Histopathologic study of esophageal atresia and tracheoesophageal fistula in an animal model

H-type congenital tracheoesophageal fistula: Insights from 70 years of The Royal Children's Hospital experience

BACKGROUND

The long-term outcomes of H-type tracheoesophageal fistula (TOF), an uncommon variant of esophageal atresia/tracheoesophageal fistula (OA/TOF), are rarely described in the literature. We reviewed our institutional experience of 70 years.

METHODS

The Nate Myers Oesophageal Atresia Database was queried for patients with an H-type TOF (1948-2017). Data included presentation, diagnostic workup, surgical management, and outcomes.

RESULTS

Of 1088 patients with OA/TOF, 56 (5.1%) had an H-type TOF. The most common presenting symptoms were cyanotic episodes (68%), choking with feeds (52%), and aspiration pneumonitis (46%). The majority (82%) were symptomatic in the first week of life. Coexisting congenital anomalies were present in 46%: cardiac (13/56, 23%), genitourinary (10/56, 18%), and vertebral/skeletal (9/56, 16%). Patients were consistently diagnosed with prone contrast tube esophagogram (77% sensitivity on the first study and 96% after a second study). The fistula was most commonly approached through a right cervical collar incision. Right vocal cord palsy occurred in 22%, with one case of bilateral palsies. Other complications included leak (5.6%), recurrence (9.3%), stricture (1.9%), and diverticulum (1.9%). Although there was a trend towards a lower recurrence rate when interposition material was used, this was not statistically significant (3.3% vs 16.7%, p = 0.16). Survival in operative cases was 98.2%, and when all diagnosed cases were considered was 89.3%.

CONCLUSIONS

We have reported the largest single-center series of H-type TOF. Diagnosis is challenging, and surgical morbidity remains high. Despite this, long-term outcomes are favorable.

LEVEL OF EVIDENCE

IV.

Esophageal duplication and congenital esophageal stenosis

Esophageal duplication and congenital esophageal stenosis (CES) may represent diseases with common embryologic etiologies, namely, faulty tracheoesophageal separation and differentiation. Here, we will re-enforce definitions for these diseases as well as review their embryology, diagnosis, and treatment.

Adriamycin-Induced Models of VACTERL Association

Animal models are of great importance for medical research. They have enabled analysis of the aetiology and pathogenesis of complex congenital malformations and have also led to major advances in the surgical and therapeutic management of these conditions. Animal models allow us to comprehend the morphological and molecular basis of disease and consequently to discover novel approaches for both surgical and medical therapy. The anthracycline antibiotic adriamycin was incidentally found to have teratogenic effects on rats, producing a range of defects remarkably similar to the VACTERL association of congenital anomalies in humans, providing a reproducible animal model of this condition. VACTERL association is a spectrum of birth defects which includes vertebral, anal, cardiovascular, tracheo-oesophageal, renal and limb anomalies. In recent years, adriamycin rodent models of VACTERL have provided valuable insights into the pathogenesis of this complex association, particularly in relation to tracheo-oesophageal malformations. The adriamycin rat model and adriamycin mouse model are now well established in the investigation of the morphology of faulty organogenesis and the regulation of gene expression in tracheo-oesophageal anomalies.

Laryngo-tracheo-oesophageal clefts

A laryngo-tracheo-esophageal cleft (LC) is a congenital malformation characterized by an abnormal, posterior, sagittal communication between the larynx and the pharynx, possibly extending downward between the trachea and the esophagus. The estimated annual incidence of LC is 1/10,000 to 1/20,000 live births, accounting for 0.2% to 1.5% of congenital malformations of the larynx. These incidence rates may however be underestimated due to difficulty in diagnosing minor forms and a high mortality rate in severe forms. A slightly higher incidence has been reported in boys than in girls. No specific geographic distribution has been found. Depending on the severity of the malformation, patients may present with stridor, hoarse cry, swallowing difficulties, aspirations, cough, dyspnea and cyanosis through to early respiratory distress. Five types of laryngo-tracheo-esophageal cleft have been described based on the downward extension of the cleft, which typically correlates with the severity of symptoms: Type 0 laryngo-tracheo-esophageal cleft to Type 4 laryngo-tracheo-esophageal cleft. LC is often associated with other congenital abnormalities/anomalies (16% to 68%), mainly involving the gastro-intestinal tract, which include laryngomalacia, tracheo-bronchial dyskinesia, tracheo-bronchomalacia (mostly in types 3 and 4), and gastro-esophageal reflux disease (GERD). The syndromes most frequently associated with an LC are Opitz/BBB syndrome, Pallister Hall syndrome, VACTERL/VATER association, and CHARGE syndrome. Laryngeal clefts result from failure of fusion of the posterior cricoid lamina and abnormal development of the tracheo-esophageal septum. The causes of the embryological developmental anomalies leading to LC are not known but are thought to be multifactorial. LC appears to be mostly sporadic although some familial cases with suspected autosomal dominant transmission have been reported. The age of diagnosis depends mainly on the severity of the clinical symptoms and therefore on the extent of the LC. Diagnosis is made either based on clinical manifestations or on investigations, such as endoscopy, X-ray, CT scan, performed for other conditions. Differential diagnoses include tracheo-bronchial fistula, gastro-esophageal reflux disease and neurological swallowing disorders, as well as laryngomalacia and laryngeal palsy. Prenatal diagnosis of LC has never been reported, although associated anomalies may be detected on fetal ultrasonography. Once the cleft is diagnosed, it is essential to determine its length to orient the management and treatment approach. Management involves maintenance of satisfactory ventilation, prevention of secondary pulmonary complications as a result of repeated aspirations, and adequate feeding. Endotracheal intubation may be required for respiratory distress in severe cases. Treatment requires endoscopic or external surgery to close the cleft. Surgery should be performed as early as possible to avoid complications related to aspiration and gastric reflux, except in type 0 and type 1 cases in which conservative measures must first be attempted. The prognosis is variable depending on the severity of the LC and associated malformations. Early diagnosis and appropriate treatment and management help to reduce mortality and morbidity.

