ESOPHAGEAL STRICTURES

Esophageal strictures occasionally occur in dogs and cats. Stricture usually occurs secondary to severe esophagitis that extends into deeper layers of the esophagus, inciting fibroblastic proliferation.

Anesthesia-related reflux is the most common cause of esophageal stricture. Stricture formation can occur after relatively short anesthetic proce­dures (e.g., for ovariohysterectomy), as well as after long procedures. It appears that prolonged anes­thesia, especially when followed by inability of a patient to resume sternal or upright posture, pro­motes gastroesophageal reflux that may persist even beyond the duration of the anesthesia, and thereby initiating and perpetuating to some degree the transition from severe esophagitis to stricture formation.

Clinical signs of dysphagia and regurgitation are usually evident by 5 to 14 days after the anesthetic episode. Occasionally, significant clinical signs are not evident until 4 to 6 weeks later. Variable degrees of luminal narrowing can occur, and in some patients the lumen diameter at the stricture site is extremely narrow (sometimes as small as 1 to 2 mm) (Figure 4-13). Stricture length also varies. Occasionally, one or two additional strictures will develop at other sites in the esophagus.

Clinical Signs

Clinical signs generally progress over 5 to 14 days after their onset. The predominant sign is regurgi­tation of solid food. In some patients there ini­tially is vomiting during the recovery phase after an anesthetic event that is followed by occa­sional vomiting over the ensuing several days. Regurgitation may then begin to occur. As a stric­ture worsens, only gruels can be successfully trans­ported to the stomach. In strictures associated with a very narrow luminal diameter (1 to 2 mm), only water is likely to be retained. Affected patients typ­ically remain active and alert and have excellent body condition. Signs of pain or discomfort are uncommon. The appetite is usually ravenous. Weight loss may occur over time as a result of decreased caloric intake associated with regurgita­tion.

Diagnosis

Esophageal strictures occur more commonly than many clinicians may recognize. A review of a patient's recent medical history is the first step in making an early diagnosis of esophageal stricture. Most patients with an esophageal stricture have undergone general anesthesia within the previous 2 to 3 weeks. Most patients that begin regurgitating shortly after an anesthetic event have an esophageal stricture. A recent history of frequent severe vom­iting in dogs or cats, onset of regurgitation associ-

FIGURE 4-12 Esophageal foreign body in a cat with subsequent development of esophageal stricture.

ated with administration of NSAIDs to dogs, doxy­cycline tablets to cats, or other medications, or recent vomiting of a large hairball by a cat also should heighten suspicion of esophageal stricture.

A diagnosis is established either by endoscopy or by barium contrast radiography using a swallow of barium and either static radiographs or fluo­roscopy (Figure 4-14). In some cases barium liquid mixed with food is required to demonstrate an esophageal stricture, since liquid barium may pass easily through a stricture without delineating its presence. Endoscopy allows evaluation of the appearance and pliability of the esophageal wall and luminal diameter. The endoscope is often too large to pass through the stricture area, so an assessment of stricture length often is not possible from direct examination alone. Stricture length can be assessed, however, by advancing endoscopic biopsy forceps through the stricture and then opening the cups once the instrument has been passed.

Esophageal neoplasia occasionally causes intra­mural stricture formation, and there usually is an appearance of mucosal irregularity and intralumi­nal mass effect. However, rarely a malignant stric­ture will appear benign with no intraluminal mass effect typical of neoplasia. If any uncertainty exists regarding the cause of a stricture (e.g., no recent

Figure 4-13 Severe cranial thoracic esophageal stricture in an 11-month-old cat that had been anesthetized 14 days before. There was a 5-day history of regurgitation that progressively worsened, resulting in referral for endoscopy. A, The extremely narrow esophageal lumen (approximately 1.5 mm) is visible just to the left of center. Note the white fibrous connective tissue around the lumen. Because the stricture was too narrow to attempt bougienage and balloon catheters had not yet been developed when this case was seen, stricture resection was performed through a right thoracotomy. Resection of 1.5 cm of esophagus was performed. B, Endoscopic examination 4 weeks after esophageal resection and anastomosis. Mild narrowing of the lumen remains, but the endoscope was easily advanced. Note the suture tags and the esophageal lumen beyond the anastomosis site. The cat was asymptomatic. (From Tams TR: Esophagoscopy. In Tams TR, ed: Small animal endoscopy, St.Louis, 1990, Mosby-Year Book.)

history of anesthesia to suggest a reflux episode), biopsies should be done to differentiate a truly benign stricture from a malignant one. Brushings for cytologic examination are useful for rapid assessment while one waits for biopsy results.

