia-related renal failure is performed with ultrasound. Asphyxia increases the echogenicity of the outer (cortical) kidneys, the renal medulla (inner kidneys) or both. Increased echogenicity of damaged renal tissue results in a "bright kidney" sign, which is particularly apparent when one kidney is damaged more than the other. Often, differentiation of the normally dark or low-echogenic renal cortex from the more echogenic renal medulla is lost due to damage in both sites.
Renal vein thrombosis results from dehydration, asphyxia, umbilical vein catheterization and sepsis. The lower half of the body often is swollen. Umbilical vascular catheters are a risk factor for renal vein thrombosis. Ultrasound reveals a smooth, enlarged kidney. As with asphyxia-related renal necrosis, renal vein thrombosis often results in a loss of echogenic differentiation between the kidney cortex and medulla. Doppler ultrasound reveals decreased venous blood flow from the affected kidney.
* Polycystic kidney. Renal mass and renal failure within a month of birth are clinical signs of polycystic kidney disease. Infantile (or "autosomal recessive") polycystic kidney disease is different than adult polycystic kidney disease, though the latter can, rarely, occur in infants. Infantile polycystic kidneys develop a pathological overabundance of renal collecting tubules, causing the formation of numerous cysts from 1 to 2 mm in diameter. Lesions often are seen in the liver, as well. Oversized, echogenic kidneys are visible on ultrasound examination.
Premature infants often require radiographic examination to ensure proper placement of tubes and lines, such as IV lines, endotracheal tubes and nasogastric drainage tubes. Clinically, endotracheal tube placement problems are evidenced by unusual breathing sounds and insufficient oxygen saturation of the blood. Improper head positioning during endotracheal tube insertion (such as tube insertion while the infant's head is flexed) will almost always result in improper tube position. A common endotracheal tube placement error that is readily detected by radiographic examination is tube overextension into the bronchus. This results in one lung being poorly ventilated and, sometimes, air trapping and overdistension in the other lung.
Advances in neonatal imaging applications are rapidly providing pediatric imaging units with more precise, more sensitive diagnostic tools. Though radiography remains a primary imaging technique in this field, others play an increasingly important role in imaging the newborn.
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Bryant Furlow, B.A., studied biology at the University of New Mexico in Albuquerque, graduating with top honors. He is now a freelance science and medical writer living in California.
Reprint requests may be sent to the American Society of Radiologic Technologists, Communications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3917.
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