Relative Value of Radiography, Contrast Esophagraphy, Fluoroscopy, and Alternative Imaging Procedures

Survey radiographs of the thorax and cervical region, including the base of the tongue, are indicated in dogs and cats with clinical signs of esophageal disease. Survey radiographs and static barium esophagraphy provide structural information about the size and content of the esophagus and allow assessment of aspiration pneumonia and signs of esophageal perforation. Static contrast esophagraphy is helpful for characterizing the following conditions: esophageal mass, nonradiopaque foreign body, esophageal stricture, vascular ring anomaly, esophageal perforation, esophagitis, esophageal diverticulum, tracheo- or bronchoesophageal fistula, dysphagia, and hiatal hernia.² Static contrast esophagraphy is not adequate for assessing dysphagia, where dynamic contrast studies performed with fluoroscopy are required. Dynamic studies are typically performed at specialty centers.

Other than positive contrast radiography, other modalities are used only rarely to assess the esophagus. Scintigraphy can be used to quantify esophageal motility and transit time and diagnose gastroesophageal reflux.³ Computed tomography (CT) is helpful for further characterization of esophageal masses and their association with adjacent tissues and vessels for both diagnostic and presurgical purposes. Radiographic or CT angiography is required for the characterization of vascular ring anomalies and esophageal varices. Conventional transcutaneous ultrasonography is limited to evaluation of the cervical esophagus and, to some extent, the caudal esophageal sphincter and gastroesophageal junction. Endoscopic ultrasonography can be used to examine the thoracic portion of the esophagus.⁴ Indications include mural infiltration, fistula, diverticula, and periesophageal masses. Magnetic resonance imaging is not used for esophageal examination in animals but is used frequently to assess esophageal tumors in human beings.

Anatomy and Physiologic Considerations

The esophagus begins cranially at the cricopharyngeal sphincter, also called the cranial esophageal sphincter, and continues to the esophageal hiatus at the diaphragm. The cricopharyngeal sphincter is formed by the cricopharyngeus and thyropharyngeus muscles. In the cranial aspect of the thorax, the esophagus is related closely to the longus colli and longus capitis muscles dorsally and to the trachea ventrally and to the right.⁵ In the neck, the cervical esophagus is located slightly to the left of the trachea, gradually becoming completely left-sided at the thoracic inlet (Fig. 27-2, A).⁵ The left common carotid artery, vagosympathetic trunk, internal jugular vein, and tracheal duct course through the angle between the esophagus and the longus capitis muscle. The right common carotid artery, vagosympathetic trunk, internal jugular vein, and tracheal duct are lateral to the trachea on the right side. The thoracic portion of the esophagus is in close proximity to the trachea. The esophagus is to the left of the trachea at the thoracic inlet (Fig. 27-2, B), but it gradually courses dorsally over the point of bifurcation of the trachea at the level of the fifth and sixth thoracic vertebrae (Fig. 27-2, C). At its dorsal location, it lies to the right of the aortic arch and is ventral to the longus colli muscles. Between the tracheal bifurcation and caudal esophageal sphincter, the esophagus lies in the median plane (Fig. 27-2, D). The vagal nerves run dorsocaudally across the sides of the esophagus and unite at the dorsal aspect of the esophagus a few centimeters cranial to the esophageal hiatus to form the vagal trunk, which passes through the hiatus with the esophagus.

There are numerous longitudinal folds of the esophageal mucosa (Fig. 27-3, A). The wall consists of four layers: fibrous, muscular, submucosa, and mucosa. The muscular layer is composed of striated muscle in dogs along its entire length, and the entire length of the mucosa is characterized by longitudinal folds. In cats, the caudal third of the muscular layer is composed of smooth muscle, which is arranged obliquely creating a striated pattern on contrast esophagrams (Fig. 27-3, B). The caudal esophageal sphincter is formed by the focal thickening of the esophageal smooth muscle of the muscularis, confluence of the gastric folds oriented transversely, and the muscular sling created by the right crus of the diaphragm and the deep oblique smooth muscle of the lesser curvature of the stomach.

