Respiratory Distress Syndrome Imaging
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Respiratory distress syndrome (RDS) of the newborn is an acute lung disease caused by surfactant deficiency, which leads to alveolar collapse and noncompliant lungs. Previously known as hyaline membrane disease, this condition is primarily seen in premature infants younger than 32 weeks’ gestation.
RDS is usually diagnosed with a combination of clinical signs and/or symptoms, chest radiographic findings, and arterial blood gas results. The radiographic features of RDS are seen in the images below. A normal film at 6 hours of life excludes the diagnosis of RDS.
The incidence and severity of RDS are inversely related to gestational age. RDS is the most common cause of respiratory failure during the first days after birth. In addition to prematurity, other factors contributing to the development of RDS are maternal diabetes, cesarean delivery without preceding labor, [1] being the second born of twins, perinatal asphyxia, perinatal infection, and patent ductus arteriosus. [2, 3, 4]
Complications of RDS are numerous, both acute and chronic. [5] Infants with RDS are at risk of developing alveolar rupture and pulmonary interstitial emphysema, infection, intracranial hemorrhage, chronic lung disease (bronchopulmonary dysplasia), retinopathy of prematurity, neurologic impairment, and sudden death.
The outcome of patients with RDS has improved with the increased use of antenatal steroids to improve pulmonary maturity, early postnatal surfactant therapy to replace surfactant deficiency, and gentle techniques of ventilation to reduce barotrauma to the immature lungs.
A Cochrane meta-analysis showed that antenatal corticosteroid therapy to women at risk of preterm delivery reduces the incidence of RDS, neonatal death, and intraventricular hemorrhage. [6]
Recent meta-analyses have confirmed that exogenous surfactant treatment decreases overall morbidity and mortality in preterm newborns with RDS. A study by Soll et al demonstrated that multiple doses of animal-derived surfactant extract provided greater improvement than single-dose therapy with regard to oxygenation and ventilatory requirements, reduced risk of pneumothorax, and improved survival. [5] Efforts are ongoing to identify the optimal delivery method and dosages. [4]
Central positive airway pressure (CPAP) is used as an adjunct therapy given after surfactant therapy and helps to prevent atelectasis and apnea.
Lahra et al found that maternal and fetal intrauterine inflammatory responses (chorioamnionitis and umbilical vasculitis) are protective for RDS. In this study, chorioamnionitis with umbilical vasculitis was found to provide a markedly greater reduction of RDS than the presence of chorioamnionitis alone. [7]
In respiratory distress syndrome (RDS), the classic chest radiographic findings consist of pronounced hypoaeration, bilateral fine granular opacities in the pulmonary parenchyma, and peripherally extending air bronchograms.
The radiologic spectrum of RDS ranges from mild to severe and is generally correlated with the severity of the clinical findings. In the early stages of the disease, notable air bronchograms are lacking, because the major bronchi lie in the more anterior portions of the lungs and because alveolar atelectasis tends to involve the dependent areas of the lungs, which are posterior in recumbent infants. However, a bubble appearance, which represents overdistended bronchioles and alveolar ducts, can be observed. See the image below.
The appearance of granular opacities is to the result of superimposition of multiple acinar nodules caused by atelectatic alveoli and interstitial fluid. The development of air bronchograms depends on the coalescence of areas of acinar atelectasis around aerated bronchi and bronchioles. In nonintubated infants, cephalic doming of the diaphragms and hypoaeration are observed.
In infants with mild-to-moderate RDS, hypoaeration and fine granular opacities persist for 3-5 days following the administration of surfactant. Clearing from the peripheral to the central areas and from the upper lobe to the lower lobe begins at the end of the first week. See the image below.
As RDS progresses, the reticulogranular pattern becomes prominent due to coalescence of the small atelectatic areas. This coalescence leads to larger areas of increased lung opacity. As the anterior portions of the lung become involved with microatelectasis, the granularity becomes uniformly distributed, and air bronchograms can be seen. See the image below.
