Fetal tracheal occlusion in the rat model of nitrofen-induced congenital diaphragmatic hernia

Update on Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a rare developmental defect of the diaphragm, characterized by herniation of abdominal contents into the chest that results in varying degrees of pulmonary hypoplasia and pulmonary hypertension (PH). Significant advances in the prenatal diagnosis and identification of prognostic factors have resulted in the continued refinement of the approach to fetal therapies for CDH. Postnatally, protocolized approaches to lung-protective ventilation, nutrition, prevention of infection, and early aggressive management of PH have led to improved outcomes in infants with CDH. Advances in our understanding of the associated left ventricular (LV) hypoplasia and myocardial dysfunction in infants with severe CDH have allowed for the optimization of hemodynamics and management of PH. This article provides a comprehensive review of CDH for the anesthesiologist, focusing on the complex pathophysiology, advances in prenatal diagnosis, fetal interventions, and optimal postnatal management of CDH.

Lung function and pulmonary artery blood flow following prenatal maternal retinoic acid and imatinib in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND

Lung and pulmonary vascular maldevelopment in congenital diaphragmatic hernia (CDH) results in significant morbidity and mortality. Retinoic acid (RA) and imatinib have been shown to improve pulmonary morphology following prenatal administration in the rat nitrofen-induced CDH model. It remains unclear if these changes translate into improved function. We evaluated the effect of prenatal RA and imatinib on postnatal lung function, structure, and pulmonary artery (PA) blood flow in the rat CDH model.

METHODS

Olive oil or nitrofen was administered alone or in combination with RA or imatinib to pregnant rats. Pups were assessed for PA blood flow by ultrasound and pulmonary function/morphology following delivery, intubation, and short-term ventilation.

RESULTS

Neither RA nor imatinib had a negative effect on lung and body growth. RA accelerated lung maturation indicated by increased alveoli number and thinner interalveolar septa and was associated with decreased PA resistance and improved oxygenation. With the exception of a decreased PA pulsatility index, no significant changes in morphology and pulmonary function were noted following imatinib.

CONCLUSION

Prenatal treatment with RA but not imatinib was associated with improved pulmonary morphology and function, and decreased pulmonary vascular resistance. This study highlights the potential of prenatal pharmacologic therapies, such as RA, for management of CDH.

Fetal tracheal occlusion in mice: a novel transuterine method

BACKGROUND

Fetal tracheal occlusion (TO) is an emerging surgical therapy in congenital diaphragmatic hernia that improves the fetal lung growth. Different animal models of congenital diaphragmatic hernia and TO present advantages and disadvantages regarding ethical issues, cost, surgical difficulty, size, survival rates, and available genetic tools. We developed a minimally invasive murine transuterine TO model, which will be useful in defining how TO impacts lung molecular biology, cellular processes, and overall lung physiology.

MATERIALS AND METHODS

Time-mated C57BL/6 mice underwent laparotomy at embryonic day 16.5 (E16.5) with transuterine TO performed on two fetuses in each uterine horn. At E18.5, dams were sacrificed and fetuses harvested. The lungs of the TO fetuses were compared with the nonmanipulated counterparts by morphometric and histologic analysis.

RESULTS

Successful TO was confirmed in 16 of 20 TO fetuses. Twelve of them survived to E18.5 (75%). Fetal weights were comparable, but lung weights were significantly greater in TO (28.41 ± 5.87 versus 23.38 ± 3.09, P = 0.043). Lung to body weight ratio was also greater (0.26 ± 0.003 versus 0.22 ± 0.002, P = 0.006). E18.5 TO lungs demonstrated dilated central and distal airspaces with increased cellularity. DNA/protein and DNA/lung weight ratios were elevated while protein/lung weight ratio was lower in TO compared to control.

CONCLUSIONS

Mice fetal transuterine TO is feasible with comparable outcomes to other current animal models. The increase in the lung weight, lung to body weight ratio and the DNA/protein ratio indicate organized lung growth rather than edema or cell hypertrophy.

Minimally Invasive Fetal Surgery

Fetal surgery corrects severe congenital anomalies in utero to prevent their severe consequences on fetal development. The significant risk of open fetal operations to the pregnant mother has driven innovation toward minimally invasive procedures that decrease the risks inherent to hysterotomy. In this article, we discuss the basic principles of minimally invasive fetal surgery, the general history of its development, specific conditions and procedures used to treat them, and the future of the field.

