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Estimated Time for Completion: approximately 1 hour
Date of Release and Review: February 3, 2014, January 15, 2017
Expiration Date: January 31, 2020
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Embryologically, the diaphragm forms from: 1) the ventral portion of the septum transversum; 2) the dorsolateral portion from the pleuroperitoneal membranes; and 3) a medial dorsal portion. Diaphragmatic development is generally completed by the 9th week of gestation.
The defects associated with the diaphragm include: complete absence of the diaphragm; partial absence of the diaphragm (congenital diaphragmatic hernia); failure of muscularization (eventration); and congenital enlargement of the esophageal hiatus (hiatal hernia).
Bilateral agenesis of the diaphragm is a rare variant of congenital diaphragmatic hernia. Because of the pulmonary hypoplasia, these infants rarely survive1. Total absence of the hemidiaphragm has been reported once in a series of 143 cases of congenital diaphragmatic hernia2.
This is a rare defect with a complete absence of lung tissue and its associated arterial and venous infrastructure. It has been theorized that an early injury to the developing lung buds results in this congenital malformation. The absence of the lung allows the diaphragm and abdominal organs to be displaced cephalad, mimicking a congenital diaphragmatic hernia. The sonographic identification of the pulmonary veins entering the left atrium helps to exclude this diagnosis3.
With eventration, the failure of diaphragmatic muscularization permits the left or right hemi-diaphragm to ascend abnormally high in the chest. The eventration may be partial or complete. In the majority of cases, as with congenital diaphragmatic hernias, a diaphragmatic eventration is on the left side4.
Congenital pulmonary airway malformation (CPAM) and pulmonary sequestration may simulate or coexist with a congenital diaphragmatic hernia. An extralobar sequestration develops at 4 to 5 weeks’ gestation. Hence, an extrapulmonary sequestration may disturb fusion of the diaphragm. The position of an extrapulmonary sequestration may prevent herniation of the abdominal contents into the chest, permitting normal lung development. At the time of delivery, changes in intraabdominal pressure and breathing movements results in the extrusion of abdominal contents into the chest5.
This syndrome can be suspected when a congenital diaphragmatic hernia is associated with several of the additional stigmata outlined in Table I. Perinatal mortality is increased with Cornelia de Lange syndrome; survivors are developmentally delayed6,7,8.
Fryns syndrome has a constellation of congenital anomalies that would help to distinguish it from an isolated congenital diaphragmatic hernia (Table II). It has autosomal recessive inheritance. There is a high neonatal mortality due to the diaphragmatic hernia and secondary pulmonary hypoplasia9,10.
The incidence of congenital diaphragmatic hernia (CDH) is 1/2000 – 1/5000 livebirths11,12. If the fetuses with a congenital diaphragmatic hernia who have an in utero demise are included, i.e. the population of the sonologist, the incidence is closer to the 1/2000 figure13.
Embryologically, the pleuroperitoneal cavity closes and muscularizes by the time the small bowel returns from the umbilical cord to the abdomen at a menstrual age of 12 weeks14. As a result, bowel herniation into the chest occurs during the pseudoglandular (gestational age 5-16 weeks) phase of pulmonary development. Since the bronchial tree is forming, the presence of a chest mass results in a reduced number of bronchial divisions along with their associated alveoli. There is also a reduction in the vascular supply to, not only the ipsilateral lung, but also the contralateral lung. If the bowel contents slide intermittently between the abdominal and pleural cavity, the long-term effect upon lung development/function will not be as great.
The majority of CDH are posterolateral (Bochdalek’s hernia) in location and are on the left (Fig. 1)12. Approximately 15% are right-sided15.
Once a CDH is diagnosed, a careful extended fetal anatomic survey is mandatory. Associated congenital anomalies occur in 25% to 50% of CDH. As expected, the incidence of associated anomalies is increased even further in stillbirths with CDH16,17. Some of the more common associated anomalies are outlined in Table III16,18,19. Associated cardiac defects are the most frequent20; occurring in 16% of fetuses with CDH21 and account for 40% of anomalies associated with congenital diaphragmatic hernia15.
Chromosomal anomalies occur in 5– 34% of fetuses with CDH10,17,18,22,23. Trisomy 18 is the most common karyotypic abnormality23. A congenital diaphragmatic hernia is a characteristic finding with isochrome 12p (Pallister-Killian syndrome)23.
When an isolated CDH is diagnosed prior to 24 weeks’ gestation, the survival rate is approximately 40%24. If a defect is not detected during a 2nd trimester ultrasound examination, the survival with CDH is up to 100%25. The negative 2nd trimester ultrasound examination suggests that the defect is either small or that there is a sliding hernia that has less of an effect on pulmonary function26.
The prenatal detection rate of CDH varies between 29% and 100%27,28,29.
A sonographically detected increased nuchal translucency between 10 and 14 weeks’ gestation in fetuses who were subsequently found to have a congenital diaphragmatic hernia, is associated with a significant increase in neonatal death. It has been hypothesized that the larger congenital diaphragmatic hernias with lung compression impedes venous return, resulting the in lymphatic edema at the level of the head and neck30.