With increasing severity of disease and worsening hypoaeration, progressive opacification of the anterior portions of the lungs cause obscuration of the cardiac silhouette and the formation of prominent air bronchograms. With severe disease, the lungs appear opaque and display prominent air bronchograms, with total obscuration of the cardiomediastinal silhouette. This type of severe and progressive RDS often leads to death, usually within 72 hours.
The radiographic findings of RDS depend on the timing of the administration of surfactant.
Because the surfactant is not evenly distributed throughout the lungs, areas of improving lung alternating with areas of unchanged RDS is common. This uneven distribution leads to a radiographic appearance similar to that of other entities, such as neonatal pneumonia and meconium aspiration syndrome. The clearing is sometimes irregular, creating a cystic appearance. Relapse may occur after initial improvement.
Infants who are being ventilated with intermittent positive pressure with positive end-expiratory pressure may have well-aerated lungs without air bronchograms. Infants with severe disease may be unable to expand their lungs; they have total opaque radiographs.
Because infants with RDS are usually hypoxic, the ductus arteriosus may remain patent. Early in the disease, shunting is from right to left. By the end of first week, shunting becomes left to right as pulmonary artery pressure decreases because of the increased compliance of the healing lungs. Interstitial pulmonary edema may develop. Therefore, when the granular pattern of hyaline membrane disease changes to a homogeneously opaque appearance, pulmonary edema due to patent ductus arteriosus (or early chronic pulmonary changes should be suspected.
Early
With positive-pressure ventilation, the lungs’ opacity decreases, and they appear radiographically improved. However, the positive pressure required to aerate the lungs can disrupt the epithelium, producing interstitial and alveolar edema. It can also cause the dissection of air into the interlobar septae and their lymphatics, producing pulmonary interstitial emphysema (PIE), which has the appearance of tortuous, 1- to 4-mm linear lucencies that are relatively uniform in size. These radiate outward from the hilar regions. The lucencies do not empty on expiration and extend to the periphery of the lungs. PIE is shown in the image below.
PIE can be symmetrical, asymmetrical, or localized to one portion of a lung. Peripheral PIE can produce subpleural blebs and ultimately rupture into pleural space to produce pneumothorax (usually tension pneumothorax, shown in the image below), or they can extend centrally to produce pneumomediastinum or pneumopericardium. Because infants are supine and because air rises to the highest point of the thorax, the pneumothorax is located paramediastinally, resulting in the sharp mediastinum sign, whereby the mediastinum/heart is sharply outlined by adjacent free air rather than aerated lung tissue.
A continuous diaphragm sign, which is caused by air in the mediastinum beneath the heart, may be seen with pneumomediastinum. When alveoli rupture, air may become localized and may coalesce in the parenchyma to produce pulmonary pseudocyst. In addition to parenchymal pseudocysts and PIE, alveolar rupture may allow air to enter the pulmonary venous system, leading to systemic air embolism with intravascular air.
Late
Late in the course of the disease, pulmonary edema, air leaks, or pulmonary hemorrhage can affect the radiographic appearance.
Meconium aspiration syndrome (shown below) usually occurs in postterm infants, especially in those with meconium staining. Clinical symptoms usually appear 12-24 hours after birth. (In contrast, clinical symptoms of RDS always appear within the first few hours of life.)
The most common radiographic features are hyperaeration and bilateral, diffuse, and grossly patchy areas of increased radiopacity. Pneumothorax in fetal aspiration syndrome is usually not tension pneumothorax; therefore, it often requires no specific therapy. In RDS, the lungs are hypoaerated, and the abnormal lung opacities due to atelectasis are finely granular. In addition, pneumothorax related to RDS is often under tension, and surgical intubation is required.
