Stricture formation is manifested by variable degrees of dysphagia, ranging from dysphagia to solids or semisolids to absolute dysphagia with drooling of saliva and repeated chest infections from aspiration secondary to spill over or tracheo-esophageal fistula (Figure. 1 and 2). Manifestations of respiratory tract affection may present with stridor, hoarseness of voice, dyspnea or tachypnea ^{[1, 2]}.

After the lapse of at least 3-4 weeks, dye study should be done carefully using water soluble non-irritant dye for the fear of aspiration and subsequent pneumonitis due to spill over or the presence of fistula. The study should be done under screen and the dye is given orally or injected slowly through a naso-esophageal tube with suction device ready beside the patient. It will provide a basic image before doing an intervention. The study will demonstrate the site, the number, the length and the diameter of the stricture and will show associated gastro esophageal reflux or pull up of the stomach by esophageal fibrosis causing hiatus hernia. Once the diagnosis of stricture is evident, the patient is scheduled for upper endoscopy after the lapse of at least 6 weeks from the initial injury. The data obtained from the contrast study should be correlated with that found on endoscopy ^{[3, 4]}. Some studies recommended doing endoscopy in the first 12-48 hours after the ingestion. Although it has the advantage of assessing the degree of affection and hence the possibility of future stricture formation, the risk of iatrogenic esophageal perforation is high. It is better to be done 6 weeks after the corrosive ingestion to minimize the risk of esophageal perforation. Endoscopic evaluation of the esophagus will confirm the contrast study findings and assess if the stricture if passable or not. It also has the advantage of being therapeutic at the same time (Figure. 3) ^{[5, 6]}.

Endoscopic dilatation is considered the cornerstone for management of caustic esophageal stricture.

Endoscopy in the acute phase

Early endoscopy may be of value as about 30% of patients with caustic ingestion may not have esophageal injury and can be discharged promptly. Endoscopy is usually done within 24-48 h after ingestion. However, some centers have recommended endoscopy as soon as possible ^{[7, 8]}. Initial endoscopy after 48 h of ingestion is not recommended as the injured esophagus may enter the phase of ulceration and granulation, in which the esophagus becomes fragile and easily perforated. Early endoscopy is beneficial to confirm the followings: existence of injury, degree of injury, and area of injury which could guide a treatment and predict a prognosis. Early endoscopy is contraindicated in patients with a suspicion of gastrointestinal perforation, necrosis of oral cavity and compromised airway. Gentle handling and avoidance of air over-insufflation is always recommended ^[9].

Endoscopy in the late phase

Endoscopy plays an important role in the treatment of caustic esophageal strictures. Caustic stricture is often complex and difficult to dilate ^[10]. Early esophageal dilatation can be done after 3 weeks of caustic ingestion. After 8 weeks, scar tissue is completely formed. Since good nutritional status is strongly related to a successful dilatation of an esophageal stricture, early feeding via gastrostomy should start as soon as patients are clinically stable, especially in those with a significant damage in the esophagus (Figure. 4) ^[11].

Practically, barium swallow is done at 2-4 weeks after caustic ingestion and dilatation starts at 6 weeks after ingestion. Barium swallow will provide crucial information on the stricture which could determine the safety and success of endoscopic dilatation. Esophageal dilatation can be done using various types of dilators. It can be performed under the combination of endoscopy and fluoroscopy or endoscopy alone ^[12].

Commonly used esophageal dilatators are:

1-Bougie dilator (Maloney-Hurst dilator):
This dilator has the advantage of being easy to use but it does not have a channel to insert a guide wire through it. So, it is suitable for short and straight strictures.
2-Wire-guided polyvinyl dilator (Savary-Gilliard dilator):
This dilator has a channel through which a guide wire can be passed under fluoroscopy followed by the appropriate dilator. It is suitable for tortuous, angulated and long strictures. Sensation of resistance during dilatation can be felt while using this dilator, thus resulting in protecting against over dilatation and esophageal perforation (Figure. 5).