Table IV provides the sonographic findings associated with a congenital diaphragmatic hernia. The most common sonographic findings with CDH include: 1) a failure to visualize the fetal stomach in the abdomen (Fig. 2); 2) the fetal stomach in the chest (Fig. 3); and 3) fetal bowel within the chest (Fig. 1).
Some of the more recent sonographic findings with CDH include: 1) a horizontal stomach in the fetal abdomen with a right-sided CDH (Fig. 4)32; 2) a deviation of the umbilical vein toward the side of the defect in a transaxial view of the abdomen (Fig. 5)32; and 3) the observed/expected pulmonary artery diameters are significantly reduced in fetuses with CDH (Fig. 6)34,35.
On a parasagittal view of the chest and abdomen with fetal breathing, the abdominal contents enter the chest through a congenital diaphragmatic hernia. On the side with an intact diaphragm, the abdominal contents move in a normal downward direction31.
The liver and lung have a similar echogenicity. Color Doppler can be used to identify vessels extending from the intra-abdominal part of the liver into a herniated left or right lobe of the liver (Fig. 7)36.
The intra-thoracic abdominal organ herniation and rightward displacement of the heart with a left–sided CDH, results in preferential streaming of ductus venosus and inferior vena cava flow towards the right heart. As a result, the left heart is underdeveloped (Fig. 8)37. Although left heart dimensions may be below the normal range, these results do not affect postnatal outcome37.
In the presence of an isolated CDH, perinatal mortality is most closely associated with the severity of pulmonary hypoplasia. The right lung/fetal head circumference ratio (LHR) was originally proposed as a way to delineate the likelihood of survival with left–sided CDH38, 39. The maximum diameter of the right lung (in millimeters) are multiplied and divided by the head circumference (in millimeters). In the initial reports, a LHR ? 1.4 was associated with survival; all fetuses with an LHR < 1.0 died40.
A systemic review and meta–analysis of the standard lung-to-head ratio indicated that, as a prognostic tool in fetal CHD, it lacked sufficient evidence to recommend its use41.
Recently, it has been determined that the lung area increases 18–fold between 12 and 32 weeks, while the head circumference increases 4-fold42. In order to take this gestational age effect into account, the observed/expected LHR was introduced43,44. The normal observed/expected left and right lung ratio ranged from 61% to 139%. In fetuses with CDH, the mean observed/expected LHR is 39%44. As with the original lung-to-head ratio there has been insufficient critical analysis of the observed to expected lung-head ratio to recommend it for widespread clinical use.
With isolated CDH, 3–dimensional total fetal lung volume is significantly correlated with neonatal outcome (Fig. 9)45. 3D power Doppler permits an evaluation of pulmonary vasculature status46. In fetuses with CDH, there are a reduced number of pulmonary arteries per lung volume and muscularization of intra-acinar small arteries that result in pulmonary artery hypertension. Additional studies are required to determine if this sonographic technique is truly efficacious in the evaluation of fetuses with CDH.
In utero surgical repair of left–sided CDH without liver up did not improve outcome over postnatal therapy47. Any attempt at in utero repair with liver up CDH has resulted in fetal demise48.
Fetal tracheal occlusion has been performed for fetuses with CDH and herniation of the left lobe of the liver48. In order to achieve a sufficient effect, tracheal occlusion must be performed before 26 weeks’ gestation. The maximum effect from tracheal occlusion occurs at 4 weeks50. It has been estimated that tracheal occlusion improves survival with a left-sided CDH with liver up and low LHR from 24.1% to 49.1%51.
Fetal lung growth is closely correlated with fetal intra-tracheal pressure, indicating that one of the major stimulants of tracheal occlusion induced lung growth is mechanical52. Pulmonary vasculature is also improved after tracheal occlusion50.
The long–term outcome of infants with CDH is determined by the severity of pulmonary hypoplasia in the short–term and associated pulmonary hypertension over time53. There is associated persistent morbidity in up to 60% of surviors54.
In a population-based study from California in 1992, infant mortality with CDH was 56%55. Two studies20,56 reported an overall survival of 65%. A 2013 study from Japan has reported an overall survival rate of neonates with prenatally diagnosed isolated CDH of 70.8%29. Herniation of the liver and left-sided CDH decreases survival to around 50% and the absence of liver in the chest improves the overall survival to 76.5%56,57.The expertise of the neonatal intensive care unit caring for the affected infant also has a significant impact on postnatal survival.
The acknowledged high mortality with congenital diaphragmatic hernia is due: 1) associated anomalies; 2) pulmonary hypoplasia; and 3) persistent pulmonary hypertension.
After repair, the growth the of the diaphragm is impaired and exacerbates the decreased profusion of the ipsilateral lung and scoliosis58.
Tracheobronchial motility is also important in lung development. Tracheal innervation is deficient in animals with congenital diaphragmatic hernias. The deficiency in innervation may contribute to, not only pulmonary hypoplasia, but also long-term bronchopulmonary sequelae59.