Transient tachypnea of the newborn (TTN), seen in the image below, usually occurs in term infants, usually after cesarean delivery. Clinical symptoms usually manifest within 6 hours of birth. Radiographic findings include increased or normal lung volume, with interstitial edema and pleural effusions. In RDS, bilateral reticular or granular parenchymal opacities are present for at least 3-4 days, whereas in transient tachypnea, these opacities are fleeting. Hypoaeration is typical of RDS, in contrast to the hyperaeration of transient tachypnea.
Neonatal pneumonia is usually associated with premature rupture of membranes. Clinical symptoms appear less than 6 hours after birth. Radiographic findings include perihilar streaking. Neonatal pneumonia often produces hyperaeration of the lungs, but in general, the areas of pneumonia are focal rather than diffuse. Pleural effusions may be the only distinguishing feature; they are not a feature of uncomplicated RDS but are present in as many as two thirds of patients with pneumonia. Group B beta-hemolytic streptococcal pneumonia often occurs with RDS, or it can mimic the appearance of RDS. Hence, many neonatal units give antibiotics to all neonates with this condition until blood cultures are negative.
Differentiating RDS from diffuse pulmonary hemorrhage may be difficult. One feature that aids in the differential diagnosis is the identification of a pleural effusion. Pleural effusions are rare in RDS but are common in pulmonary hemorrhage.
If chest images in a premature infant show reticulogranular opacities, RDS can be diagnosed with 90% confidence.
The use of lung ultrasound in diagnosing respiratory distress syndrome (RDS) has been very infrequent to date; however, a recent pilot study by Liu et al has suggested that it can be an accurate and reliable modality that is also rapid, portable, and nonionizing. [8]
Findings of lung consolidation, pleural-line abnormalities, lung pulse, bilateral “white lung” or alveolar interstitial syndrome, and A-line disappearance were found to be very sensitive and very specific when compared with conventional portable chest radiography. In addition, ultrasonography can be useful to diagnose or exclude a simultaneous or complicating pleural effusion. [9]
Bedside lung ultrasonography was found, in one study, to be superior to chest radiography in detecting consolidation and subpleural atelectasis, but not in detecting pneumothorax, in premature newborns with respiratory distress syndrome. Alveolo-interstitial syndrome and pleural line abnormalities were detected in all cases in the initial assessment, patchy consolidation was detected in 34 cases, and white lung was detected in 80 cases. [10]
In 23 infants with respiratory distress syndrome, lung ultrasound showed a sensitivity of 95.6%, specificity of 94.4%, positive predictive value of 91.6%, and negative predictive value of 97.1%. For transient tachypnea of the newborn in 30 infants, lung ultrasound showed a sensitivity of 93.3%, specificity of 96.5%, positive predictive value of 96.5%, and negative predictive value of 93.4%. [11]
Malloy MH. Impact of cesarean section on intermediate and late preterm births: United States, 2000-2003. Birth. 2009 Mar. 36(1):26-33. [Medline].
Ersch J, Roth-Kleiner M, Baeckert P, Bucher HU. Increasing incidence of respiratory distress in neonates. Acta Paediatr. 2007 Nov. 96(11):1577-81. [Medline].
Teksam O, Kale G. The effects of surfactant and antenatal corticosteroid treatment on the pulmonary pathology of preterm infants with respiratory distress syndrome. Pathol Res Pract. 2009. 205(1):35-41. [Medline].
Lopez E, Gascoin G, Flamant C, Merhi M, Tourneux P, Baud O. Exogenous surfactant therapy in 2013: what is next? Who, when and how should we treat newborn infants in the future?. BMC Pediatr. 2013 Oct 10. 13:165. [Medline]. [Full Text].
Soll R, Ozek E. Multiple versus single doses of exogenous surfactant for the prevention or treatment of neonatal respiratory distress syndrome. Cochrane Database Syst Rev. 2009 Jan 21. CD000141. [Medline].
Crowley P. Prophylactic corticosteroids for preterm birth. Cochrane Database Syst Rev. 2000. CD000065. [Medline].
