Pharyngeal Dysphagia and Cricopharyngeal Achalasia

A number of abnormalities may affect the oropharynx, and they are difficult to distinguish from one another. Both the oropharynx and nasopharynx should be examined. Plain radiographs are seldom diagnostic in cases of dysphagia. These are functional disorders and require fluoroscopy to make a definitive diagnosis.

In pharyngeal dysphagia resulting from structural or neurologic disorders, inefficiency of pharyngeal contractions results in the retention of food material within the pharynx. Affected animals make repeated efforts to swallow food. Coughing may occur. Food material may come down the nose. Aspiration pneumonia is common. With fluoroscopy, a barium examination will show retention of barium in the pharynx despite repeated efforts to swallow it. Barium may enter the trachea, and air is often seen within the esophagus.

Cricopharyngeal achalasia results from failure of the cricopharyngeus muscle to relax during swallowing or from lack of coordination of the mechanisms involved in swallowing. The clinical signs are similar to those seen in pharyngeal dysphagia. A barium study shows retention of barium in the pharynx and cervical esophagus. On fluoroscopy, pharyngeal contractions are seen to force the barium against the caudal wall of the pharynx, with only a small amount of barium entering the esophagus, where it tends to remain. Barium may come down the nose or enter the larynx or trachea. Failure of the cricopharyngeus muscle to relax can be treated surgically. However, cricopharyngeal myotomy is contraindicated in other disorders of this region. Hence, accurate diagnosis is important.

Pharyngeal dysphagia and cricopharyngeal achalasia should be considered in the differential diagnosis in young animals that have difficulty swallowing.

Laryngeal Paralysis

As a result of paralysis of the laryngeal muscles, the laryngeal airway does not open adequately during respiration. Clinically, there is a moist cough and, in more severe cases, a loud inspiratory noise.

The condition may be the result of a variety of causes. It may be hereditary, particularly in the larger breeds such as the Dalmatian and the English Bulldog. It is most common in the Labrador and Golden Retriever. It is rare in cats. Other causes include trauma, inflammation, and neoplasia, or it may be the result of a systemic condition such as hypoparathyroidism. It may be idiopathic.

Radiologic signs may be absent. Obstruction of the upper airway may result in hyperinflation of the lungs. The tracheal lumen may vary in width. There may be aspiration pneumonia. Pulmonary edema may form.

Brachycephalic Airway Syndrome

This is seen in brachycephalic dogs as a combination of elongated soft palate and various laryngeal abnormalities such as paralysis. The pharynx is small, and the hyoid apparatus is directed vertically (Figure 3-1, E and F).

Laryngeal Hypoplasia

This condition is common in brachycephalic breeds and in the Skye Terrier. The laryngeal cartilages are soft and underdeveloped. This results in partial obstruction of the upper airway. The degree of respiratory distress caused depends on the severity of the abnormality. Clinical and radiologic findings are consistent with obstruction of the upper airway.

Displacement

The trachea may be displaced by cranial lung lobes, pleural, cervical, or mediastinal masses or by an enlarged heart. Adjacent masses tend to displace rather than compress it. Compression may occur at the thoracic inlet or over the base of the heart. The trachea may be compressed between a mass and the ribs, the spine, the aorta, or the heart, which are all relatively rigid structures.

A distended esophagus may displace the trachea ventrally. An enlarged heart displaces the trachea dorsally. Cranial mediastinal masses usually displace it dorsally and laterally, and they may displace the terminal trachea caudally. Intrathoracic masses may displace the tracheal bifurcation cranially. Enlarged tracheobronchial lymph nodes may depress, elevate, or compress the trachea and separate the mainstem bronchi.

Before making a diagnosis of tracheal displacement, one must be sure that the animal has been positioned correctly. Undue extension may result in the trachea appearing compressed at the thoracic inlet (Figure 3-3, A). Extreme flexion of the neck during radiography may result in a ventral displacement of the trachea in the cranial thorax (Figure 3-3, B and C). Dorsal displacement may be seen with lateral or ventral flexion of the neck. This results in artifactual displacement of the trachea in the cranial mediastinum, simulating a mass (Figure 3-3, C and D). Rotation of the thorax on the lateral view will cause an apparent elevation. Some deviation of the trachea to the right is often seen in normal dogs in the cranial thorax. It may be more pronounced in brachycephalic breeds (see Figure 3-29, G). A ventrodorsal or dorsoventral view is required to demonstrate deviation in the lateral plane (Figure 3-3, E).