Suggested Mechanisms of Tracheal Occlusion Mediated Accelerated Fetal Lung Growth: A Case for Heterogeneous Topological Zones

In this article, we report an up-to-date summary on tracheal occlusion (TO) as an approach to drive accelerated lung growth and strive to review the different maternal- and fetal-derived local and systemic signals and mechanisms that may play a significant biological role in lung growth and formation of heterogeneous topological zones following TO. Pulmonary hypoplasia is a condition whereby branching morphogenesis and embryonic pulmonary vascular development are globally affected and is classically seen in congenital diaphragmatic hernia. TO is an innovative approach aimed at driving accelerated lung growth in the most severe forms of diaphragmatic hernia and has been shown to result in improved neonatal outcomes. Currently, most research on mechanisms of TO-induced lung growth is focused on mechanical forces and is viewed from the perspective of homogeneous changes within the lung. We suggest that the key principle in understanding changes in fetal lungs after TO is taking into account formation of unique variable topological zones. Following TO, fetal lungs might temporarily look like a dynamically changing topologic mosaic with varying proliferation rates, dissimilar scale of vasculogenesis, diverse patterns of lung tissue damage, variable metabolic landscape, and different structures. The reasons for this dynamic topological mosaic pattern may include distinct degree of increased hydrostatic pressure in different parts of the lung, dissimilar degree of tissue stress/damage and responses to this damage, and incomparable patterns of altered lung zones with variable response to systemic maternal and fetal factors, among others. The local interaction between these factors and their accompanying processes in addition to the potential role of other systemic factors might lead to formation of a common vector of biological response unique to each zone. The study of the interaction between various networks formed after TO (action of mechanical forces, activation of mucosal mast cells, production and secretion of damage-associated molecular pattern substances, low-grade local pulmonary inflammation, and cardiac contraction-induced periodic agitation of lung tissue, among others) will bring us closer to an appreciation of the biological phenomenon of topological heterogeneity within the fetal lungs.

Airway and vascular maturation stimulated by tracheal occlusion do not correlate in the rabbit model of diaphragmatic hernia

BACKGROUND

In animal models of congenital diaphragmatic hernia (CDH), tracheal occlusion (TO) has induced maturation of both airway spaces and vascular structures. Airway and vascular response to TO are assumed to occur in parallel. This study aims to describe and measure the relationship between airway and vascular maturation induced by TO.

METHODS

A rabbit model of CDH on gestational day (GD) 23 and TO on GD 28 (term = GD 31) has been used. Two study groups have been defined: DH (diaphragmatic hernia) and TO (DH treated with TO). Animals were collected on GD 30 and blood flow data of the pulmonary artery (pulsatility index (PI) and fractional moving blood volume) were ultrasonographically measured. Lung morphometry consisted of measurements of radial alveolar count (RAC) and arterial muscular thickness.

RESULTS

Animals in the DH group (n = 9) had the worst hemodynamic parameters; their lungs were hypoplastic and had the thickest arterial muscular layer. Animals in the TO group (n = 10) had all these effects reversed. There were no correlations among hemodynamic, airway, and vascular parameters, except for RAC and PI (r = -0.528, P = 0.043).

CONCLUSION

Airway and vascular maturation after TO appear to be uncorrelated effects. TO could trigger several pathways that separately regulate airway and vascular responses.

Management of prenatally diagnosed congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly that presents with a broad spectrum of severity that is dependent upon components of pulmonary hypoplasia and pulmonary hypertension. While advances in neonatal care have improved the overall survival of CDH in experienced centers, mortality and morbidity remain high in a subset of CDH infants with severe CDH. Prenatal predictors have been refined for the past two decades and are the subject of another review in this issue. So far, all randomized trials comparing prenatal intervention to standard postnatal therapy have shown no benefit to prenatal intervention. Although recent non-randomized reports of success with fetoscopic endoluminal tracheal occlusion (FETO) and release are promising, prenatal therapy should not be widely adopted until a well-designed prospective randomized trial demonstrating efficacy is performed. The increased survival and subsequent morbidity of CDH survivors has resulted in the need to provide resources for the long-term follow up and support of the CDH population.

Advances in prenatal diagnosis and treatment of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common birth anomaly. Absence or presence of liver herniation and determination of lung-to-head ratio are the most accurate predictors of prognosis for fetuses with CDH. Though open fetal CDH repair has been abandoned, fetal endoscopic balloon tracheal occlusion promotes lung growth in fetuses with severe CDH. Although significant improvements in lung function have not yet been shown in humans, reversible or dynamic tracheal occlusion is promising for select fetuses with severe CDH. This article reviews advances in prenatal diagnosis of CDH, the experimental basis for tracheal occlusion, and its translation into human clinical trials.

Management of prenatally diagnosed congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly that presents with a broad spectrum of severity dependent upon components of pulmonary hypoplasia and pulmonary hypertension. While advances in neonatal care have improved the overall survival of CDH in experienced centers, mortality and morbidity remain high in a subset of CDH infants with severe CDH. The most important prenatal predictor of outcome in left-sided CDH is liver position. More precise and reproducible prenatal predictive parameters need to be developed to allow standardization of results between centers and appropriate design of clinical trials in CDH. Thus far, all randomized trials comparing prenatal intervention to standard postnatal therapy have shown no benefit to prenatal intervention. Although recent non-randomized reports of success with balloon tracheal occlusion (and release) are promising, prenatal therapy should not be widely adopted until a well-designed prospective randomized trial demonstrating efficacy is performed. The increased survival and subsequent morbidity of CDH survivors has resulted in the need to provide resources for the long-term follow-up and support of the CDH population.