Congenital anomalies of the esophagus

Congenital malformations of the esophagus are frequently encountered by pediatric surgeons, especially esophageal atresia with or without tracheo-esophageal fistula. However, the molecular mechanisms underlying the development of these various anomalies are not clear. Here we present a brief overview of the embryologic development of the tracheoesophageal tube, along with some of the genetic controls which, when defective can lead to abnormal separation of this tube.

Intramural ganglion structures in esophageal atresia: a morphologic and immunohistochemical study

Introduction and Aim. Disorders of esophageal motility causing dysphagia and gastroesophageal reflux are frequent in survivors to esophageal atresia (EA) and distal tracheoesophageal fistula (TEF). The aim of the present study was to investigate the histologic and immunohistochemical features in both esophageal atretic segments to further understand the nature of the motor disorders observed in these patients. Material and Methods. Esophageal specimens from 12 newborns with EA/TEF and 5 newborns dead of unrelated causes were examined. The specimens were fixed in 5% buffered formalin, included in paraffin and cut in 5 micron sections that were stained with hematoxilin and eosin (H and E), and immunohistochemical stainings for Actin, S-100 protein, Neurofilament, Neuron-Specific-Enolase, Chromogranin A and Peripherin were evaluated under the microscope. Results. In controls, the distribution of the neural elements was rather homogenous at both levels of the esophagus. In contrast, the atretic segments showed quantitative and qualitative differences between them with sparser nervous tissue in the distal one in comparison with the proximal one and with controls. Conclusions. These results further support the assumption that histomorphological alterations of the muscular and nervous elements within the esophageal wall might contribute to esophageal dysmotility in patients surviving neonatal operations for EA/TEF.

Intrinsic esophageal innervation in esophageal atresia without fistula

Esophageal atresia and tracheo-esophageal fistula (EA + TEF) are often associated with malformations of neural crest origin. Esophageal innervation is also derived from the neural crest and it is abnormal in EA + TEF in which there is motor dysfunction. Our aim was to examine the intrinsic esophageal innervation in children with isolated EA in which different embryogenic mechanisms might be involved. Specimens from the proximal and distal esophageal segments of 6/35 patients who had esophageal replacement for isolated EA between 1965 and 2006 were suitable for the study. They were sectioned and immunostained with anti-neurofilament (NF) and anti-S-100 antibodies. The muscle and neural surfaces on each section were measured with the assistance of image processing software. The surface of the ganglia and the number of neurons per ganglion were determined at high power microscopy. The findings were compared with those of six autopsy specimens from newborns dead of other diseases by means of standard statistical tests and a significance threshold of P < 0.05. Unmatched age/size of babies in isolated EA and control groups precluded comparison of the relative surfaces occupied by neural elements. Patients with pure EA had denser fibrilar network and larger ganglia than controls. The number of neurons/ganglion were similar in both groups although the cells from EA patients were larger. The findings were similar at both esophageal levels studied. In spite of methodologic biases, it seems that intrinsic esophageal fibrilar network is denser and the intramural ganglia larger with larger cells in patients with pure EA than in controls on both esophageal ends of the organ. These neural anomalies are only in part reminiscent of those described in regular EA/TEF but may as well explain esophageal dysfunction in patients with repaired isolated EA.

Congenital esophageal stenosis associated with esophageal atresia: new concepts

Congenital esophageal stenosis (CES) is suspected by a fixed intrinsic narrowing of the esophagus that affects the normal swallowing mechanism. The diagnosis is only confirmed by histopathologic picture, which may show fibromuscular disease (FMD) or tracheobronchial remnants (TBR). The latter involves ciliated pseudo stratified columnar epithelium, seromucous glands or cartilage each alone or in combination. The aim of this study is to document the usefulness of histologic picture of surgical specimens obtained from the lower esophageal pouch (LEP) during primary repair in detecting cases of CES associated with esophageal atresia (EA) with or without tracheoesophageal fistula (TEF). Over an 8-year period, 57 consecutive cases operated upon for EA with or without TEF were subjected for histologic examination of surgical specimens obtained from the tip of the LEP. Cases that histologically showed FMD or TBR were included. The usefulness of this histologic picture as a diagnostic and therapeutic aid is assessed. Methods of treatment and outcome were also reviewed. Eight patients out of 57 (14%) had a histologic picture suggestive of CES, two with FMD, four with TBR without cartilage and two with cartilage. Out of 57 patients, 23 developed strictures, six of them had positive biopsies suggestive of CES. One patient with TBR without cartilage did not have stricture. Another case of pure atresia had LEP resection and gastric pull up showed cartilage involving the whole lower esophagus. Excluding the case of pure EA with gastric pull up, all patients suffered from feeding problems and recurrent aspiration. Fluoroscopic barium studies showed late onset minor dysmotility in five patients and late onset major dysmotility in two. All cases studied showed significant gastro-esophageal reflux (GER). Stricture was seen at the anastomotic site extending distally in the two fibromuscular cases and one case with cartilage, at the anastomotic site in three cases with TBR without cartilage. Anti reflux surgical procedures were performed in four patients without benefit in two patients with major dysmotility. Dilatation was successful in the three patients with TBR without cartilage. One patient with cartilage had resection of the anastomotic site and required frequent dilatations and is now doing well. A case of FMD did not improve after frequent dilatations and myotomy together with Nissen's fundoplication and required resection while the other case of FMD responded partially to dilatations. Cartilage in cases of CES requires surgical resection. Those with TBR without cartilage may not develop stricture. If stricture develops, it responds well to dilatation and patients have good clinical outcomes. Unlike isolated CES, GER is a significant feature in CES with EA. Anti reflux procedures should be avoided before definitive surgery for the stricture and if necessary a partial wrap with gastrostomy is recommended. CES should be considered in the etiology of anastomotic stricture. Taking a surgical specimen routinely from the tip of the LEP during primary esophageal repair for histologic studies is highly recommended.