Figure 3-3 A, Pseudonarrowing of the trachea at the thoracic inlet from hyperextension of the neck. B, A lateral view of the thorax with the neck flexed shows a slight bend in the trachea at the thoracic inlet from hyperflexion. C and D, Artifactual tracheal displacement in a dog. C, When the initial radiograph was obtained, the patient’s neck was partially flexed. There is dorsal displacement of the thoracic trachea, just cranial to the aortic arch. This displacement mimics dorsal tracheal deviation associated with a cranial mediastinal mass. D, A second radiograph was obtained with the dog’s head and neck in a neutral position. The trachea is now seen to be in a normal position, with no evidence of displacement. E, The trachea is displaced to the left by a mass in the neck. This was a thyroid mass. F and G, Tracheal collapse. A 7-year-old Yorkshire Terrier had been coughing in violent spasms for several months. Lateral studies of the trachea in expiration (F) and inspiration (G). The intrathoracic tracheal lumen is markedly narrowed at expiration, and the difference between the two phases of respiration is well demonstrated. H and I, A 9-year-old Boston Terrier was depressed, cyanotic, and tachypneic. H, A lateral radiograph shows severe narrowing of the intrathoracic trachea. There is widespread infi ltration of the lungs from hemorrhage. There is some air in the cervical esophagus. This was submucosal hemorrhage in the trachea caused by anticoagulant poisoning. I, Four days later there is almost complete resolution of the condition. (This is the same case as Figure 3-25, I and J.) J, This 1-year-old Pug had a history since birth of repetitive collapse after exercise. The tracheal lumen is grossly narrowed throughout its length. Diagnosis: tracheal hypoplasia.

Collapse

Tracheal collapse affects the smaller breeds of dogs in middle to old age. It may be acquired or congenital. The congenital form manifests itself in later life. The clinical signs comprise varying degrees of respiratory distress and a paroxysmal, chronic, dry “goose honk” cough. Because the usual type of collapse is in the dorsoventral plane, lateral radiographs are the most informative. Both inspiratory and expiratory radiographs of the full length of the trachea should be made with the forelimbs at right angles to the spine. A skyline or tangential view of the thoracic inlet with the dog in sternal recumbency and the head and neck extended dorsally is occasionally useful (see Figure 3-2, B). Extreme care should be taken because such positioning may exacerbate the clinical signs.

Hypoplasia

Congenital hypoplasia (congenital stenosis) is seen in some brachycephalic breeds such as the English Bulldog and the Bullmastiff. It is occasionally seen in other breeds such as the German Shepherd, the Labrador Retriever, and the Basset Hound. It is rare in cats. The tracheal lumen size is grossly narrowed, usually throughout its length. The diameter may be less than half that of the larynx or less than the width of the proximal third of the third rib. With hypoplasia, there is no variation in diameter on inspiratory and expiratory radiographs or during fluoroscopy (Figure 3-3, J). Aspiration pneumonia may be a complicating factor. The trachea may be narrowed as a result of intramural hemorrhage (Figure 3-3, H and I).

Neoplasia

Neoplasia of the trachea is rarely seen in dogs and cats. Osteosarcoma, chondroma, adenocarcinoma, and squamous cell carcinoma have been reported. A neoplastic mass projecting into the tracheal lumen can be seen because of the air that surrounds it. The use of contrast medium (bronchography) is sometimes helpful in differentiating between intraluminal and extraluminal masses. However, endoscopy has superseded traditional contrast studies.

Calcification

Calcification of the tracheal rings is sometimes seen in older dogs, particularly in the chondrodystrophoid breeds. It does not appear to have any significance (Figure 3-4, A).

Figure 3-4 A, Calcification of the trachea. B, This Spaniel was in a dog fight 14 days previously. The tracheal lumen is markedly narrowed by a soft tissue mass, and the contour of the tracheal rings is disrupted. Diagnosis: tracheal stenosis. C, This 11-month-old Dandie Dinmont Terrier presented with a history of severe exercise intolerance and a marked wheeze. Discrete soft tissue opacities are evident within the intrathoracic tracheal lumen (arrows). Diagnosis: Oslerus osleri infestation.

