Practice Essentials
Transient tachypnea of the newborn (TTN) appears soon after birth and has been identified as occurring with cesarean birth and infant sedation. [1, 2, 3, 4, 5] It may be accompanied by chest retractions, expiratory grunting, or cyanosis, which can be relieved with minimal oxygen. Recovery is usually complete within 3 days. [6, 7] Studies have shown that TTN can account for 33-50% of breathing difficulties in neonates. [8, 9, 10]
Radiologically, this syndrome frequently is termed wet lung disease. In the medical literature, discussions concerning transient tachypnea of the newborn can also be found under the following names: retained fetal lung liquid, retention of fetal lung fluid, respiratory distress syndrome type II, transient respiratory distress of the newborn, and neonatal retained fluid syndrome.
The lungs usually are affected diffusely and symmetrically, and the condition is commonly accompanied by a small pleural effusion. [11, 12] The clinical course of transient tachypnea is relatively benign when compared with the severity suggested by chest films. Radiographic resolution by the second or third day characterizes this entity and differentiates it from other possible disorders; if radiographic resolution is not complete by the third day or if respiratory symptoms persist longer than 5 days, an alternative diagnosis should be sought.
A correlation between coronavirus disease 2019 (COVID-19) exposure and TTN has been reported. A study comparing 101 infants born to a COVID-19-positive mother and 101 infants born prior to the start of the pandemic found the risk of development of TTN was 3 times higher in the COVID-19 group (OR= 3.270, 95% CI: 1.017-10.512). TTN was also the most common diagnosis among the infants of COVID-19 mothers across all modes of delivery. [13]
(See the images below.)
Chest radiograph of a neonate at age 2 days. Moderate parenchymal abnormalities with perihilar, streaky markings. No cardiomegaly.
Radiograph of a neonate at age 4 days. Normal heart size and clear lungs are seen.
Standard chest radiography is the preferred radiologic examination. Initially, it may be difficult to distinguish transient tachypnea from other causes of respiratory distress of the newborn.
Raimondi et al studied 65 patients with TTN and found that 31 (47.6%) had the double lung point sign (sharp echogenicity increase in the lower lung fields) on ultrasonography. They also found that a regular pleural line with no consolidation is a consistent finding in TTN and that the presence of a double lung point is not essential for the ultrasound diagnosis of TTN. [14]
Ultrasonography allows relatively easy differentiation between hyaline membrane disease, transient tachypnea of the newborn, and neonatal pneumonia. [15, 16, 17]
According to the POCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC), point-of-care ultrasound s helpful in distinguishing between respiratory distress syndrome (RDS) and transient tachypnoea of the neonate (TTN). RDS is characterized by a poorly aerated lung, with the absence of A-lines, the presence of small subpleural consolidations, and diffuse white lung (confluent B-lines). In TTN, however, the interstitial pattern alternates with areas of near-normal lung (with A-lines). [18]
The differential diagnosis includes Hyaline Membrane Disease, Meconium Aspiration, and neonatal pneumonia. Other conditions to be considered include respiratory distress syndrome, congenital lymphangiectasia, congenital heart disease, polycythemia, cerebral hyperventilation, and anemia/hypovolemia.
Differentiation from other causes of neonatal respiratory distress may take time. Initial evaluation, monitoring, and basic supportive care must cover all diagnostic contingencies.
Overall prognosis is excellent, with most symptoms resolving within 48 hours. Malignant TTN has been reported in some cases, in which newborns develop persistent pulmonary hypertension because of a possible elevation of pulmonary vascular resistance that is due to retained lung fluid. [19, 20, 21]
Radiography
Findings of transient tachypnea of the newborn (TTN) on chest radiographs may include mild, symmetrical lung overaeration; prominent perihilar interstitial markings; and small pleural effusions (see the first image below). [7, 11, 12, 22, 23] Occasionally, the right side may appear more opacified than the left.
The radiographic appearance at times can mimic the diffuse, granular appearance of hyaline membrane disease but without pulmonary underaeration. Neonates with transient tachypnea are usually at term. Radiographic lung changes also may resemble the coarse, interstitial pattern of other causes of pulmonary edema or the irregular pattern of lung opacification seen in meconium aspiration syndrome.
The degree of confidence is rather low. Clinicoradiologic correlation helps confirm the diagnosis. Timing is also a key diagnostic factor.
Radiograph of a neonate at age 6 hours. Overaeration, streaky, bilateral, pulmonary interstitial opacities and prominent perihilar interstitial markings. Mild cardiomegaly.
Chest radiograph of a neonate at age 2 days. Moderate parenchymal abnormalities with perihilar, streaky markings. No cardiomegaly.
Radiograph of a neonate at age 4 days. Normal heart size and clear lungs are seen.
Ultrasonography
A persistent radiographic finding of cardiomegaly should raise suspicions of congenital heart disease. Evaluation by a pediatric cardiologist and echocardiographic imaging should follow. Ultrasound also permits relatively easy differentiation between hyaline membrane disease, transient tachypnea of the newborn, and neonatal pneumonia. Ultrasound studies have been performed for transient tachypnea of the newborn. Lung ultrasound has become an attractive diagnostic tool in neonatal settings and is used for diagnosing several neonatal respiratory morbidities. It has been proposed for helping predict interventions such as NICU admission and surfactant treatment or mechanical ventilation in preterm infants. [24, 15, 25, 26, 27, 28, 29, 30, 18, 14]
In a study comparing 32 newborn infants with radiologic and clinical findings of transient tachypnea of the newborn, a sonographic image called the “double lung point” was described, with the authors reporting a sensitivity and specificity of 100% for the diagnosis of TTN when compared to 60 healthy normal infants—29 with respiratory distress syndrome, 6 with pneumonia, and 5 with atelectasis. [28] Further studies of this sign have found a sensitivity that ranges from 38% up to 100%, [31] with specificities close to 100%. [32] .
In a lung ultrasound, B lines are defined as "comet tail" artifacts arising from the pleural line. [15] The interface between very compact B lines in the inferior pulmonary field, when compared to less compact B lines in the superior lung field, is what is known as as the double lung point. [32] Technical and anatomic concerns are more likely to be raised when ultrasound is used, and negative ethical and medicolegal implications become a matter of concern. [33]
Raimondi et al studied 65 patients with TTN and found that 31 (47.6%) had the double lung point sign (sharp echogenicity increase in the lower lung fields) on ultrasonography. They also found that a regular pleural line with no consolidation is a consistent finding in TTN and that the presence of a double lung point is not essential for the ultrasound diagnosis of TTN. [19]
Ultrasonography may be helpful in differentiating COVID-19 from TTN. In a study of 27 infants, the lung sonograms in 2 asymptomatic COVID-19-positive neonates revealed several coalescent B lines, pleural thickening, and areas of opacity. [34]
According to ESPNIC, point-of-care ultrasound s helpful in distinguishing between respiratory distress syndrome and transient tachypnoea of the neonate. [18]
At this point, ultrasound is not expected to substitute for radiography, and clinicoradiologic correlation is fundamental.
-
Radiograph of a neonate at age 6 hours. Overaeration, streaky, bilateral, pulmonary interstitial opacities and prominent perihilar interstitial markings. Mild cardiomegaly.
-
Chest radiograph of a neonate at age 2 days. Moderate parenchymal abnormalities with perihilar, streaky markings. No cardiomegaly.
-
Radiograph of a neonate at age 4 days. Normal heart size and clear lungs are seen.