Stephen L. Gans Distinguished Overseas Lecture. The neural crest in pediatric surgery

AIM

This review highlights the relevance of the neural crest (NC) as a developmental control mechanism involved in several pediatric surgical conditions and the investigative interest of following some of its known signaling pathways.

METHODS

The participation of the NC in facial clefts, ear defects, branchial fistulae and cysts, heart outflow tract and aortic arch anomalies, pigmentary disorders, abnormal enteric innervation, neural tumors, hemangiomas, and vascular anomalies is briefly reviewed. Then, the literature on clinical and experimental esophageal atresia-tracheoesophageal fistula (EA-TEF) and congenital diaphragmatic hernia (CDH) is reviewed for the presence of associated NC defects. Finally, some of the molecular signaling pathways involved in both conditions (sonic hedgehog, Hox genes, and retinoids) are summarized.

RESULTS

The association of facial, cardiovascular, thymic, parathyroid, and C-cell defects together with anomalies of extrinsic and intrinsic esophageal innervation in babies and/or animals with both EA-TEF and CDH strongly supports the hypothesis that NC is involved in the pathogenesis of these malformative clusters. On the other hand, both EA-TEF and CDH are observed in mice mutant for genes involved in the previously mentioned signaling pathways.

CONCLUSIONS

The investigation of NC-related molecular pathogenic pathways involved in malformative associations like EA-TEF and CDH that are induced by chromosomal anomalies, chemical teratogens, and engineered mutations is a promising way of clarifying why and how some pediatric surgical conditions occur. Pediatric surgeons should be actively involved in these investigations.

Faulty bone morphogenetic protein signaling in esophageal atresia with tracheoesophageal fistula

BACKGROUND

The organogenesis of esophageal atresia with tracheoesophageal fistula remains unclear. We have previously demonstrated that the fistula tract develops from a trifurcation of the embryonic lung bud and displays pulmonary lineage traits. Unlike the lung, the fistula grows without branching. Bone morphogenetic proteins (BMPs) are known to be important in lung branching. We studied possible BMP signaling defects as a potential cause for the absence of branching in the fistula tract.

METHODS

Adriamycin was administered to pregnant rats on days 6-9 of gestation to induce tracheoesophageal fistula. Microdissection was performed at E13 and E17 isolating the foregut. Tissues were analyzed using immunohistochemistry for BMP ligand (BMP2, BMP4, BMP7) and receptor (BMPRIA, BMPRIB, BMPRII) expression.

RESULTS

Immunohistochemistry revealed the presence of all 3 BMP ligands at E13, localized specifically to the esophageal mucosa but absent in the fistula and lung. At E17, the ligands were again present in the esophageal mucosa, and additionally in the fistula tract mucosa, but remained absent in the lung. At E17, all of the BMP receptors were also localized to the luminal surface of esophagus and fistula. However, in the lung epithelium, only BMPRII was found, whereas BMPRIA and BMPRIB remained absent.

CONCLUSIONS

The normal expression pattern of BMP4 was increased at the branch tips and low between branches. Among other results, we show here a constant expression level of BMP ligands throughout the entire epithelium of the fistula tract. This diffuse expression suggests defective BMP signaling in the fistula tract and explains its nonbranching phenotype.

Bone morphogenetic protein expression patterns in human esophageal atresia with tracheoesophageal fistula

The organogenesis of esophageal atresia with tracheoesophageal fistula (EA/TEF) remains unknown. The fistula tract appears to develop from a non-branching trifurcation of the embryonic lung bud. The non-branching growth of the fistula differs from the other lung buds and suggests a deficiency in bone morphogenetic protein (BMP) signaling, since BMPs are critical to proper lung development and branching. With IRB approval, portions of newborn human proximal esophageal pouch and distal fistula samples were recovered at the time of surgical repair of EA/TEF. The tissues were processed for immunohistochemistry. Commercially available fetal tissues were used as controls. In control tissues, BMP ligands (BMP 2, 4, and 7) were all present in the esophagus but absent in the trachea. BMPRIA was absent in both tissues. BMPRIB was detected in trachea but not in esophagus and BMPRII was detected in esophagus but not in trachea. In the EA/TEF specimens, all BMP ligands were present in the proximal esophageal pouch but absent in the fistula tract. BMPRIA and BMPRIB were not detected in either tissue. However, BMPRII was found in both fistula tract and proximal pouch. The submucosa of the fistula appears to maintain a mixed (identical neither to lung, esophagus, or trachea) BMP signaling pattern, providing one mechanism which could potentially explain the esophageal dismotility and lack of lung branching seen in the fistula/distal esophagus.