Branches of the thyroid arteries supply the cervical portion of the esophagus, and the bronchoesophageal artery is the main source to the cranial two thirds of the thoracic portion. Esophageal branches of the aorta and/or intercostal arteries supply the remainder of the esophagus, and the terminal portion is supplied by the left gastric artery. The azygous vein and left gastric vein drain the thoracic portion. Lymphatic drainage is through the medial retropharyngeal, deep cervical, cranial mediastinal, bronchial, portal, splenic, and gastric lymph nodes.

Innervation of the esophagus is complex and involves 25 paired spinal ganglia from C2-L5. Neurologic control of swallowing is coordinated by cranial nerves V (trigeminal), VII (facial), IX (glossopharyngeal), X (vagus), and XII (hypoglossal), and their nuclei in the brain stem that, in turn, are controlled by areas of the reticular formation referred to as the swallowing center.⁶

Normal Radiographic Appearance

The normal esophagus is usually empty and rarely evident on thoracic radiographs in cats and dogs because of its location within the mediastinum and silhouetting with adjacent muscles and mediastinal structures. On left lateral thoracic radiographs, the normal caudal thoracic esophagus sometimes contains a small amount of fluid and can be visualized as a faint tubular soft tissue opacity between the descending aorta and caudal vena cava (Fig. 27-4, A); this appearance is rare in right lateral radiographs. Gas can accumulate focally in the esophagus in animals that are excited, sedated, and dyspneic or under general anesthesia; this gas accumulation is usually minimal, and the most common location for this to occur is just cranial to the tracheal bifurcation (Fig. 27-4, B). Focal esophageal gas collections are dynamic and may appear differently or be absent in other radiographs acquired during the same study. General anesthesia or aerophagia may even lead to severe dilation of the esophagus, which can appear identical to pathologic megaesophagus (Fig. 27-4, C). Anesthesia-related megaesophagus will resolve spontaneously when the patient has recovered from anesthesia.

Survey Radiographic Abnormalities

Box 27-1 contains a list of radiographic signs that can be seen with esophageal disease. Gas in the esophageal lumen warrants further investigation in patients where it is thought to be pathologic and not a normal variant as described previously (see Fig. 27-4). It is important to examine the entire esophagus radiographically, meaning that radiographs of the cervical esophagus and pharynx are warranted in addition to thoracic radiographs (Fig. 27-5).

There may be a tendency to confuse esophageal gas with pneumomediastinum, although there are some basic differences in the appearance of these conditions. With pneumomediastinum, there will be increased conspicuity of the adventitial surface of the esophagus and great vessels, as described in Chapter 30. With megaesophagus, the gas collection will be more contiguous, and a tracheal stripe sign will be present. The tracheal stripe sign is a soft tissue opaque band that is formed by the summation of the ventral aspect of the esophageal wall with the dorsal aspect of the tracheal wall, each outlined by gas in their respective lumen (Fig. 27-6; see Fig. 27-4). If the gas-filled esophagus is large enough, the ventral border of the longus colli muscle and the dorsal indentation created by the overlying azygos vein will be visible (see Fig. 27-6).

When esophageal air is detected in animals with clinical signs of esophageal disease, an esophagram is indicated to rule out morphologic abnormalities such as a stricture or nonradiopaque foreign body. Normal variations such as kinks and bends in the cranial portion of the thoracic esophagus, sometimes referred to as redundant esophagus, can be identified in young dogs or short-necked brachycephalic breeds (Fig. 27-7). Contrast medium can accumulate temporarily in a redundant section and can appear as an outpouching as with an esophageal diverticula. Dynamic esophagraphy is needed to assess the significance of esophageal redundancy, as in some dogs the motility may be altered significantly in this region.