Tracheal occlusion for fetal congenital diaphragmatic hernia: the US experience

Congenital diaphragmatic hernia (CDH) is characterized by a defect in the diaphragm that permits abdominal viscera to herniate into the chest. These herniated viscera are thought to compress the growing lung and cause lung parenchymal and vascular hypoplasia. The genetic defects that cause the diaphragmatic defect may also contribute primarily to lung hypoplasia. Postnatal reduction of the herniated abdominal viscera and correction of the diaphragmatic defect are easily achievable, but the lung hypoplasia persists, often leading to persistent fetal circulation and respiratory failure. This article reviews the experimental basis of fetal therapy for CDH and the US clinical experience with tracheal occlusion.

Antenatal prediction of lung volume and in-utero treatment by fetal endoscopic tracheal occlusion in severe isolated congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a severe malformation with an overall survival between 30% and 90%. Survival in the presence of associated malformations is very low. The condition should be detected in ultrasound screening programmes, but whether and how prenatal imaging can accurately predict outcome remains a matter of debate. Predictions based on the lung area:head circumference ratio and liver position are best studied. This information is highly relevant in counselling patients, leaving to severe cases the option of termination of pregnancy as experimental prenatal intervention aiming to reverse pulmonary hypoplasia. The purpose of this review is to update current knowledge regarding predictive value of prenatal assessment in terms of neonatal survival. We will also discuss experimental evidence and clinical data regarding fetal tracheal occlusion.

Fetal tracheal occlusion for severe congenital diaphragmatic hernia in humans: a morphometric study of lung parenchyma and muscularization of pulmonary arterioles

OBJECTIVE

The aim of this study is to examine structure of lung parenchyma (Pp) and muscularization of pulmonary arterioles (PAs) in human fetuses that underwent tracheal occlusion (TO) therapy for severe congenital diaphragmatic hernia (CDH).

MATERIAL

Fifteen fetuses underwent TO, with 5 survivors (Am J Obstet Gynecol. 2000:183;1059-1066). Paraffin-embedded lung specimens from 7 of 10 nonsurvivors (CDH-TO) and 6 age-matched fetuses (CDH) were available for morphometric analysis, which included measurements of point fraction of lung Pp and surface density. The PAs were categorized according to external diameter (<70 microm and 70 <or= 140 microm). Percent medial wall thickness (%MWT) was calculated by dividing raw measurements of MWT by external diameter.

RESULTS

Gestational age at TO was 27.6 +/- 0.9 weeks with a mean duration of TO of 32.6 +/- 6.8 days. Gestational age at delivery (CDH-TO 31.9 +/- 0.9 vs CDH 35.4 +/- 1.8 weeks; P = .18) and postnatal survival time (CDH-TO 20.5 +/- 6.0 vs CDH 18.6 +/- 7.8 days; P = .85) were not significantly different between groups. Tracheal occlusion significantly increased the lung-to-body weight ratio (CDH-TO 13.0 +/- 2.2 vs CDH 6.6 +/- 0.9; P = .02). Tracheal occlusion tended to decrease right-lung Pp (CDH-TO 54.6% +/- 2.6% vs CDH 65.7% +/- 5.9%; P = .05), whereas left-lung Pp was not different between groups (CDH-TO 63.0% +/- 3.5% vs CDH 66.7% +/- 4.1%; P = .51). Surface density of airspaces was not different between groups in either left (CDH-TO 171.3 +/- 16.1 cm(-1) vs CDH 151.1 +/- 8.1 cm(-1); P = .34) or right (CDH-TO 172.0 +/- 10.6 cm(-1) vs CDH 160.8 +/- 3.6 cm(-1); P = .33) lungs. The %MWT in small and large PA was similar between groups.

CONCLUSIONS

Open prenatal TO in human fetuses increased lung growth, as evidenced by an increase in lung weight, but did not improve parenchymal structure or muscularization of PAs.

NKCC-1 and ENaC are down-regulated in nitrofen-induced hypoplastic lungs with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is accompanied by pulmonary hypoplasia and pulmonary hypertension. Fetal lung growth is dependent on the secretion of lung liquid, which normally is absorbed at partus. The ion channel NKCC-1 is involved in this secretory process, but has recently also been reported to be implicated in absorption. CDH patients show a disturbed transition from secretion to absorption. alpha- and beta-ENaC are essential for lung liquid absorption. Common for all transcellular ion transport is the need for Na/K-ATPase as a primary driving force. The aim of the study was first to map the normal pulmonary expression of the above proteins during late gestation and secondly to see if the expression was affected in a CDH rat model. Pregnant Sprague-Dawley rat dams were given nitrofen on gestational day 9.5 to induce CDH. The fetuses were removed on gestational days E18 and E21. In addition, newborn rats were harvested postpartum on day P2. The fetuses were put into one of two groups: hypoplastic lungs without CDH (N-CDH) and hypoplastic lungs with CDH (N+CDH). The pulmonary expression of NKCC-1, alpha-/beta-ENaC and Na/K-ATPase was then analyzed using Western blot. We found that the protein levels of NKCC-1 on gestational days E18 and E21 were significantly lower among fetuses with N+CDH as well as N-CDH compared to controls. The expression of beta-ENaC was also significantly down-regulated in both the groups on E18 and E21. The protein levels of alpha-ENaC and Na/K-ATPase were not found to be significantly decreased, but both showed a tendency towards down-regulation. The marked down-regulation of NKCC-1 in fetal hypoplastic lungs with CDH indicates a possibly decreased lung liquid production. This may be one of the mechanisms behind the disturbed pulmonary development in CDH. We also show that beta-ENaC is down-regulated. Down-regulation of beta-ENaC may result in abnormal lung liquid absorption, which could be one of the mechanisms behind the respiratory distress seen in CDH patients postpartum.