Histological and histochemical assessment of the effects of a single dose adriamycin on fetal rat kidney

Adriamycin (ADR) induces nephritic syndrome (NS) in adult rats. Therefore, effects of ADR in a single dose of 5mg/kg body weight given intraperitoneally to the mothers at 4 weeks before pregnancy were assessed on fetal rat kidneys in the present study. It induces increased amounts of PAS(+)-positive mesangial matrix, glomerulosclerosis, dilatation of the urinary space and thickening of basement membranes in glomeruli. In tubules, it damages or completely destroys epithelial cells, it induces dilatation of the tubular lumen and disintegration of the brush border. Changes in fetal rat kidney as observed light microscopically appeared to be similar to those described in kidneys of adult rats with NS induced by adriamycin, but were less distinct.

Complete discontinuity of the distal fistula tract from the developing gut: direct histologic evidence for the mechanism of tracheoesophageal fistula formation

The embryogenesis of tracheoesophageal anomalies remains controversial. The purpose of this study was to better define the embryogenesis of developing esophageal atresia with tracheoesophageal fistula (EA/TEF), with specific attention to the controversial issue of whether a discontinuity exists in the foregut during its development of EA/TEF. Pregnant outbred rats were injected with adriamycin (2 mg/kg i.p.) on days 6-9 of gestation (E6-E9). At E12.5 and 13.5, microdissection of the entire foregut was performed. Foreguts were examined by phase microscopy, and serial, precisely transverse sections were created for hematoxylin and eosin (H&E) staining. Gross microdissection of the developing foregut at E12.5 (n = 9) revealed a blind-ending, bulbous fistula tract arising from the middle branch of the tracheal trifurcation (as seen by direct and phase microscopy). No connection with the gut could be appreciated at E12.5, but by E13.5 (n = 10) there was an obvious connection between the fistula and the stomach. Serial H&E transverse sections also demonstrated a blind-ending fistula tract arising from the trachea at E12.5. This fistula tract was clearly discontinuous from the developing stomach, which appeared much further caudal to the end of the fistula tract. These results strongly support a model of experimental TEF wherein the fistula tract arises from a trifurcation of the trachea, and (only during a specific gestational window between days 12.5 and 13.5) there is discontinuity between the fistula tract and the stomach. By day 13.5, the fistula joins with the stomach anlage. These observations in the developing EA/TEF should help to resolve the controversy about the mechanism of EA/TEF formation.

Dorsoventral patterning in oesophageal atresia with tracheo-oesophageal fistula: Evidence from a new mouse model

BACKGROUND/PURPOSE

The well-established Adriamycin rat model of oesophageal atresia (OA) and tracheo-oesophageal fistula (TOF) complements recently described mouse genetic models in which loss of function mutations in foregut patterning genes, such as Nkx2.1 (Ttf 1), lead to OA/TOF. The authors aimed to integrate the 2 systems by adapting the Adriamycin model to the mouse to study molecular aspects of tracheo-oesophageal development.

METHODS

Pregnant CBA/Ca mice were injected intraperitoneally with 4 mg/kg of Adriamycin on embryonic days 7.5 and 8.5. Embryos and fetuses of various gestational ages were subjected to morphologic or histologic examination. Sections were stained with H & E or processed for immunohistochemistry using an antibody specific for Nkx2.1.

RESULTS

Tracheo-oesophageal malformations were observed in 47% of Adriamycin-treated embryos. Early foregut development was similar in Adriamycin-exposed and control embryos but, by E11.5, many treated embryos had an undivided oesophago-trachea, which gave rise to the lung buds and a fistula to the stomach. The fistula originated from the dorsal aspect of the undivided tube and was negative for Nkx2.1, or showed only transient Nkx2.1 expression, compared to the strongly positive bronchi ventrally.

CONCLUSIONS

The Adriamycin model of OA is adaptable to the mouse. In the absence of tracheo-oesophageal separation, the dorsal fistula retains its nonrespiratory commitment suggesting that dorsoventral patterning of foregut development is undisturbed by Adriamycin exposure.

Impaired esophageal reactivity in adriamycin-induced rat esophageal atresia: an in vitro study

PURPOSE

The aim of this study was to investigate the reactivity of lower esophageal smooth muscle in the Adriamycin-induced esophageal atresia (EA) rat model.

METHODS

The fetuses were divided into 3 groups. The control group was exposed to saline. The second group comprised fetuses that were exposed to Adriamycin but in whom EA did not develop. The third group comprised of fetuses that were exposed to Adriamycin and EA was observed. The reactivity of distal esophageal strips was studied in organ chambers.

RESULTS

The tension was similar in all groups precontracted with carbachol for the study of relaxation to serotonin. Relaxation of lower esophageal strips to serotonin was comparably unaffected in the control and Adriamycin-no EA groups, whereas it was significantly inhibited in the EA group with decreased E(max) and pD(2) values. Contractile responses of esophageal smooth muscle to carbachol or 80 mmol/L KCl and relaxant responses to papaverine were similar in all groups. No change in agonist potency was observed among the groups.

