Causes
Esophageal strictures are a relatively uncommon condition in small animals but they have been well documented. They can be divided in benign and malignant and, based upon their site of origin they are classified as intrinsic (intramural) and extrinsic (extramural). The most common form affecting the dog and cat is the intramural stricture that can be congenital or acquired. Congenital strictures are rare and can appear as stenotic rings or membranes at various levels in the esophageal wall. Acquired strictures occur secondary to injury or severe esophagitis of any etiology extending into the submucosa or the muscle layer of the esophageal wall. Healing by intramural fibrosis of these lesions leads to stricture formation. Most cases of esophageal stricture in dogs and cats occur from reflux esophagitis secondary to reflux of gastric acid and enzymes during general anesthesia or hiatal disease, and from passage and removal of esophageal or gastric foreign bodies. Abnormal healing of previous esophageal surgery is also a common condition of stricture formation in dogs and cats. Severe esophagitis resulting from persistent vomiting, vomiting of hairballs in cats and acids or alkali ingestion, penetrating lesions, granulomas caused by Spirocerca lupi parasite and neoplasia are other possible causes. Extramural strictures may be congenital or acquired as well, but the congenital forms are certainly the most common. The most frequent causes include vascular ring anomalies, abscess formation, thymic or lung masses, enlarged thoracic lymph nodes and neoplasia.
Clinical Signs
At outset, the predominant sign of esophageal stricture is regurgitation shortly after eating. The animal may be otherwise healthy and the appetite is maintained or ravenous. Generally, fluids are retained while solid food is regurgitated. Excessive salivation may be observed. With the progression of esophageal obstruction and inflammation, regurgitation and dysphagia worsen and the animal may develop anorexia and severe weight loss. At this stage of disease, regurgitation may not be related to eating because secondary esophageal distension cranial to the lesion can act as food reservoir. Fever, cough and dyspnea indicate that secondary aspiration pneumonia has developed.
Diagnosis
Diagnosis is quite easily established and is based primarily on a detailed clinical history, clinical signs, radiographic examination and endoscopy. Clinical signs usually occur 1-2 weeks after the onset of the primary cause (injury, onset of esophagitis, general anesthesia etc.). History may indicate signs related to the lesions caused by the migrating forms of Spirocerca lupi. Physical examination is usually unremarkable and the animal may be active and alert. Increased salivation may be noticed. Chronic or neoplastic strictures are usually associated with weight loss and malnutrition. In some cases, severe signs of aspiration pneumonia can divert the attention of the clinician from the primary problem. Survey radiographs are often irrelevant in fibrosing strictures unless the esophagus is distended with food, fluids or air proximal to the stricture. Barium contrast radiography using barium liquid or barium mixed with food is usually diagnostic of an esophageal stricture, showing its location and length. Endoscopy allows evaluation of luminal diameter, morphology and nature (by cytology and/or biopsy) of the stricture, and the assessment of surrounding mucosa involvement. By endoscopy, a benign stricture may appear as a white ring of fibrous tissue narrowing the esophageal lumen at various degrees and not distending in response to air inflation. Benign fibrous strictures can be classified upon their endoscopic aspect in five main types: annular, mucous branches, semilunar, tortuous and tubular strictures. Multiple strictures are less commonly observed.
Treatment
Treatment options for esophageal strictures include conservative or surgical procedures. Conservative treatment includes mechanical stricture dilation (bougienage, balloon catheter dilation) and prosthesis placement. A technique using endoscopic electrocautery incisions of the stricture prior to dilation has been proposed and is successfully performed by the author. Surgery is not commonly performed on the esophagus because it is technically demanding and often complicated; it includes resection and anastomosis, esophagoplasty or reconstructive procedures (patch grafting), and is indicated when conservative treatment fails or in case of neoplastic or tubular strictures.
Complication
The most severe complication of stricture dilation and electrocautery is esophageal perforation, while complications of prosthesis placement are prosthesis obstruction and dislocation in the gastric cavity and mechanical lesions with fistula formation of the esophageal wall. Gastric over distension can be a common complication of endoscopy in animals with strictures, since air inflated with the endoscope cannot be aspirated if the stricture precludes passage of the endoscope in the stomach.
Indications
Esophagoscopy is a very useful tool in the diagnosis and treatment of esophageal diseases. It is a highly reliable diagnostic method for evaluating esophageal disorders that affect the mucosa or alter the lumen of the organ. Esophagoscopy allows the procurement of cytology and histology samples. The most common mucosal and luminal abnormalities diagnosed by esophagoscopy are foreign bodies, esophagitis and strictures. Esophageal ulcers, fistula and neoplasia are less frequently encountered in dogs and cats. Megaesophagus, diverticula, vascular ring anomalies and hiatal disorders are best investigated by contrast radiography, however endoscopy can give a more accurate and accessory information in these conditions. Indications for esophagoscopy include clinical signs referable to esophageal disease, including regurgitation, dysphagia, odynophagia and unexplained salivation.