Increased distension stimulates distal capillary growth as well as expression of specific angiogenesis genes in fetal mouse lungs

Tracheal occlusion (TO) performed surgically in utero near the end of gestation causes a rapid increase in the distension of future airspaces, resulting in accelerated lung development. The authors hypothesize that TO stimulates microvascular growth concomitant with a rapid increase in the expression of genes implicated in angiogenesis. Mouse fetuses underwent in utero surgery (TO or sham-TO surgery) at 16.5 days of gestation, whereupon development was allowed to continue for a further 1 or 24 hours. Microvascular changes were assessed by immunohistochemical staining of fetal lung sections for platelet endothelial cell adhesion molecule-1. Levels of vascular endothelial growth factor-A (VEGF-A; isoforms 120, 164 and 188), VEGF receptors 1 and 2 (VEGFR-1 and -2), angiopoietins 1 and 2, and Tie2 mRNAs were determined by quantitative real-time polymerase chain reaction (PCR). The authors observed more intercapillary interconnection, less isolated capillaries, and a more extended capillary network inside septa of lungs that underwent 24 h of TO versus sham-TO. Moreover, the authors observed a significant increase in mRNA levels of VEGF 188 and VEGFR-1 as early as 1 hour following TO and of VEGFR-1 and angiopoietin 1 after 24 hours. Together, these results suggest that surgically applied stretching quickly enhances the expression of specific angiogenesis and vessel maintenance genes, which seems to result in the maturation and organization of a more extensive and complex capillary network.

Fetal Tracheal Occlusion for the Treatment of Congenital Diaphragmatic Hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) continues to be associated with significant mortality and morbidity rates despite advances in neonatal care. Fetal intervention for CDH has been studied for 25 years. After initial difficulties encountered with open fetal repair, attention has turned to tracheal occlusion (TO) as a method to correct pulmonary hypoplasia before birth. This article reviews our contribution to this field of research and outlines the current status of this treatment modality.

MATERIALS AND METHODS

Using the fetal lamb model, we have studied the effects of fetal TO on tracheal fluid pressure, lung growth and type II pneumocyte maturation, and surfactant production. We developed a minimally invasive and reversible technique of TO, using a detachable balloon placed using single-port tracheoscopy. We examined differential lung growth, structural maturation, pulmonary artery remodeling, and lung function during an 8-h resuscitation period in lambs, comparing normal controls, lambs with a surgically created CDH, those with CDH+TO, and those with CDH+TO and release of TO 1 week before delivery. We also studied the potential benefits of maternal betamethasone administration and the administration of surfactant at birth. Using a neonatal piglet model, we examined the effect of postnatal pulmonary distension with perfluorocarbon on lung growth. More recently, we turned to the rat nitrofen-induced CDH model to study the effects of TO on bronchial branching and some molecular markers of lung growth (Shh and LGL1).

CONCLUSIONS

Fetal TO is being used to treat human CDH, but its application remains limited by the absence of reliable and widely reproducible prenatal prognostic criteria. A better understanding of the molecular events guiding the lung growth seen with TO may help to refine its use in humans.

Prenatal intervention for congenital diaphragmatic hernia

Advances in prenatal ultrasound have revealed the poor natural history of fetal congenital diaphragmatic hernia (CDH) and its hidden mortality during gestation and immediately after birth. Attempts to improve this poor outcome led to the development of prenatal surgical intervention for severe CDH by Harrison and his colleagues at the University of California San Francisco. Prenatal surgical intervention for CDH has seen four phases: open fetal surgical repair, open surgical tracheal occlusion, endoscopic external tracheal occlusion, and endoscopic endoluminal tracheal occlusion. After extensive work in the laboratory, prenatal intervention has been applied in humans since 1984. With the most recent techniques, maternal risk is significantly reduced as is the incidence of preterm labor. In the meantime, the survival rate of fetuses with CDH without fetal intervention has improved mainly due to the minimization of iatrogenic lung injury by gentle ventilation, first described in 1985. However, the morbidity of the survivors with severe CDH remains high. Prenatal intervention for CDH will be justified if improvement in survival or morbidity can be demonstrated when compared to planned delivery and postnatal management with gentle ventilation strategy.