CONCLUSIONS

Our study showed impairment of serotonin-receptor-mediated relaxation; but not of cholinoceptor-mediated contraction of the lower esophageal smooth muscle in the EA. Thus, impaired relaxant responses may be, at least in part, a contributing factor in the esophageal dismotility seen in EA.

Teratogenic effects of Doxorubicin in rats at midgestation and at term

Doxorubicin (DOXO) is an anticancer drug widely used against leukaemias and solid tumours. Doxorubicin is teratogenic in laboratory species, as demonstrated by a number of in vivo and in vitro experiments. In our in vitro study, the endoderm of the primitive gut and the caudal mesenchymes have been the main target tissues, while oxidative stress has been excluded as a mechanism in Doxorubicin-related abnormalities. The aims of the present work are the confirmation of our previous in vitro results (obtained on rat embryos cultured from 9.5 to 11.5 d.p.c.) in an in vivo model (midgestation) and the comparison of the abnormalities observed in the embryos at midgestation with malformations observable at term of pregnancy. For this purpose, pregnant rats were i.p. treated on 9.5 and 10.5 d.p.c. with DOXO. Embryos were analysed on 11 d.p.c., while foetuses were externally and viscerally analysed on 20 d.p.c. (term of gestation). The data collected at midgestation confirm the specific embryotoxic effects (particularly to the primitive gut and the caudal mesenchyme) previously observed in vitro. The data collected at term show the endoderm derivatives (gastrointestinal apparatus and respiratory tract) as the primary target organs, supporting the idea that the teratogenic activity of Doxorubicin is mediated by specific toxic effects directed to the primitive gut.

Mechanisms for the development of esophageal atresia

BACKGROUND

There is no universally accepted theory to explain esophageal embryology and the abnormal development that produces esophageal atresia.

METHODS

The impact of Adriamycin administration on the pathogenesis of esophageal atresia was studied in the rat model of VATER association, from embryonic day (ED) 10 to ED 13.

RESULTS

Tissues in the ED10 Adriamycin-exposed embryos displayed less cell proliferation as shown by the reduced population of MIB-5-labelled cells. Cell apoptosis that is characteristic of the normal ED 12 lateral epithelial folds of the foregut (the prospective site of tracheoesophageal septation) was absent in the foregut of the Adriamycin-exposed embryo. Histologic examination of the ED 11-exposed embryo showed the presence of abnormal notochord that was stretched, split, or tethered to the foregut. This contrasts with the normal embryo in which the notochord was localized in close vicinity of the ventral part of the neural tube and separated from the foregut by ample amount of mesenchyme. The abnormal localization of the notochord was accompanied by the lack of down-regulation of the sonic hedgehog (Shh) activity in the prospective site of future tracheoesophageal separation in the exposed ED 12 embryo.

CONCLUSION

The authors proposed that the ectopic location of the notochord leads to the disruption in Shh signalling that may underpin the development of esophageal atresia.

Defective fibroblast growth factor signaling allows for nonbranching growth of the respiratory-derived fistula tract in esophageal atresia with tracheoesophageal fistula

BACKGROUND/PURPOSE

The fistula tract in esophageal atresia with tracheoesophageal fistula (EA-TEF) appears to arise from a trifurcation of the embryonic lung bud. Subsequently, it does not branch like the other bronchi, which also arise from the lung bud. Previous results have implied that aberrant mesenchymal-epithelial signaling in the developing foregut, possibly involving fibroblast growth factors, may allow for the nonbranching growth of the fistula, and the ultimate development of the fistula tract in TEF.

METHODS

Adriamycin injections into pregnant rat dams induced EA-TEF formation in rat embryos. Control and Adriamycin-exposed embryos were harvested on the 13th gestational day, and the developing foregut was isolated with microdissection. mRNA was isolated from the developing fistula tract, embryonic lung, and normal embryonic esophagus. Reverse transcription-polymerase chain reaction (RT-PCR) for the IIIb splice variant of the FGF2R receptor was performed. Foregut specimens also were processed for histologic analysis, and immunofluorescence for FGF1 was performed.

RESULTS

FGF2R-IIIb is specifically absent from the developing fistula tract in TEF, whereas it is present in the normal developing lung and esophagus. FGF1 also is uniquely absent from the developing fistula tract, but it is present in the normal lung mesenchyme.

CONCLUSIONS

FGF1, FGF7, and FGF10 are critical mesenchymal factors that mediate proliferation and branching morphogenesis by the developing respiratory epithelium. The absence of FGF2R-IIIb, the obligate common receptor for FGF7 and FGF10, from the fistula tract, and the absence of FGF1 in the fistula tract mesenchyme, collectively imply the absence of a specific FGF signaling pathway in the developing fistula tract. This absence of FGF signaling could explain the lack of branching by the developing fistula tract as it grows caudally in the abnormally developing embryo. Downregulation of these components of the FGF signaling pathways may allow for a patterned compensation by the embryo for the proximal foregut atresia in this anomaly. This compensation may then reestablish gastrointestinal continuity as the fistula tract connects to the developing stomach.