Esophagoscopy has also a useful therapeutic role. The main therapeutic indications of esophagoscopy are the retrieval of foreign bodies and the dilation of esophageal strictures under direct visualization. A range of grasping forceps assists the endoscopist in grasping and carefully retrieving the foreign body. An accurate evaluation of the esophagus after removal is important to assess the mucosal damage and rule out perforation. Conservative treatment of benign esophageal strictures is currently the most reliable approach to this condition in animals and humans. Mechanical dilation of strictures is achieved using balloon catheter dilation or bougienage. A technique using endoscopic electrocautery incisions of the stricture prior to balloon dilation has been proposed by the author.
Patient preparation
A 12 hours withdrawal of food is required for patients undergoing esophagoscopy. Contrastographic studies should be avoid prior to esophagoscopy because barium can interfere with the examination. If necessary, water-soluble, nonionic, iodinated agents should be preferred, although for contrast study of the esophagus a barium sulphate esophageal cream would be more indicated. Saline lavage or suction may be used to remove the residual contrast medium. General anesthesia is required; the patient should be placed in left lateral recumbency, with an endotracheal tube and a mouth gag in place. Thoracic radiography should be accurately examined to rule out an esophageal perforation, since esophagoscopy should not be performed in such a case.
Esophagoscopy procedure and normal findings
Due to its simple tubular morphology, the esophagus is normally easily examined with an endoscope. With the patient's head and neck extended, the endoscope follows the dorsal aspect of the endotracheal tube in the mouth until the upper esophageal sphincter is reached dorsally to the larynx. The entrance to the cervical esophagus appears close but it offers a low resistance to a minimal pressure of the tip of the endoscope. If any resistance to this maneuver is felt, the endoscope should be pulled back and redirected in a central and dorsal position. Before advancing in the cervical esophagus, air is insufflated until the lumen is clearly visualized. The cervical esophagus has pliable, longitudinal mucosal folds that disappear with air insufflation. The normal esophageal mucosa of the dog is pale pink or grayish and the surface is smooth and glistening. Patches of pigmented mucosa may be observed in pigmented dog breeds such as Chow chow, Shar pei, etc. Some of the periesophageal structures leave an imprint on the flaccid wall of the esophagus. The outline of the trachea can be observed making a curved impression against the ventral wall of the cervical esophagus. In the middle third, when the esophagus approaches the base of the heart, the aortic arch is seen pulsating against the wall of the organ. By advancing the tip of the endoscope caudally the impression of the left principal bronchus is clearly seen. Sometimes, the imprint and pulsation of the left subclavian artery (proximal to, and on the same side of, the aortic arch), the left atrium (just distally to the left bronchus) and the azygos vein (in the distal third of the esophagus) may be seen. Slowly moving the endoscope along the esophagus, the gastroesophageal sphincter is easily reached. At the gastroesophageal junction the color of the mucosa sharply changes from pale pink to the red of gastric mucosa. The landmark between the two different epithelia (esophageal pavement and gastric cubic epithelium) is normally marked by an irregular margin sometime protruding for some millimeters into the esophageal lumen. Different aspects of this area may be observed in the normal patient and they should not be considered as pathologic. The lower esophageal sphincter may appear as a rosette folding of the mucosa, but different appearances may be normal as well. The normal lower esophageal sphincter is usually closed, although this feature is largely related to the anesthetic protocol used. Minimal or no resistance is usually encountered when advancing the endoscope trough the sphincter, but sometimes a left deviation of the abdominal tract of the esophagus requires a slight deflection of the tip of the endoscope to complete this maneuver. The examination of the lower esophageal sphincter is complete only after the visualization of its gastric side by endoscopic retroversion ("J" maneuver).
The esophagus of the cat differs from the esophagus of the dog for the presence of well evident submucosal vessels and for circular rings formed by circumferential mucosal folds giving a typical pattern to the distal tract.
Biopsy of the esophageal mucosa is usually difficult to obtain. The procurement of a mucosal specimen may be required when a mass lesion is present or when an esophagitis is suspected. While proliferative lesions can be easily biopsied with traditional biopsy forceps, the esophageal mucosa is tough and normally cannot be cut with these forceps. The tubular anatomy of the esophagus complicates the procedure. A forceps with a central spike fixing to the esophageal mucosa or a suction biopsy capsule is a valid alternative. A cytology sample obtained by brushing may be useful in case of esophageal neoplasia.
The main diagnostic indications for esophagoscopy and that will be discussed are: esophagitis, strictures, foreign bodies, neoplasia and hiatal disorders. Endoscopy may be useful also for esophageal diverticula and vascular ring anomalies.
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