Treatment

Treatment options for benign esophageal stricture include surgical procedures such as resection and anastomosis or patch grafting, bougienage, and balloon catheter dilation. In humans laser therapy and prosthesis has also been utilized. The success rate in animals treated with surgical procedures has been reported as less than 50% and in those treated with bougienage techniques as 50% to 75%. Surgical resection may result in restricture at the site of the anastomosis. Balloon catheter dilation is much more successful than either surgery or bougienage. The advantages of this technique over bougienage include decreased risk of esophageal perforation, longer symptom-free periods between procedures, and a smaller total number of procedures required to resolve the problem.

Bougienage

A wide variety of esophageal dilation devices whose diameters increase in stepwise fashion are available, including mercury-filled bougies and Pilling bougies. Bougies have either rounded tips or tapered ends with bases that are wider than the tips. The narrow tip is advanced to the stricture site under endoscopic guidance, and the wider area of the bougie dilates the stricture as the bougie is advanced through it. Care must be exer­cised to ensure that the bougie tip is directed into the stricture opening and not too far lateral to it. There is risk of perforation if the latter occurs. Other dilators that can be used in selected cases include endotracheal tubes (for cervical esophageal strictures in small patients) and the flexible endo­scope itself.

The key to successful bougienage is to repeat the procedure as often as necessary to maintain improved luminal diameter. In many patients two to three bougienage procedures per week are nec­essary during the first several weeks of treatment before the desired effect is reached. After a stric-

Figure 4-14 Barium liquid contrast radiograph from a 5-month-old kitten that had been regurgitating for 2 months. At the time the kitten was seen at a referral center, it was regurgitating solid food immediately after eating. The kitten had been anesthetized and neutered at a shelter at approximately 8 to 9 weeks of age. Note the proximal esophageal dilation and the narrowing of the dye column just caudal to the heart. Esophagoscopy confirmed a diagnosis of esophageal stricture, related to an internal fibrous band (i.e., there was no appearance of a narrowing due to external compression). Because of the kitten’s poor body condition at the time of presentation at the referral center, a gastrostomy tube was placed surgically so that nutritional support could be provided immediately. The esophageal stricture was managed successfully through a total of four ballooning procedures performed under endoscopic guidance. At 2 years of age there had been no stricture recurrence, and the cat continues to do quite well. (Courtesy Dr. Susan Hackner.)

ture has been forced open, the natural tendency is for it to narrow again as collagen is formed during epithelial healing.

Balloon Catheter Dilation

Balloon catheter dilation produces results superior to bougienage techniques. Advantages include a minimal chance of esophageal perforation, the ability to visualize more adequately the stricture dilation as the procedure progresses, and longer stricture-free intervals.A major advantage to bal­loon dilation is that it produces a radial stretch force rather than a longitudinal shearing force, as occurs with bougienage (Figure 4-15). In many patients only two to four balloon dilation proce­dures are required.

Balloon catheters are available commercially (Microvasive/Boston Scientific, Natick, MA 01760). The catheter is constructed of polyethylene, and

Figure 4-15 A diagrammatic representation of the shearing forces associated with bougienage compared with the radial forces associated with balloon dilation. (From Dawson SI et al.: Severe esophageal strictures: indications for balloon catheter dilation. Radiology 153:631,1984.)

the balloon consists of a specially treated polyeth­ylene located peripheral to the central tubing.There is a radiopaque visible metal band at each end of the balloon. Various size balloons are available. A full set of balloons for use in animals would include bal­loons of the following inflated diameters: 6, 8, 10, 12, 15, and 20 mm. 25 and 30 mm—diameter balloon catheters are available for use in large dogs.

Smaller balloon dilators can be passed through the instrument channel of an endoscope with a 2.6-mm or larger instrument channel. However, since pediatric size human and veterinary use flex­ible endoscopes have a channel size of 2.0 to 2.5 mm, most procedures are done in animals by pass­ing the balloon dilator alongside the endoscope. The balloon can be inflated with dilute iodinated contrast material or water. With the patient under general anesthesia, the catheter is advanced under endoscopic guidance and positioned with the mid­dle part of the catheter centered in the stricture. During the first procedure a lateral thoracic ra­diograph is usually made, especially in situations in which the stricture site is very narrow, to confirm whether or not the balloon positioning is correct. If fluoroscopy is used, the stricture and its response as the balloon is dilated can be observed directly. The stricture is apparent as a narrowing or waist in the balloon. Fluoroscopy is certainly not necessary to perform the procedure safely, however, and in most cases it is not used.

