*Dept. of Obstetrics and Gynecology, Clinical Center Novi Sad, Yugoslavia

^#St. Joseph Women's Hospital, Tampa Florida

Definition: A group of defects in which some parts of the abdominal contents protrude into the chest cavity.

Prevalence: The incidence of most common, posterolateral hernia is 1.5-2:10.000 births, with M:F ratio 2:1.

There are four types of hernias:

1.      Posterolateral defect, or Bochdalek hernia, accounts for about 90% of cases found in the neonatal period. It occurs on the left side in 80% of cases, on the right in 15% and may be bilateral in approximately 5%.

2.      Parasternal defect, or Morgagni hernia, is located on the anterior portion of the diaphragm and accounts for 1-2% of cases. It is more often right sided or bilateral, and usually contains liver.

3.      Septum transversum defect occurs because of a defect of the central tendon2.

4.      Hiatal hernias, occurring through a congenitally large esophageal orifice

5.      Eventration of the diaphragm occurs in 5% of cases and it is more commonly reported on the right. It has a similar pathophysiologic sequence, but in this case the abdominal contents move upwards because of a congenitally weak diaphragm that cannot hold them on their place2.

Embryology: The gut is returning from the yolk sac between 10 and 12 weeks of gestation and by that time the formation of the diaphragm should be completed. Two proposed mechanisms of the abnormality formation are:

·        delayed closure of the communication between the thorax and the abdomen, which could allow the abdominal contents to pass into the thoracic cavity, thus preventing the diaphragm to close1^,2 and

·        a primary diaphragmatic defect2.

In about 50% of the cases congenital diaphragmatic hernia may not occur before the 24^th week, when the pressure in the abdomen is higher, and this is probably the cause of the low detection rate at the 18-20 weeks scan.  The presence nuchal translucency at the 11-14 weeks scan suggests a poorer prognosis[3].

Inheritance patterns: Generally sporadic. For isolated defects in siblings the recurrence risk is less than 2%, due to multifactorial inheritance[4]^,[5],[6]. Rare families have shown dominant and X-linked recessive inheritance for isolated defects. Familial cases have a tendency towards bilateral lesions and tend to have less severe associated anomalies2. There is also a familial diaphragmatic agenesis, an autosomal recessive syndrome which appears to be a distinct clinical entity with a worse prognosis than posterolateral diaphragmatic hernia[7].

Diagnosis: The prenatal ultrasound diagnosis by ultrasound is based on:

1.      abdominal organs seen within the thoracic cavity. A left-sided hernia may be diagnosed by observing the stomach or loops of bowel to be partially or totally within the thorax

2.      Shift in the position of the heart / cardiac compression

3.      Polyhydramnios is a common associated finding, rarely observed before 24 weeks gestation. It is thought to be due either to esophageal compression, {kinking of the stomach} or reduced absorption of fluid by the hypoplastic lungs.

A right-sided hernia may be harder to diagnose because of the similar echogenicity of the lung and liver tissue, but the condition should be suspected by the presence of mediastinal shift or hydrothorax. Other signs include an abnormal position of the gallbladder, hepatic veins or even umbilical veins.

Associated anomalies: The incidence of associated abnormality reported prenatally is higher than that reported in the literature by pediatric surgeons and lower than those reported in post-mortem studies. In prenatal series only about 50% of fetuses have an isolated diaphragmatic defect. The difference is due to the fact that majority of fetuses with severe associated anomalies die in utero.

In about 25% of cases there is a chromosomal abnormality, usually Trisomy 21 and 18, and in another 25% there is a major defect including:

·        Cardiovascular defects (ASD, VSD, hypoplastic left heart, tetralogy Fallot, transposition)

·        Facial defects (oral cleft)

·        Gastrointestinal defects (exomphalos, duodenal atresia)

·        Renal anomalies (hydronephrosis, renal agenesis, polycystic kidneys, duplex kidneys)

·        Neural tube defects (anencephaly, cephalocele, spina bifida)2.

Differential diagnosis: The differential diagnosis includes other cystic chest lesions such as1:

·        cystic adenomatoid malformation

·        bronchogenic cysts

·        tumors

·        neurenteric cyst.

Management of pregnancy: The necessary examinations and consultations include1:

1.      fetal karyotyping

2.      expert ultrasound examination

3.      fetal echocardiography

4.      consultation with pediatric surgeon

These investigations should be performed even in the third trimester of pregnancy, because knowledge that the fetus is chromosomally and otherwise structurally normal allows the parents, obstetrician, pediatrician and surgeon to discuss the appropriate mode, place and timing of delivery. If the fetus is found to be chromosomally abnormal, obstetric intervention such as caesarean section may be avoided.