Tracheal occlusion: A review of obstructing fetal lungs to make them grow and mature

Fetal lung growth and functional differentiation are affected strongly by the extent that pulmonary tissue is distended (expanded) by liquid that naturally fills developing future airspaces. Methods that prevent normal egress of this lung fluid through the trachea magnify mechanical stretching of lung parenchymal cells, thereby promoting lung development. Indeed, experimental observations demonstrate that in utero tracheal occlusion (TO) performed on fetuses during the late canalicular-early saccular stage potently stimulates pulmonary growth and maturation. In this review, we present the four principle non-human animal models of TO/obstruction and discuss them in relation to their utility in elucidating lung development, in remedying congenital diaphragmatic hernia (CDH) as well as in investigating the stretching effects on growth and remodeling of the fine vasculature.

Tracheal occlusion in fetal rats alters expression of mesenchymal nuclear transcription factors without affecting surfactant protein expression

BACKGROUND/PURPOSE

Mesenchymal nuclear transcription factors (MNTF) are involved in lung development and maturation and regulate surfactant protein (SP) expression. Prolonged (>2 weeks) fetal tracheal occlusion (TO) has been shown to accelerate lung growth and inhibit pulmonary surfactant synthesis. The effects of TO on SP expression and MNTF, however, have not been formally assessed. The objectives of this study were to evaluate the effects of short-term (3 days) TO on normal lung growth and protein expression of pulmonary MNTF involved in SP synthesis.

METHODS

At E19 (term, 22 days), 2 fetuses per time-dated Sprague-Dawley rats underwent either TO (n = 23) or a sham (n = 22) operation. Lungs were harvested 72 hours post surgery. Pulmonary SP-A; SP-B; SP-C messenger RNA (mRNA) expression; and SP-A and SP-B, Hoxb5, thyroid transcription factor 1, and retinoic X receptor-alpha protein expression were analyzed.

RESULTS

Lung weight was significantly increased by TO (TO 0.32 +/- 0.02g vs SHAM 0.14 +/- 0.01 g; P < .001), resulting in 123% increase of the lung-to-body-weight ratio. No difference of SP-A-mRNA (177 +/- 4.3 TO vs 169 +/- 4.4 SHAM; P = .25), SP-B-mRNA (87.7 +/- 0.2 TO vs 87.4 +/- 0.02 SHAM; P = .33), and SP-C-mRNA (186.5 +/- 3.2 TO vs 183.2 +/- 2.7 SHAM; P = .45) expression was found. Surfactant protein A (175.6 +/- 25.3 TO vs 192.5 +/- 19.8 SHAM; P = .59) and SP-B (163.4 +/- 5.2 TO vs 166.8 +/- 9.3 SHAM; P = .75) protein expression were similar in both groups; however, Hoxb5 (70.3 +/- 18.9 TO vs 130.6 +/- 5.1 SHAM; P = .02) and thyroid transcription factor 1 (102.6 +/- 19 TO vs 181.1 +/- 6.3 SHAM; P = .007) expression were significantly decreased. Retinoic X receptor-alpha expression tended to be increased by TO (171.9 +/- 6.0 TO vs 155.4 +/- 6.7 SHAM; P = .06).

CONCLUSIONS

Short-term TO late in gestation induces rapid lung growth. Surfactant protein-mRNA and protein expression are not significantly altered. Thyroid transcription factor 1 and Hoxb5 are down-regulated by TO, suggesting that duration and timing of occlusion are important in balancing the effects of TO on lung growth vs lung maturation.

Changes in fetal lung distension alter expression of vascular endothelial growth factor and its isoforms in developing rat lung

Vascular endothelial growth factor A (VEGF-A) is essential for normal pulmonary vascular and parenchymal development. Changes in fetal lung distension profoundly affect lung growth and maturation, including vascular development. To define developmental lung expression of VEGF-A and its receptors and investigate effects of changes in fetal lung distension, we studied fetal rats at embryonic day (ED) 16, 19, and 22, postnatal rats at postnatal day (PD) 5, 10, and 21, and adult rats. We used reverse transcriptase PCR to measure mRNA expression for VEGF-A isoforms (VEGF-A(120), (-144), (-164), and (-188)) and VEGF-A receptors, Flt-1 and Flk-1. With advancing development, mRNA content increased only for VEGF-A(188) (p < 0.05) and for Flt-1 (p < 0.02) and Flk-1 (p < 0.005). As a percentage of total VEGF-A mRNA, VEGF-A(188) (15% at ED 16) increased to become the dominant isoform at PD 21 (40%, p < 0.005) and adulthood; in contrast, there were decreases in both VEGF-A(144) (p < 0.05) and (-120) (p < 0.005). VEGF-A protein was expressed in alveolar epithelium (type I and II cells) and interstitium. Increasing fetal lung distension by tracheal occlusion (TO) accelerated the normal maturational pattern of VEGF-A isoforms and increased VEGF-A protein; decreasing fetal lung distension by congenital diaphragmatic hernia (CDH) retarded the normal developmental pattern and decreased VEGF-A protein. Neither TO nor CDH consistently affected Flt-1 or Flk-1 mRNA content. These results show that mechanical factors significantly affect lung VEGF-A expression and suggest that VEGF-A mediates previously described changes in lung vascular and parenchymal development caused by CDH and by TO.