3-Through-the-scope balloon dilator (CRE balloon dilator):
This instrument can be passed through the scope. It can reach an area which cannot be accessed by other dilators. However, resistance cannot be felt if over dilatation was done. Dilatation achieved by balloon dilators is through a radial force while other dilators make their action by both radial and longitudinal forces. Although the mechanisms by which dilatation is achieved are different, all dilators have comparable success rates and rate of perforation between 0.1%-0.4% (Figure. 6) ^[13].

Fluoroscopically guided esophageal balloon dilatation (EBD) offers numerous advantages over endoscopically guided EBD, particularly it provides superior image control and allows visualization of the esophageal stricture (ES) in its entirety (location, severity, length, rigidity, and shape). In the literature, the success rates for fluoroscopically guided EBD in children ranged from 64% to 100% ^[14].
EBD can cause external compression of the trachea or obstruction at the endotracheal tube tip. Thus, the surgical team should be aware of obstruction of the airway that may occur during maximal inflation of the balloon. The other disadvantage of EBD is its higher cost compared to that of the other dilators. Although the main complication of EBD is esophageal perforation, the risk is relatively low (0%–31%). The mortality rate in the previous decade was close to zero; however, it must be diagnosed earlier ^[15].

Various with dilatation are advocated to improve the outcome:

Electrocision
Electro cautery could be applied to a caustic stricture. In this technique, a needle knife is passed through a working channel of the endoscope to make multiple longitudinal incisions until the rim of the stricture disappears. This technique proved to be a useful adjunct in esophageal dilatation.
Intralesional steroid injection
In this method and before esophageal dilatation, triamcinolone acetonide (40 mg/ml) is used. 1 mL is diluted to 2-4 mL and injected at the stricture site in 4 quadrants. Combination of steroid injection and dilatation can achieve better dilatation, improve dysphagia and reduce dilatation sessions ^[16].
In our practice, upper endoscopy is usually done under general anesthesia using a flexible one. The size varies according to the age of the patients, but in the majority number 9 F is suitable to complete the procedure. The scope should be introduced gently under direct vision and mounted by an injection needle connected to a syringe containing 4 ml of diluted 1:1 triamcinolone acetonide. Once the site of stricture is seen, 4 quadrant injection of the stricture is performed avoiding injection at the level of the aortic arch for fear of hemorrhage. The needle is withdrawn, and a metal guidewire is introduced to negotiate the stricture till it can be felt over the epigastrium. Then the scope is withdrawn and a suitable size Savary dilator is passed over the introduced guidewire and pushed with utmost care till felt in the stomach over the epigastrium. Three successive sizes are used in the same session depending on the response of the stricture to dilatation.
Failure of passage of the guidewire will end the procedure to be repeated after 2 weeks, and in most cases the guidewire can pass to complete the dilatation procedure. In the presence of a multiple-level stricture, the first one is injected and partial introduction of the dilator over the guidewire will help to dilate the uppermost one followed by repeated sessions to complete the dilatation of the strictures at different levels. With around 30 new cases of caustic esophageal stricture presented to our department per year, studies we conducted found that, success rate of dilatation increased from 32% with dilatation only to 75% with roids injection and 70% with mitomycin application prior to dilatation, so we don’t perform dilatation without either steroids injection or mitomycin application.
Mitomycin-C injection and application
Injection or application of mitomycin-C into the stricture site was shown to improve dysphagia score and allow easy passage of dilators, because of mitomycin-C inhibited fibroblast proliferation and scar formation without interfering with wound healing ^[17]. A randomized controlled trial done in our department showed a reduction in dilatation sessions if applying mitomycin-C during esophageal dilatation ^[18].
Esophageal stent
Caustic esophageal strictures which are resistant to dilatation can be managed with insertion of esophageal stents. Self-expandable plastic stent (SEPS), fully-covered self-expandable metallic stent (FCSEMS) and recently, biodegradable (BD) stent can be used. In practice, SEPS and FCSEMS can be kept in place for 6 weeks but should be removed before 12 weeks. All types of esophageal stents have comparable efficacy, but biodegradable stents have an advantage in avoiding the need for removal. The success rate of stent application in caustic esophageal stricture was 33% with a migration rate of 40% ^[19].
Since its clinical success is about one-third and not long lasting, efficacy is limited and the short-term radial force applied by BD stents is inadequate to provide long term relief in such patients. Esophageal stent is considered as a last resource in the treatment of caustic esophageal injury ^[20].

