Respiratory distress syndrome (RDS) is a relatively common condition resulting from insufficient production of surfactant that occurs in preterm neonates.
On imaging, the condition generally presents as bilateral and relatively symmetric diffuse ground glass lungs with low volumes and a bell-shaped thorax.
RDS is also known as hyaline membrane disease (not favored as reflects non-specific histological findings), neonatal respiratory distress syndrome, lung disease of prematurity (both non-specific terms), or as some authors prefer surfactant-deficiency disorder 2.
The incidence is estimated at 6 per 1000 births 2. Uncommon after 36 weeks' gestation due to development of pneumocyte surfactant production around 35 weeks5.
Respiratory distress presents in the first few hours of life in a premature baby. Signs include tachypnea, expiratory grunting, and nasal flaring. The infant may or may not be cyanosed. Substernal and intercostal retractions may be evident.
Risk factors include maternal diabetes, greater prematurity, perinatal asphyxia and multiple gestations.
Associated abnormalities are those that can occur in prematurity: germinal matrix hemorrhage, necrotizing enterocolitis, patent ductus arteriosus, delayed developmental milestones, hypothermia and hypoglycemia.
Immature type II pneumocytes cannot produce surfactant. The lack of surfactant increases the surface tension in alveoli causing collapse. Patients have a decreased lecithin to sphingomyelin ratio. Damaged cells, necrotic cells, and mucus line the alveoli.
Although most cases are related to prematurity alone, rarely patients may have genetic disorders of surfactant production and can present in a similar clinical and radiological manner 6.
As the alveoli are collapsed (microscopically), the lungs are collapsed macroscopically as well. It is a diffuse type of adhesive atelectasis.
- low lung volumes is mandatory (atelectasis - lung collapse).
- diffuse granular opacities (ground glass), bilateral and symmetrical - "white lungs".
- air bronchograms may be evident.
- bell-shaped thorax.
- hyperinflation (in a non-ventilated patient) excludes the diagnosis; if the patient is intubated there might be hyperinflation.
RDS can be safely excluded if the neonate has a normal chest radiograph at six hours after birth.
If treated with surfactant therapy, there may be asymmetric improvement.
On transabdominal ultrasound, retrodiaphragmatic hyperechogenicity can be seen. If this hyperechogenicity does not resolves by day 9-18 on follow up ultrasound, it helps in prediction of risk of development of bronchopulmonary dysplasia.
Treatment and prognosis
Exogenous surfactant administration. Supportive oxygen therapy.
- persistent patent ductus arteriosus (PDA) due to reduced oxygen stimulus
- pulmonary interstitial emphysema (from treatment)
- oxygen toxicity (from treatment)
- pulmonary hemorrhage (can also be included in the differential diagnosis)
- air leak (barotrauma related to ventilation)
- 1. Blickman JG, Parker BR, Barnes PD. Pediatric radiology, the requisites. Mosby Inc. (2009) ISBN:0323031250. Read it at Google Books - Find it at Amazon
- 2. Agrons GA, Courtney SE, Stocker JT et-al. From the archives of the AFIP: Lung disease in premature neonates: radiologic-pathologic correlation. Radiographics. 25 (4): 1047-73. doi:10.1148/rg.254055019 - Pubmed citation
- 3. Donnelly LF, Frush DP. Localized radiolucent chest lesions in neonates: causes and differentiation. AJR Am J Roentgenol. 1999;172 (6): 1651-8. AJR Am J Roentgenol (citation) - Pubmed citation
- 4. Swischuk LE, John SD. Immature lung problems: can our nomenclature be more specific? AJR Am J Roentgenol. 1996;166 (4): 917-8. AJR Am J Roentgenol (abstract) - Pubmed citation
- 5. Liszewski MC, Lee EY. Neonatal Lung Disorders: Pattern Recognition Approach to Diagnosis. (2018) AJR. American journal of roentgenology. 210 (5): 964-975. doi:10.2214/AJR.17.19231 - Pubmed
- 6. Wert SE, Whitsett JA, Nogee LM. Genetic disorders of surfactant dysfunction. (2009) Pediatric and developmental pathology : the official journal of the Society for Pediatric Pathology and the Paediatric Pathology Society. 12 (4): 253-74. doi:10.2350/09-01-0586.1 - Pubmed
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