Congenital diaphragmatic hernia, tracheal occlusion, thyroid transcription factor-1, and fetal pulmonary epithelial maturation

Congenital diaphragmatic hernia (CDH) occurs in ∼1:2,500 human births and has high morbidity and mortality rates, primarily due to pulmonary hypoplasia and pulmonary hypertension. Tracheal occlusion (TO), in experimental animals, distends lungs and increases lung growth and alveolar type I cell maturation but decreases surfactant components and reduces alveolar type II cell density. We examined effects of CDH and CDH+TO on lung growth and maturation in fetal rats. To induce CDH, we administered nitrofen (100 mg) to dams at 9.5 days of gestation. We compared lungs from fetuses with CDH, CDH+TO, and those exposed to nitrofen without CDH. CDH decreased lung wet weight bilaterally ( P < 0.0001) and DNA content in lung ipsilateral to CDH ( P < 0.05). CDH+TO significantly increased lung wet weights bilaterally; DNA content was intermediate between CDH and NC. To evaluate effects on the distal pulmonary epithelium, we examined surfactant mRNA and protein levels, type I and II cell-specific markers (RTI40 and RTII70, respectively), and transcriptional regulator thyroid transcription factor-1 (TTF-1). Decreased lung distension (due to CDH) increased SP-C mRNA and TTF-1 protein expression and reduced RTI40 ( P < 0.05 for all). Increased lung distension (due to CDH+TO) reduced expression of SP mRNAs and pro-SP-C and TTF-1 proteins and enhanced expression of RTI40 (mRNA and protein; P < 0.05 for all). We conclude that CDH+TO partially reverses effects of CDH; it corrects the pulmonary hypoplasia and restores type I cell differentiation but adversely affects SP expression in type II cells. These effects may be mediated through changes in TTF-1 expression.

Rescue of the Hypoplastic Lung by Prenatal Cyclical Strain

We determined the effects of sustained and cyclical prenatal mechanical strain on the hypoplastic lung of the ovine model of congenital diaphragmatic hernia. Over a period of 4 weeks in late gestation, repeated cyclical tracheal occlusion for 23 hours with 1-hour release stimulated minimal growth, but promoted maturation with the development of a saccular lung. In contrast, a cycle consisting of 47 hours with 1-hour release induced optimal lung growth and morphologic maturation of the hypoplastic lung parenchyma. Sustained occlusion resulted in exaggerated lung growth, exceeding that of unaffected controls, and abnormal alveolar development. The extent of induction of lung growth by mechanical strain was inversely proportional to the number of alveolar type II cells remaining in the lung epithelium. These studies show that, although mechanical strain is capable of inducing lung growth and differentiation, cyclical strain is a prerequisite for normal development and that mechanically induced growth occurs at the expense of the alveolar type II cell. We conclude that cyclical strain may allow optimal alveolar development while maintaining a population of alveolar type II cells and may thus facilitate an improvement in postnatal lung function in infants with congenital diaphragmatic hernia.

Fetal surgery for lung lesions, congenital diaphragmatic hernia, and sacrococcygeal teratoma

After more than 2 decades of experimental and clinical work, fetal surgery is an accepted treatment option for highly selected fetuses with life-threatening anomalies. Fetal lung masses associated with hydrops are nearly 100% fatal. These lesions can be resected in utero if they are predominantly solid or multicystic. Thoracoamniotic shunt placement may be effective in the setting of a single large cyst. Fetuses diagnosed with left congenital diaphragmatic hernia before 26 weeks' gestation with associated liver herniation and a low right lung to head circumference ratio have a relatively poor prognosis with conventional therapy after birth, but in utero therapeutic approaches have yet to show a comparative survival benefit. A prospective randomized trial is required to critically evaluate the efficacy of fetal tracheal occlusion for severe diaphragmatic hernia. Fetal sacrococcygeal teratoma complicated with progressive high output cardiac failure may benefit from in utero resection of the tumor.

In vivo tracheal occlusion in fetal mice induces rapid lung development without affecting surfactant protein C expression

Fetal tracheal occlusion (TO) reverses lung hypoplasia by inducing rapid lung growth. Although increases in lung size accompanied by increased numbers of alveoli and capillaries have been reported, effects of TO on lung development have not been formally assessed. In the present study, the objective was to verify our prediction that the main effect of TO would be to accelerate fetal lung development. We have developed and characterized a new fetal mouse model of TO to best realize this goal. At embryonic day 16.5, pregnant CD1 mice were operated under general anesthesia. One fetus per dam was selected to undergo surgical TO with a surgical clip or a sham operation. The fetuses were delivered 24 or 36 h postsurgery. The maturation of lung parenchyma, evaluated by counting the generations of alveolar saccules from the terminal bronchiole to the pleura, was significantly accelerated in the TO group with a complexity of the gas exchange region comparable with postnatal days 1 and 3 after 24 or 36 h of TO. Cellular proliferation and apoptosis peaks, assessed by immunohistochemistry directed against PCNA and the active form of caspase-3, were significantly increased 24 h after surgery in the TO group compared with the sham group. However, in situ hybridization showed no significant difference in the density of type II pneumocytes expressing surfactant protein C mRNA. Our results show that brief TO during late gestation in fetal mice induces accelerated lung development with minimal effects on surfactant protein C mRNA expression.