Once positioned, the balloon is distended with water or dilute contrast medium, and the luminal pressure is monitored with the pressure gauge. This increased pressure is associated with effacement of the waist, indicating dilation of the stricture (Figure 4-16).A dilation time of 2 to 4 minutes at 40 to 45 psi seems to be adequate for stricture dilation in dogs and cats (initially a time of 2 minutes is used so that initial response can be determined). After dilation, the balloon is deflated and the catheter removed. Immediate postdilation endoscopy is recommended to ensure resolution of the stricture. Dilation periods of 4 minutes are usually used in cases in which frequent procedures have not yet successfully solved the problem.

Mild to moderate hemorrhage around the stricture site is a normal postdilation finding. If there is no hemorrhage, the stricture was not dilated to any significant degree. With a very aggressive dilation, long and fairly deep longitudi­nal splits may occur in the esophageal wall. It is generally best to act a little conservatively during initial dilation procedures so as to minimize the likelihood of perforation that could result from using too large a balloon. Usually 2 to 3 progres­sively larger balloons are used in sequence during each individual anesthesia. Because esophageal stric­tures tend to close down again fairly quickly after being dilated, two to three individual dilation procedures are routinely scheduled during the first 7 days. Subsequent procedures are scheduled based on patient response dur­ing the first 1 to 2 weeks.

Factors that help determine the number of bal­loon dilation procedures that will be necessary

FIGURE 4-16 Radiographic appearance of a balloon catheter during an esophageal stricture dilation procedure. A, The balloon catheter is advanced under endoscopic guidance. The stricture is located over the base of the heart. The catheter’s soft, flexible radiopaque guide tip is visible in the stomach and distal esophagus. The radiopaque wire in the catheter shaft is clearly visible in the cranial and middle thorax. B, A fully distended balloon catheter with a diameter of 20 mm. The stricture has been fully dilated.

include severity and length of the stricture, num­ber of strictures, and the ease of the initial stricture dilation. In general, tight strictures and those that were several millimeters long require more dila­tions than those of moderate severity and shorter length. Patients with multiple strictures tend to require more dilations than those with single stric­tures.

A stricture that has been present for longer than several months may become so fibrotic that it may not be possible to dilate the stricture with bal­loons. Therefore, once the presence of a stricture is confirmed, proper treatment should be insti­tuted. A case in which an attempt to dilate a cervi­cal esophageal stricture was not made until 9 months after it was diagnosed is illustrated in Figure 4-17. Surgery was required to remove the stricture.

After bougienage or balloon dilation is begun, intensive therapy for esophagitis is instituted. This includes ^-receptor antagonist therapy, metoclo­pramide, sucralfate suspension, and prednisone (0.25 to 0.5 mg/lb/day). Food, usually chopped canned consistency, is usually resumed later on the same day or on the following day. If there is severe esophageal damage, it might be necessary to place a gastrostomy tube so that adequate nutritional support can be given. Most patients eat well very soon after a dilation procedure, even if there is sig­nificant esophageal mucosal tearing.

Prednisone is used to decrease fibroblastic activity. Whether or not it really helps to decrease or prevent further stricture formation is contro­versial. I have observed patients in which an esophageal stricture developed despite aggressive therapy (famotidine, sucralfate, metoclopramide, and prednisone) for acute moderate to severe esophagitis that was diagnosed early in its course via endoscopy. This therapeutic regimen is given both to treat the existing esophagitis and, it is hoped, to decrease the likelihood of stricture for­mation. Unfortunately, this approach does not always work. Some specialists have begun to take the additional step of injecting intralesional triam­cinolone with a Wang needle, under endoscopic guidance, after dilating severe esophageal strictures in an effort to further decrease fibroblastic activity. Endoscopy guided laser treatment used as an adjunct to ballooning is also being investigated.

It is emphasized that careful surveillance for development of a stricture is warranted in animals that are most at risk (e.g., those with anesthesia- related esophagitis and those that have recently vomited a large hairball). Esophagoscopy is the ideal procedure to monitor for progression or regression of esophagitis. Clinicians must recognize that once severe esophagitis is present, a stricture can form very rapidly.

The prognosis for resolution of an esophageal stricture disorder is excellent when balloon dila­tion is used. Sometimes mild permanent narrow­ing remains at the stricture site, but this is usually clinically insignificant. Cats and small dogs can manage well with an esophageal diameter of 1 cm or less if food consistency is limited to soft meals. A diameter of 1 to 1.5 cm is necessary in medium to large dogs. Many patients are eventually able to eat foods of normal consistency.