Prognosis: The primary determinant of survival is the presence of associated anomalies, pulmonary hypoplasia and pulmonary hypertension. The mortality has remained high despite optimal postnatal management and the introduction of extracorporal membrane oxygenation (ECMO). Prenatally discovered cases and cases diagnoses before 24 weeks have poorer prognosis because of the stage of the lung development in which the anomaly has occurred. At that period not only the respiratory airways are affected, causing the postnatal pulmonary hypoplasia, but also the reduction of number of vessels takes place, resulting postnatally in pulmonary hypertension^1,2. Mortality in this group is as high as 60 - 80%1^,[14].

Antenatal prediction of pulmonary hypoplasia remains one of the challenges of prenatal diagnosticians because this would be vital in both counseling parents and also in selecting those cases that may benefit from prenatal surgery. Poor prognostic signs are:

1.      Chromosomal abnormalities

2.      Associated anomalies

3.      Major mediastinal shift, which is considered to be significant if in a transverse section of the fetal thorax the heart is found to be entirely in either hemisphere created by an imaginary line between the sternum and the spine.

4.      Polyhydramnios, but this is a relatively late manifestation of the disease and its value has been disputed

Fetuses with congenital diaphragmatic hernia who have a "poor prognosis†with postnatal treatment now can be thus be identified on the basis of liver herniation, early diagnosis (before 25 weeks gestation) and, if it is a left sided congenital diaphragmatic hernia , a low healthy lung-to-head ratio (LHR).

If the lung-to-head ratio is 1 or less, the prognosis is very grim, despite ECMO, whereas if it is greater than 1.4, it is much better. Lung-to-head ratio values between 1.0 to 1.4 were associated with 38% survival and in majority of cases they required ECMO. Overall, survivors have a mean lung-to-head ratio of 1.4 +/- 0.33 and nonsurvivors, 1.05 +/- 0.3 [15].

Postnatal survival is significantly less in the cases where the liver has also moved up to the thorax [16].

Some studies suggest that left heart underdevelopment is associated with poor outcome, but fetal echocardiographic variables have not been conclusively proven to be good predictors of postnatal survival [17].

It seems that no prenatal sonographic parameter is absolutely predictive of postnatal death except very small healthy lung size [18].

Prenatal surgery: Postnatal complications in cases with DH result from a mechanical space-occupying lesion effect, with lung hypoplasia and hypertension, as well as decreased lung expansion with respiration. Based on these premises, prenatal treatment has been proposed to avoid pulmonary hypoplasia. There is extensive experience with in utero surgery for DH in experimental models. However, surgery requires a hysterotomy and subsequent caesarean section on an otherwise healthy mother with significant morbidity and risk of premature labor. A recent randomized clinical trial concluded that open fetal surgery, while physiologically sound and technically feasible, but does not improve survival over standard postnatal treatment in the subgroup of congenital diaphragmatic hernia fetuses without liver herniation ¹⁹. These data suggest that fetuses who have prenatally diagnosed congenital diaphragmatic hernia without evidence of liver herniation should be treated postnatally[19]. Recently the use of fetoscopic fetal tracheal occlusion has been advocated with the rationale of preventing outward movement of pulmonary fluid; retention of the fluid within the lungs and their expansion could cause reduction of the visceral contents back into the peritoneal cavity. In addition, the placement of a "tracheal clip†accelerates lung growth and avoids the often-fatal pulmonary hypoplasia[20] Preterm labor and other complications of open fetal surgery may in turn be avoided by using endoscopic fetal surgery to achieve the tracheal occlusion. This approach would obviate the need for a large uterine incision, possibly reduce the overall risks of the surgery.[21].. The best candidates for this procedure are fetuses with a left congenital diaphragmatic hernia who have liver herniation and a low lung-to-head ratio that are at high risk of neonatal demise. Tracheal clip placement via endoscopic fetal surgery appears to have better results than those in fetuses operated with open fetal surgery, although these differences are not statistically significant.[22]. A minimally-invasive intraluminal tracheal occlusion technique, which avoids laparotomy, hysterotomy and fetal neck dissection, has been recently accomplished[23]. This technique may change the surgical approach to the fetus with severe congenital diaphragmatic hernia.

References:

[14] Harrison MR, Adzick NS, Bullard KM, Farrell JA, Howell LJ, Rosen MA, Sola A, Goldberg JD, Filly RA. Correction of congenital diaphragmatic hernia in utero VII: a prospective trial. J Pediatr Surg 1997 Nov;32(11):1637-42.