Lahra MM, Beeby PJ, Jeffery HE. Maternal versus fetal inflammation and respiratory distress syndrome: a 10-year hospital cohort study. Arch Dis Child Fetal Neonatal Ed. 2009 Jan. 94(1):F13-6. [Medline].
Liu J, Cao HY, Liu Y. [Lung ultrasonography for the diagnosis of neonatal respiratory distress syndrome: a pilot study]. Zhonghua Er Ke Za Zhi. 2013 Mar. 51(3):205-10. [Medline].
Ahuja CK, Saxena AK, Sodhi KS, Kumar P, Khandelwal N. Role of transabdominal ultrasound of lung bases and follow-up in premature neonates with respiratory distress soon after birth. Indian J Radiol Imaging. 2012 Oct. 22(4):279-83. [Medline]. [Full Text].
Sawires HK, Abdel Ghany EA, Hussein NF, Seif HM. Use of lung ultrasound in detection of complications of respiratory distress syndrome. Ultrasound Med Biol. 2015 Sep. 41 (9):2319-25. [Medline].
Vergine M, Copetti R, Brusa G, Cattarossi L. Lung ultrasound accuracy in respiratory distress syndrome and transient tachypnea of the newborn. Neonatology. 2014. 106 (2):87-93. [Medline].
Avery GB, Fletcher MA, MacDonald MG. Acute respiratory disorders in neonatology. Pathophysiology and Management of the Newborn. 5th ed. Philadelphia, Pa: Lippincott; 1999. 485.
Patrick Do, MD Resident Physician, Department of Radiology, Santa Clara Valley Medical Center
Patrick Do, MD is a member of the following medical societies: Radiological Society of North America
Disclosure: Nothing to disclose.
Bo Yoon Ha, MD, MS Chief of Pediatric Radiology, Department of Radiology, Santa Clara Valley Medical Center
Bo Yoon Ha, MD, MS is a member of the following medical societies: American Society of Neuroradiology, Radiological Society of North America, Society for Pediatric Radiology
Disclosure: Nothing to disclose.
Mahesh R Patel, MD Chief of MRI, Department of Diagnostic Imaging, Santa Clara Valley Medical Center
Mahesh R Patel, MD is a member of the following medical societies: American Roentgen Ray Society, American Society of Neuroradiology, Radiological Society of North America
Disclosure: Nothing to disclose.
Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.
Kieran McHugh, MB, BCh Honorary Lecturer, The Institute of Child Health; Consultant Pediatric Radiologist, Department of Radiology, Great Ormond Street Hospital for Children, London, UK
Kieran McHugh, MB, BCh is a member of the following medical societies: American Roentgen Ray Society, Royal College of Radiologists
Disclosure: Nothing to disclose.
Eugene C Lin, MD Attending Radiologist, Teaching Coordinator for Cardiac Imaging, Radiology Residency Program, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine
Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, Society of Nuclear Medicine and Molecular Imaging
Disclosure: Nothing to disclose.
Beverly P Wood, MD, MSEd, PhD Professor Emerita of Radiology and Pediatrics, Division of Medical Education, Keck School of Medicine, University of Southern California; Professor of Radiology, Loma Linda University School of Medicine
Beverly P Wood, MD, MSEd, PhD is a member of the following medical societies: American Academy of Pediatrics, Association of University Radiologists, American Association for Women Radiologists, American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Radiological Society of North America, Society for Pediatric Radiology
Disclosure: Nothing to disclose.
Kathy Keller, MD, Chief, Department of Pediatric Radiology, Santa Clara Valley Medical Center
Disclosure: Nothing to disclose.
Thu T Le, MD Staff Physician, Department of Radiology, Santa Barbara Cottage Hospital
Disclosure: Nothing to disclose.
Peter C McClure, MD Staff Physician, Department of Radiology, San Francisco General Hospital
Disclosure: Nothing to disclose.
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