A histopathological study of esophageal atresia and tracheoesophageal fistula

BACKGROUND/PURPOSE

Histopathologic examination of the esophagus has not been reported often in esophageal atresia (EA) and tracheoesophageal fistula (TEF). Abnormal esophageal motility has been reported after successful repair of EA and TEF, although the exact etiology of this motility disorder remains unclear. Histological evaluation of the fistulous portion of the esophagus has been performed to document any abnormality that may be responsible for the abnormal motility.

METHODS

Histopathological study of fistulous segment of esophageal atresia and distal TEF was conducted on 65 patients, which included autopsy material from 3 patients in whom the entire esophagus was examined by serial section. Special stains were administered to each specimen to look for tracheobronchial remnants and the arrangement of muscle fibers. Clinical evaluation was performed in 27 patients who were available for review 6 months to 9 years after successful surgical treatment. These patients were categorized into 3 groups according to their clinical status.

RESULTS

These findings showed that the majority of these patients have tracheobronchial remnants in the esophagus in the form of abnormal mucous glands and ducts, abnormal mucin secretion, presence of cartilage, and a disorganized muscle coat.

CONCLUSIONS

The presence of abnormal mucous glands and abnormal mucin secretion has not been highlighted before. Although tracheobronchial remnants and a disorganized muscle coat are common findings in the fistulous portion of the esophagus, these may not reflect the structure of the remaining esophagus.

Relationship of the notochord to foregut development in the fetal rat model of esophageal atresia

BACKGROUND/PURPOSE

The notochord (Nt) is thought to act as a primary organizer for adjacent axial embryonic organs. The current study used the Adriamycin-induced fetal rat model of esophageal atresia and tracheoesophageal fistula (EA-TEF) to determine whether anomalies of the foregut (FG) were associated with an abnormal Nt.

METHODS

Eight experimental female Sprague-Dawley rats received intraperitoneal injection of Adriamycin (1.75 mg/kg) on gestational days 6 to 9 inclusive, and 4 control rats received saline injection only. Their embryos were harvested on gestational days 11, 12, 13, and 14. Embryos from each age subgroup were serially sectioned and stained with H&E. The FG and Nt were traced from the primitive pharynx to the level of the stomach.

RESULTS

By day 11, the Nt of control embryos had completely separated from the FG and was located immediately ventral to the neural tube. On gestational day 12, the Nt detached from the neural tube, and the trachea and esophagus were separating. On day 11, in the Adriamycin-treated embryos, the Nt was still attached to an FG that was narrowed or occluded. On day 12, the Nt remained adherent to the FG from the primitive pharynx to the level above the primitive respiratory buds, at which point it became thicker and branched sagittally, with the anterior branch contacting or merging with the FG. The FG usually loses its lumen or continuity when in contact with the Nt.

CONCLUSIONS

Exposure of rat embryos to Adriamycin leads to abnormal development of the Nt, including prolonged attachment to or fusion with the FG, and abnormal branching. Traction on the FG by the Nt produces occlusion of its lumen and may result in its complete interruption. Separation of the Nt from the FG would appear to be a prerequisite for the normal development of the FG into its derivatives: the esophagus and trachea.

TTF-1 and HNF-3beta in the developing tracheoesophageal fistula: further evidence for the respiratory origin of the distal esophagus'

PURPOSE

Using an established rat model of esophageal atresia with tracheoesophageal fistula (EA-TEF), the authors have studied the organogenesis of this congenital anomaly. The authors previously have proposed that the "distal esophagus" actually is of respiratory lineage. In this report this hypothesis is tested by examining the expression of two foregut patterning transcription factors, thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor-3beta (HNF-3beta), within the developing TEF.

METHODS

Pregnant Sprague-Dawley rats were injected with 2.2 mg/kg of Adriamycin intraperitoneally on days 6 to 9 of gestation. Using microdissection, the trachea, blind-ending esophagus, TEF, and stomach were isolated from embryos of various gestional ages. Immunohistochemistry was performed using polyclonal antibodies to TTF-1 and HNF-3beta.

RESULTS

TTF-1 is a homeodomain protein that previously has been shown to be expressed in the lung and trachea but not in the gastrointestinal tract, and which, when deleted in a developing lung, results in a mouse with no peripheral lung parenchyma. TTF-1 was expressed strongly in the lung, fistula, and distal esophagus, but not in the proximal esophagus. HNF-3beta is a forkhead transcription factor important in foregut patterning that binds and activates the TTF-1 promotor sequence. HNF-3beta was expressed globally in the fistula and lung as well as the esophagus.

CONCLUSIONS

The expression of the lung-specific transcription factor TTF-1 within the TEF strongly implies that the "distal esophagus" is a respiratory-derived structure and thus supports our theory of TEF organogenesis. The conservation of HNF-3beta expression both in the TEF as well as the normal developing trachea and esophagus suggests that global foregut patterning is intact in the formation of this anomaly, and the defect lies at the level of the respiratory versus gastrointestinal commitment.

Molecular approaches to understanding organogenesis

The elucidation of the molecular mechanisms of mammalian organogenesis is the foundation on which we can build an improved understanding of organ pathology and pathophysiology. This paper uses the lung and the pancreas as paradigms to demonstrate how advances in basic molecular developmental biology research has translated into new appreciation of, and even novel potential treatment strategies for, congenital anomalies and mature diseases of these organs.