The lung-to-head ratio and fetoscopic temporary tracheal occlusion: prediction of survival in severe left congenital diaphragmatic hernia

OBJECTIVES

To evaluate the reliability of sonographic lung-to-head ratio (LHR) measurement as a predictor of survival in fetuses with congenital diaphragmatic hernia (CDH) and to compare the probability of survival in those with temporary tracheal occlusion (TO) or standard care with respect to the LHR.

METHODS

Fifty-six fetuses with left CDH with liver herniated into the thorax at complete prenatal evaluation were included in logistic regression analyses of antenatal predictors of survival to hospital discharge. Sixteen subjects underwent TO and 40 received standard care.

RESULTS

LHR was a significant predictor of survival, with probability of survival increasing with increasing LHR (odds ratio (OR) 8.5, P = 0.04). When subjects with anomalies were excluded, the LHR effect was similar after adjustment for TO (OR 7.1, P = 0.11). Linear spline models suggested a plateau in survival at an LHR of 1.0 and all models suggested increased odds of survival with TO. Minimum LHR measurements had a high degree of inter- and intraobserver agreement (intraclass correlation coefficients of 0.70 and 0.80, respectively).

CONCLUSIONS

Calculation of the LHR in fetuses with CDH is a reliable and powerful predictor of survival to hospital discharge, although improving odds of survival may plateau at an LHR of 1.0. TO may have an independent benefit on survival to hospital discharge.

Down-regulation of sonic hedgehog expression in pulmonary hypoplasia is associated with congenital diaphragmatic hernia

The pathogenesis of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) is unknown. The sonic hedgehog (Shh) cascade is crucial for the patterning of the early respiratory system in mice. To establish whether Shh plays a role in the pathogenesis of lung hypoplasia in CDH, we investigated the gestation-specific expression of Shh in normal rat and human lungs using in situ hybridization and immunohistochemistry. The expression pattern was compared with that of age-matched samples of hypoplastic lungs associated with CDH in humans and in the 2,4-dichlorophenyl-p-nitrophenylether (nitrofen) rat model. Our results showed that in normal controls the expression of Shh increased with advancing gestation, peaked in the late pseudoglandular stage, and declined thereafter. The expression of Shh is initially down-regulated in pulmonary hypoplasia associated with CDH and peaks instead during the late canalicular stage. These data indicate that maximal expression of Shh occurs when respiratory bronchioles develop and thinning of the interstitium takes place, suggesting that Shh may play a role in these processes. Furthermore, we observed that Shh inhibited fetal lung fibroblast proliferation in vitro. Therefore, it is tempting to speculate that alterations in Shh expression may affect these developmental processes, thereby contributing to the pulmonary abnormality in CDH.

Fetal tracheal occlusion in the rat model of nitrofen-induced congenital diaphragmatic hernia: tracheal occlusion reverses the arterial structural abnormality

BACKGROUND/PURPOSE

The high mortality rate of congenital diaphragmatic hernia (CDH) is ascribed generally to pulmonary hypoplasia and persistent pulmonary hypertension characterized by associated pulmonary arterial structural changes. Prenatal tracheal occlusion (TO) accelerates lung growth, but the effect of TO on pulmonary arterial structure in CDH has not been well defined. The authors hypothesized that TO could reverse the pulmonary arterial structural changes observed in CDH. To address this hypothesis, we utilized the nitrofen-induced rat model of CDH to examine the effect of TO on pulmonary arterial morphology of CDH lungs.

METHODS

Left-sided CDH was induced by administering 100 mg of nitrofen to pregnant Sprague-Dawley rats on day 9 of gestation. TO was performed on day 19, and the fetuses were harvested on day 21.5 of gestation. After the ductus arteriosus was ligated, the pulmonary arteries were injected with a barium-gelatin mixture, and the lungs were inflation fixed. Coronal sections of the lungs were stained with elastin van Gieson. External diameter (ED), internal diameter (ID), and medial and adventitial wall thickness of the pulmonary arteries were measured using a computer image analyzer, and the percent medial thickness (%MT) and adventitial thickness (%AT) were calculated. The lungs from nitrofen-exposed fetuses with left-sided CDH (CDH group), trachea-occluded left-sided CDH (CDH+TO group), non-CDH (non-CDH group), and normal fetuses (normal group) were compared.

RESULTS

The %MT was significantly increased in all sizes of arteries in CDH compared with non-CDH and normal groups (P < .01). Compared with the CDH group, the CDH+TO group had significantly reduced %MT in all sizes of arteries (P < .01), to values comparable or less than the non-CDH and normal groups. The %AT of the CDH group was significantly increased in larger arteries compared with non-CDH and normal control groups (P < .01). CDH+TO had significantly decreased %AT compared with CDH in both larger (P < .01), and smaller arteries (P < .05) and that was comparable with the non-CDH and normal control groups.