The role of endoscopy in the long term follow up:

Since caustic injury of the esophagus has been associated with 1000-fold increased risk of esophageal carcinoma, patients with high grades injury should undergo endoscopic surveillance ^[21]. The incidence of caustic stricure associated esophageal cancer ranged between 0%-30% and bypass surgery seems to have no effect on development of cancer. The time between occurrence of caustic injury and malignant transformation of the esophagus was found to be several decades ^[22]. As a result, endoscopic surveillance of the injured esophagus should start at about 15-20 years after occurrence of caustic injury and it should be done every 2 or 3 years ^[23].

It should be reserved for strictures which are resistant to multiple sessions of endoscopic dilatation. Due to the high success rates of dilatation with the new modifications in our center, the necessity of esophageal replacement surgery for caustic stricture decreased from around 36 cases to 6 cases per year in the last four years. More than ten years ago, we were performing replacement surgery if patient is still having dysphagia after three sessions of dilatation, now this concept has changed too much. We are exhausting all possible ways to keep the native esophagus and we only consider replacement for cases with persistent non-dilatable strictures or cases who required repeated sessions (more than 20) with no improvement in the spacing for a long period of time (more than 2 years). The ideal esophageal substitute should have good blood supply, grow with the child and do not compromise the cardiac and respiratory functions. The surgical technique should be simple, safe and adaptable to the small children.

The most commonly done operations for esophageal replacement are:

Colon interposition
It was first described by Kelling and Vulliet in 1911. It is the most commonly done procedure for esophageal replacement. The right (ascending-transverse) or the left (transverse-descending) colon may be used. The conduit can be passed from the abdomen to be anastomosed to the cervical esophagus through a subcutaneous, a retrosternal or a transhiatal route, with the retrosternal being the most commonly used route. The most common postoperative complications are graft necrosis (0-14%) and cervical anastomosis leakage (6-28%) ^[24-26].
We routinely perform colon interposition as a way for esophageal replacement, as we found it’s the best way compared to other replacement surgeries. Through years, we made some modifications in the surgical technique which improved our outcome. We shifted from the transhiatal to the retrosternal route as it has fewer morbidities and mortalities with less operative time, better recovery and less hospital stay. It is better to take the graft with double blood supply and make it iso-peristaltic ^[27]. Antireflux can be made by simple suturing the colon graft to the lesser curvature of the stomach making an angle or by making the colo-gastric anastomosis in the posterior wall of the stomach, these techniques improved the reflux happening after colon interposition ^{[28, 29]}. On the long term follow up, no significant histopathological changes occurred in the colonic conduit (Figure. 7) ^[30].

Gastric tube
It was first described by Burrington and Stephens in 1968. A tube is created from the greater curvature of the stomach using a linear cutting gastro-intestinal anastomosis (GIA) stapler after division of the short gastric vessels. It can be also be passed from the abdomen to be anastomosed to the cervical esophagus through a retrosternal or a transhiatal route. The most common postoperative complications are leakage in the neck anastomosis (63%) and stricture in the tube (43%) ^{[31, 32]}.
Gastric transposition
It was first described by Prof. Lewis Spitz in 1981. The greater and lesser curvatures of the stomach are mobilized. It will be passed from the abdomen to be anastomosed to the cervical esophagus through the transhiatal route. The incidence of postoperative cervical anastomosis leakage is 12-36% and the incidence of anastomotic stricture is 20-49% ^{[33, 34]}.

Caustic esophageal strictures could be managed successfully with advanced techniques of endoscopic dilatation.