Apoptosis in tracheoesophageal embryogenesis in rat embryos with or without adriamycin treatment

PURPOSE

The aim of this study was to determine whether apoptosis participates in separation of the foregut into trachea and esophagus and to evaluate the potential role of apoptosis in the development of esophageal atresia and tracheoesophageal fistula (EA + TEF) induced by Adriamycin.

METHODS

Timed-pregnant rats were injected daily with either saline or Adriamycin (2 mg/kg) intraperitoneally on days 6 to 9 of gestation. Paraffin sections were prepared from 31 experimental and 31 control embryos at days 12 and 13 of gestation. Condensed nuclei were identified on the paraffin sections using the TUNEL method. Apoptosis was quantified by counting the positively stained cell nuclei in transverse sections of embryos.

RESULTS

In day 12 control embryos the number of apoptotic nuclei in both lateral ridges of the foregut was high (15.67 +/- 1.38) but relatively low (4.17 +/- 0.80) in Adriamycin-treated embryos (P< .0001). In day 13 Adriamycin-treated embryos, the number of apoptotic nuclei in the region of the upper esophageal pouch was extremely high (23.78.5 +/- 2.20) compared with no detectable apoptotic nuclei in the control embryos.

CONCLUSIONS

Apoptosis is required for normal tracheoesophageal embryogenesis and may be an important mechanism to be involved in the embryological development of esophageal atresia and tracheoesophageal fistula.

Tracheobronchial malformations in experimental esophageal atresia

BACKGROUND

Malformations of the tracheobronchial tree may account for postoperative respiratory symptoms in patients with esophageal atresia (EA). This study examines the respiratory tract in fetal rats with EA induced by Adriamycin.

METHODS

Time-mated female rats were given either 2 mg/kg intraperitoneal Adriamycin on gestational days 8 and 9 (adria group, n = 6) or no treatment (control group, n = 2), and the fetuses were recovered on day 21. Laryngo-tracheo bronchial tree was studied after transparentation and alcian blue-alizarin red staining that depicts the cartilage in blue and make the surrounding tissues transparent.

RESULTS

There were no malformations in any of the 1 1 control animals studied. Conversely, 31 of 46 (67%) Adriamycin fetuses had EA with distal TEF. These had more tracheal rings than controls (32+/-2 v 26+/-1.5, P < .05) at the expense of those of the mainstem bronchi (3.2+/-1 v 6.6+/-1.1 in the right, P< .05 and 6.2+/-2.1 v 11+/-1.1 in the left, P < .05). There were tracheal stenoses in 16 pups with EA (some severe and five double), and all these had fragmented rings in the trachea or bronchi. In six cases there was an ectopic upper right bronchus, and 1 had a grossly abnormal larynx. The malformations in the 15 Adriamycin-exposed fetuses without EA were limited to some fragmented or mishaped rings.

CONCLUSIONS

Laryngo-tracheobronchial malformations entailing the whole length of the tract are very constant and severe in rats with EA and tracheoesophageal fistula and correspond to an abnormal development of the tracheobronchial anlage from the ventral foregut. Their nature and extent invite a careful investigation of the respiratory tracts in EA babies in whom they could be underscored.

Dose response relationship between adriamycin and birth defects in a rat model of VATER association

BACKGROUND/PURPOSE

The aim of this study was to reproduce the animal model of esophageal atresia and the VATER association. The purpose was a dose response analysis of Adriamycin teratogenicity in the rat and comparison of these anomalies with the human VATER association.

METHODS

Twenty time-mated Sprague-Dawley rats received intraperitoneal Adriamycin (dose range, 0 to 2.5 mg/kg/d) for 4 consecutive gestational days E6 to E9. The embryos were harvested on day E21, inspected, weighed, and dissected with a binocular dissecting microscope. Statistical analysis was performed with exact chi2.

RESULTS

Threshold doses of 1.25 and 1.5 mg/kg/d Adriamycin produced renal and gastrointestinal anomalies, respectively (exact chi2, P < .00001). In doses below 1.25 mg/kg/d Adriamycin, no anomalies were seen, and in above-threshold doses, the frequency of anomalies rose sharply as the dose increased. At 2.25 mg/kg/d of Adriamycin all embryos were abnormal, and Adriamycin at 2.5 mg/kg/d led to resorption of all embryos.

CONCLUSIONS

Adriamycin induced esophageal atresia, and VATER in the rat is a reproducible model that has many similarities to the VATER anomalies in the human. There is a relationship between dose and the frequency as well as severity of anomalies. Further studies of this model are likely to provide information relevant to the understanding of this human congenital disease.

Esophageal atresia with tracheoesophageal fistula: suggested mechanism in faulty organogenesis

BACKGROUND/PURPOSE

The organogenesis of esophageal atresia with tracheoesophageal fistula (EA-TEF) is unknown. Using an established model for EA-TEF in rats, the authors proposed to study this aberrancy of development in the hope of gaining insight into its mechanism of formation.

METHODS

Pregnant Sprague-Dawley rats were injected with 2.2 mg/kg of Adriamycin intraperitoneally on days 6 through 9 of gestation. Using microdissection, the trachea, blind-ending esophagus, TEF, and stomach were isolated from embryos of various gestional ages. The specimens were analyzed histologically with routine H&E staining.

RESULTS

The classic EA-TEF developed in the embryos, with proximal EA and distal TEF. As expected, the atresia formed as a blind-ending pouch, but the distal fistula began as an apparent equal trifurcation of the tracheal anlage into two mainstem bronchi and the fistula tract leading to the stomach. Histological analysis of the fistula tract showed respiratorylike pseudostratified columnar epithelium.

