Congenital diaphragmatic hernia (CDH) is a defect in any part of diaphragm, commonly left posterolateral defect. The incidence of CDH is 1:2500.[1] After correction of pulmonary hypertension, surgical repair is the only option. Development of the normal diaphragm is usually completed by the 10^th week of human embryogenesis [2].The precise embryologic basis of CDH remain controversial, although a number of animal models have been developed that have allowed the generation of various hypotheses for its origin. Initially, the cases of CDH were thought to result from a non-fusion of the different parts of the diaphragm. A successive hypothesis for the CDH origin has attributed abnormal lung development as instrumental to subsequent diaphragmatic defect, which had to be discredited since the transgenic mice with no lungs still demonstrated normal diaphragmatic development. A proliferative abnormality of the pleuroperitoneal folds with a failure to fuse with the post-hepatic mesenchyme has been implicated as the mechanism for the occurrence of CDH by subsequent studies. Recent proposal relies on  the double-hit hypothesis, which explains that the pulmonary development may already be defective before the hernia develops because of a “second developmental error” [3].

The pathophysiology of CDH is comprised of fixed (pulmonary and vascular hypoplasia) and reversible (pulmonary vascular reactivity) components. Lungs in severe CDH have markedly abnormal pulmonary vasculature. The peripheral pulmonary arteries are hypermuscular. This increased muscularity results in increased pulmonary vasoreactivity. As hypoxemia and acidosis stimulate further pulmonary vasospasm, a ‘vicious cycle’ is initiated with rapid clinical deterioration of the patient and inability to ventilate using the conventional techniques [4].

In most developed countries, up to two thirds of the CDH cases are diagnosed during the routine antenatal ultrasonographic (US) testing in the second or third trimester. The definitive sonographic diagnosis of fetal CDH relies on visualization of the abdominal organs in the fetal chest. The sonographic hallmark of a left CDH is a fluid-filled stomach just behind the left atrium and ventricle in the lower thorax as seen on a transverse view. Right CDH is more frequently missed or misdiagnosed and it may be confused with a solid mass such as a congenital cystic adenomatoid malformation in the chest [5]. MRI is rarely needed for the definitive diagnosis of CDH when US is equivocal, but its proven value lies in its ability in allowing the precise measurements for predicting the prognosis. MRI can assess fetal lung volumes, which even 3- dimensional US may fail to elucidate. This measurement can be used as a marker for the severity of the pulmonary hypoplasia and the need for extracorporeal membrane oxygenation (ECMO) in early (<28 weeks) as well as late gestation [6]. Chronic lung disease and the need for ECMO therapy are slightly better predicted by combined measurement of the observed to expected lung head ratio and the observed to expected fetal lung volumes as assessed by the MRI [7].

The traditional surgical management of CDH consists of repair through laparotomy. In the last decade, however, minimal access surgery (MAS) has gained wider popularity. Multiple studies show a higher recurrence rate associated with thoracoscopic repair [8]. Furthermore the surgical difference between open and thoracoscopic repair is that the rim of diaphragm is mostly adhered to the dorsal pleuroperitoneal canal and preparation from thoracic side is challenging.

From the abdominal route preparation is much easier and more obvious, while from thoracic route these structures are harder to find. Yet, thoracoscopy renders smooth postoperative recovery in terms of reduction in ventilator requirements, good pain relief, short hospital stay and good cosmesis. Overall results of thoracoscopy are better than the open surgical patients of CDH with cardiovascular stability [9].

References:

1. Engum SA, Kogon B, Jensen E, Isch J, Balanoff C, Grosfeld JL. Gastric tonometry and direct intraabdominal pressure monitoring in abdominal compartment syndrome. J Pediatr Surg. 2002;37:214–8. [PubMed]
2. Clugston RD, Greer JJ. Diapghram development and congenital diaphragmatic hernia. Seminars in Pediatr Surg 2007; 16: 94-100.
3. Haroon J, Chamberlain RS. An evidence-based review of the current treatment of congenital diaphragmatic hernia. Clin Pediatr 2013; 52: 115-24.
4. Hedrick HL. Management of prenatally diagnosed congenital diaphragmatic hernia. Semin Pediatr Surg 2013; 22: 37-43.
5. Witters I, Legius E, Moerman P, Deprest J, Van Shoubroeck D, Timmerman D, et al. Associated malformations and chromosomal anomalies in 42 cases of prenatally diagnosed diaphragmatic hernia. Am J Med Genet 2001; 103: 278-282.
6. Walleyo A, Debus A, Kehl S, Weiss C, Schonberg SO, Schaible T, et al. Periodic MRI lung volume assessment in fetuses with congenital diaphragmatic hernia: prediction of survival, need for ECMO, and development of chronic lung disease. AJR Am J Roentgenol 2013 ; 201: 419-26.
7. Schaible T, Büsing KA, Felix JF, Hop WCJ, Zahn K, Wessel L, et al. Prediction of chronic lung disease, survival and need for ECMO therapy in infants with congenital diaphragmatic hernia: additional value of fetal MRI measurements? Eur J Radiol 2012; 81: 1076-82.
8. Vijfhuize S, Deden AC, Costerus SA, Sloots CE, Wijnen RM. Minimal access surgery for repair of congenital diaphragmatic hernia: is it advantageous? An open review. Eur J Pediatric Surg. 2012;22:364–373.
9. Costerus S, Zahn K, Ven K, Vlot J, Wessel L, Wijnen R. Thoracosopic versus open repair of CDH in cardiovascular stable neonates. Surg Endosc 2016; 30: 2818-2824