The absence of abnormal esophageal survey radiographic findings does not eliminate the possibility of esophageal disease. In animals with appropriate clinical signs but clinical signs of esophageal disease, contrast studies of the esophagus should be considered.

Contrast Esophagraphy Techniques

Survey radiographs of the thorax and cervical region must always be performed immediately before a contrast esophagram. Static contrast studies provide structural information, whereas fluoroscopy is required to assess swallowing disorders and esophageal motility. Table 27-1 lists the types of contrast media that can be used for an esophagram, along with their advantages and disadvantages. Barium aspiration is a potential complication of performing esophageal contrast studies. Barium paste is contraindicated in animals at increased risk for aspiration because aspirated paste could cause airway obstruction. Aspiration of a small amount of liquid barium is usually insignificant. Pneumonia and lung granuloma formation are rare complications of barium aspiration. Aspirated barium is cleared from the airways by ciliary action, as well as coughing (Fig. 27-8). If barium enters the alveolar space, it may remain there permanently. Lymphatic uptake of aspirated barium will also be evident as amorphous mottled opacities in the region of the mediastinal and tracheobronchial lymph nodes, which may also be a permanent finding (Fig. 27-9).

Box 27-2 contains a list of contrast study techniques used for examination of the esophagus.⁷ The esophagram should be performed without sedation because most sedatives have an effect on esophageal motility and swallowing. Table 27-2 contains a description of the phases of swallowing and normal radiographic appearance of contrast studies. In general, there should be no retention of barium in the oral or pharyngeal cavity in static radiographs performed during swallowing. Some coating of the mucosa is normal. No contrast medium should be present in the pharynx, larynx, or trachea after swallowing.

Dysphagia

Dysphagia can result from morphologic or functional etiologies. Morphologic causes include trauma, foreign body, an oral or pharyngeal mass, and regional lymphadenopathy. Lateral and ventrodorsal (VD) survey radiographs of the pharyngeal and cervical region and thorax are indicated to screen for radiopaque foreign bodies such as bones, needles, and fish hooks (Fig. 27-10). Soft tissue swelling and gas pockets can be seen with perforating pharyngeal trauma, abscesses, or a nonradiopaque foreign body such as a wooden stick. Ultrasonography is useful to determine the source of nonspecific pharyngeal swelling and nonradiopaque foreign bodies (Fig. 27-11).

Evaluation of functional disorders of swallowing requires contrast fluoroscopy (Table 27-3). Videofluoroscopic contrast studies allow subtle events of the oral, pharyngeal, and cricopharyngeal phases of swallowing to be recorded and observed dynamically.^a Frame rates of 30 to 60 per second are necessary to assess the rapid events of swallowing to make an accurate frame-by-frame analysis.⁶ The advantage of dynamic recordings is that subtle abnormalities associated with swallowing that would go unnoticed on static images can be detected. Cinescopy or digital fluoroscopy equipment will use slower acquisition rates of six images per second that also allow oral, pharyngeal (Fig. 27-12, A), cricopharyngeal (Fig. 27-12, B), and esophageal phases (Fig. 27-12, C) to be recorded, but subtle disease can go unnoticed as a result of the low frame rate.

Table • 27-3

Types of Dysphagia, Causes, and Fluoroscopy Findings

TYPE	CAUSES	FLUOROSCOPIC FEATURES
Oral	Neuromuscular disease Inflammation Oral foreign body Tongue abscess	Bolus not formed or delayed formation Bolus not propelled caudally to pharynx Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Related Related posts: Orthopedic Diseases of Young and Growing Dogs and Cats Principles of Radiographic Interpretation of the Thorax Principles of Radiographic Interpretation of the Axial Skeleton The Equine Thorax Stay updated, free articles. Join our Telegram channel Join Tags: Textbook of Veterinary Diagnostic Radiology May 27, 2016 | Posted by admin in ANIMAL RADIOLOGY | Comments Off on The Canine and Feline Esophagus Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access