CONCLUSIONS

TEF develops as the middle branch of a tracheal trifurcation. EA-TEF occurs by a primary atresia of the esophagus. As a secondary phenomenon, the distal foregut anlage is switched toward the pulmonary phenotype. It trifurcates, and its middle branch grows caudally to fistulize into the stomach.

Embryogenesis of tracheal atresia

A spectrum of tracheo-esophageal anomalies has been described in an adriamycin-treated model with common features to the human pattern. Tracheal agenesis was part of this spectrum. It is a rare congenital anomaly that has not been described in embryos. Virgin timed-pregnant Sprague-Dawley rats were injected with adriamycin i.p. at a dose of 2 mg/Kg on days 6-9 of gestation (plug day = day 0). Fetuses were recovered at term and histologic assessment of tracheo-esophageal anomalies was made. Also, embryos were removed on different gestational days and the embryology of these defects was analysed. Two out of sixty-two fetuses and nine out of 180 embryos were identified with tracheal atresia. Type III tracheal atresia was seen in the full-term fetuses with a tracheo-esophageal fistula arising from the origin of the left main bronchus. Day 13 embryos did not show normal tracheal development; instead, the lung buds developed from the ventral aspect of the foregut which continued to the stomach as a lower esophageal segment. A blind ending pouch was seen on the ventral aspect of the upper part of the foregut. The embryogenesis of tracheal atresia was similar to that of esophageal atresia except that the blind upper foregut pouch developed ventrally rather than dorsally.

Embryology of esophageal atresia in the adriamycin rat model

PURPOSE

The aim of this study was to describe the dysmorphogenetic process leading to esophageal atresia and tracheoesophageal fistula (EA + TEF) in the recently developed Adriamycin model of the malformation.

METHODS

Time-mated pregnant rats were given either Adriamycin (1.75 mg/kg intraperitoneally) or saline on days 6 to 9 of gestation, and their embryos recovered on days 12, 12.5, and 13 were serially sectioned in the transversal plane and studied microscopically after H&E and PAS staining. The findings were compared with those of age-matched untreated embryos.

RESULTS

All untreated and saline embryos were normal, whereas 49% of Adriamycin embryos had foregut malformations. Tracheoesophageal separation was complete on day 12 in control embryos, whereas 9 of 10 Adriamycin-exposed embryos had a common esophagotrachea with low emergence of the bronchi at that stage. This pattern had evolved into that of a regular EA + TEF in all nine malformed embryos by day 13. On day 12.5, esophagotrachea was found in 6 of 13 and EA + TEF in 5 of 13 embryos. Two had less well-defined malformations.

CONCLUSIONS

Esophagotrachea equivalent to complete tracheoesophageal cleft is the first step leading to EA + TEF in this model. The full-blown malformation is finally acquired by partial loss of the posterior wall of the foregut, which tapers-off in the mediastinal mesenchyme and respiratory differentiation of the anterior wall down to the level of bronchial bifurcation, where it constitutes the fistula and the distal esophagus.

Relationship between esophageal atresia with tracheoesophageal fistula and vertebral anomalies in mammalian embryos

BACKGROUND/PURPOSE

The association of esophageal atresia with tracheoesophageal fistula and vertebral anomalies is well known, although the embryology of the combined defects has not yet been analysed. The present study describes the origin and development of esophageal atresia with tracheoesophageal fistula and vertebral anomalies in embryos using a rat model of VATER association produced by Adriamycin administration.

RESULTS

The lung buds were seen to develop from the laryngotracheal groove but the trachea failed to grow normally and the foregut overgrowth compensated for this failure. The trachea developed by trachealization of the foregut, which continued as a fistula to the lower esophageal segment. The notochord did not separate from the foregut at the correct time (before day 11 in rat embryos, Carnegie stage 11 in human embryos). Overgrowth of the foregut ventrally and caudally carried with it the attached notochord in the same direction leading to abnormal bending of this structure.

CONCLUSION

This irregularity of the notochord may be responsible for abnormal development of the vertebrae.

Timing and embryology of esophageal atresia and tracheo-esophageal fistula

BACKGROUND

The embryology of tracheo-esophageal anomalies is controversial. The development of an adriamycin-treated animal model has enabled improved understanding of the embryogenesis of these anomalies. Using this model, we aimed to describe the events leading to esophageal atresia and tracheo-esophageal fistula.

METHODS

Timed-pregnant Sprague-Dawley rats were injected daily with adriamycin intraperitoneally at a dose of 2 mg/Kg on days 6-9 of gestation. Histological sections were prepared from 96 experimental and 34 control rat embryos at 11-14 days gestation (plug day = day 0).

RESULTS

The tracheal bud failed to develop normally from the foregut, leaving the foregut to give origin to both bronchi and differentiate into the respiratory system, and then continue as a fistula to the lower esophageal segment. Dorsal pouching of the proximal foregut, which is seen clearly on day 13, is responsible for the development of the upper esophageal segment.

CONCLUSIONS

We conclude that failure of the tracheal bud to develop normally from the primitive foregut is the main event which leads to the tracheo-esophageal anomalies. As the proximal part of the primitive foregut develops primarily into a trachea rather than an esophagus, the anomaly of the esophagus could be described as agenesis instead of atresia.