CONCLUSIONS

TO in hypoplastic CDH lung can reverse the pulmonary arterial structural changes that are seen in the nitrofen-induced fetal rat model of CDH. These data suggest that TO may reduce pulmonary vascular reactivity, and the risk of postnatal persistent pulmonary hypertension observed in human neonates with severe CDH. J Pediatr Surg 36:839-845.

BAPS prize-1999: Lung growth induced by prenatal tracheal occlusion and its modifying factors: a study in the rat model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Prenatal tracheal occlusion (TO) has been shown to accelerate lung growth in animal models and models of pulmonary hypoplasia. However, these models may not mimic early events in human congenital diaphragmatic hernia (CDH). The authors previously have developed a model of TO in the rat. The purpose of this study was to apply this technique to characterize TO-induced lung growth in the early onset nitrofen-induced model of CDH, and to address the clinically important questions of the effect of timing of TO and maternal infusion of terbutaline on TO-induced lung growth.

METHODS

Left-sided CDH was induced in the fetuses of time-dated pregnant Sprague-Dawley rats by feeding 100 mg of nitrofen on day 9 of gestation. TO was performed via maternal laparotomy and hysterotomy at 19 days' gestation. At harvest (21.5 days' gestation), lungs from nitrofen-exposed fetuses without CDH (non-CDH), with CDH (CDH), and with CDH and TO (CDH-TO) were compared by analysis of wet and dry weight, DNA and protein content, and stereologic morphometry. A second study was performed to assess relative lung growth achieved by equal intervals of TO after "early" (19 days) versus "late" (20 days) gestational TO. Finally, the effect of maternal infusion of terbutaline, a commonly used tocolytic for fetal surgery, on TO-induced lung growth was analyzed.

RESULTS

Analysis of lung growth showed consistent and significant lung growth in CDH-TO lungs. Lung growth after TO was proliferative and characterized by an increase in parenchymal volume as manifest by increased total saccular number and surface area and radial saccular count. Although visceral reduction was partially achieved, herniated liver was reduced incompletely. The majority of lung growth occurred during the latter half of the TO period. Early gestational age at TO and maternal terbutaline administration adversely influenced lung growth in CDH-TO fetuses.

CONCLUSIONS

Prenatal TO induces dramatic lung growth in the early onset, nitrofen-induced rat model of CDH. TO is more effective later in gestation presumably because of the advanced stage of lung development and lung fluid production. This effect could be counterbalanced by the use of beta-mimetic tocolytic, which inhibits fetal lung fluid production late in gestation. Multiple factors including fetal lung fluid production and absorption, pharmacologic agents, space-occupying herniated viscera, and timing and duration of TO may be important clinical variables. The development of the rat model should facilitate further studies into the cellular and molecular mechanisms responsible for TO-induced lung growth.

Treatment of severe congenital diaphragmatic hernia by fetal tracheal occlusion: clinical experience with fifteen cases

OBJECTIVE

Our purpose was to determine whether prenatal tracheal occlusion improves survival in a selected population of fetuses affected by severe congenital diaphragmatic hernia.

STUDY DESIGN

Fetuses with isolated congenital diaphragmatic hernia were selected as candidates for fetal intervention by specific criteria designed to predict a 90% mortality rate with conventional postnatal treatment.

RESULTS

Fifteen fetuses underwent tracheal occlusion with 5 survivors (33%). Two fetuses were lost to early preterm labor. In 13 mothers, postoperative gestation ranged from 19 to 68 days, with a mean duration of pregnancy after tracheal occlusion of 38 days. The 5 survivors were hospitalized for an average of 76 days. Despite dramatic lung growth in some fetuses after tracheal occlusion, intensive management was required, and most deaths were caused by respiratory insufficiency.

CONCLUSION

Prenatal tracheal occlusion can result in impressive lung growth in a subset of fetuses with severe congenital diaphragmatic hernia. However, survival remains compromised by pulmonary functional abnormality and the consequences of prematurity.

Requirements for fetal surgery: the diaphragmatic hernia model

Fetal surgery for congenital diaphragmatic hernia and other fetal conditions can only be considered if (1) the morbidity of antenatal intervention is acceptable, (2) the diagnosis of the condition can be made accurately, (3) the condition can be differentiated from other, non-surgical anomalies. In addition, (4) the natural evolution of the disease, if left untreated, should be predictable, and the condition should be lethal or severely debilitating, (5) there should not exist adequate postnatal treatment, and (6) the proposed in utero operation should be technically feasible. Open fetal surgery has proven too invasive to be justified for the treatment of diaphragmatic hernia, and progress in postnatal therapy (including ECMO) has dramatically improved the neonatal outcome in all but a severe subgroup of patients. Recently, advances in endoscopic fetal surgery (which appears to be less stressful for the fetus and the gravid uterus) and a new approach to accelerate fetal lung growth and maturation have renewed the feasibility of in utero intervention for diaphragmatic hernia.