Rupture

If the trachea is punctured, air escapes into the peritracheal tissues, and subcutaneous emphysema can be recognized on radiographs as air opacities beneath the skin. Air may also be seen dissecting along fascial planes in the soft tissues. Pneumomediastinum may result if the rupture is within the thorax, or air may track into the mediastinum from an extrathoracic rupture. Damage to the tracheal rings may result in narrowing of the lumen and ultimately stenosis.

Stenosis

Stenosis, or narrowing of the trachea, may be seen on lateral studies. It may occur in dogs or cats after laceration, direct blunt trauma, or bite wounds (Figure 3-4, B).

Oslerus osleri

Irregularities in the tracheal lumen and soft tissue opacities projecting into it, with increased peribronchial radiopacities in the perihilar area, have been described in association with Oslerus osleri (Filaroides osleri) infestation. Diagnosis is more certainly achieved by demonstrating larvae in fecal samples or tracheal washings or by endoscopy (Figure 3-4, C).

Avulsion

This is a disruption in continuity of the tracheal rings within the thorax. It is seen in cats after trauma. The clinical signs include dyspnea, exercise intolerance, and cyanosis on exercise. At the time of injury there may be no respiratory signs. Radiologically there is loss of continuity of the tracheal lumen and an irregular outline to the tracheal margins. Often there is an air-filled bulge dorsally at the site of disruption. Avulsion of the left or right mainstem bronchus has also been encountered. Surgical repair has been described.

Obstruction

Foreign body obstruction of the trachea is not common. The main clinical finding is sudden bouts of severe coughing. The air-filled trachea provides a good contrast background against which a foreign body can usually be seen (see Figures 3-2, C and D, and 3-5, A and B). If the foreign body is radiolucent, endoscopy may be more informative. Obstruction of the trachea may result in hyperinflated lung fields due to a ball-valve effect, resulting in difficulty in expelling air. If a foreign body passes into a bronchus, the resulting atelectasis may obscure it. No air bronchograms will be seen in the atelectatic lobe because the presence of fluid obliterates contrast between the bronchi and the lung. Flexion of the neck with an endotracheal tube in place may cause kinking of the tube and obstruction of the airway (Figure 3-5, C).

Figure 3-5 A, This 3-month-old Boxer had a chronic cough. A discrete radiopaque foreign body lies in the distal trachea. Some air is present in the esophagus. A piece of gravel was successfully removed during endoscopy. B, A radiopaque foreign body in the trachea. C, The neck is flexed, causing obstruction of the endotracheal tube.

(B, Courtesy Dr. Colin Healy.)

Tracheitis

There are usually no radiographic signs of tracheitis. Intratracheal exudation and mucosal swelling may cause the tracheal lumen to appear less sharp than usual.

Lateral View

The animal is placed in lateral recumbency. The forelimbs are drawn cranially and positioned parallel to one another. This position prevents superimposition of the triceps muscles on the apical portions of the cranial lung lobes. The sternum should be supported and should be on the same level and parallel to the thoracic vertebrae so that there is no rotation of the thorax relative to the incident x-ray beam. The neck is extended, or at least not flexed. The beam is centered at the fifth intercostal space, usually at the caudal edge of the scapula. There is little difference between radiographs made in left lateral recumbency and those made in right lateral recumbency. Right lateral recumbency may be preferred because in this position the phrenicopericardial ligament restricts movement of the cardiac apex toward the dependent side.

If pathology is suspected in one lung, that lung should be uppermost because the dependent lung does not inflate fully, and contrast in it is therefore diminished. For this reason, two opposing lateral studies are needed to fully evaluate both lungs. Standing lateral views are occasionally useful if pleural fluid or air is suspected. For this view, the cassette is positioned along the thoracic wall with the animal in the standing position. A horizontal beam is used, centered on the fifth intercostal space. A lateral view, using a horizontal beam and with the animal in sternal recumbency, is an alternative. Dorsal recumbency using a horizontal beam is occasionally used to examine the ventral thoracic region, but this position requires care in animals with compromised respiration.

Dorsoventral and Ventrodorsal Views

The cardiac outline is less distorted on the dorsoventral view, that is, with the animal in sternal recumbency. If the cardiac shadow is the main item of interest, the dorsoventral view is preferable. The vessels to the caudal lung lobes are better seen on this view. To obtain a dorsoventral view, the animal is placed in sternal (ventral) recumbency with the elbows abducted and the forelimbs drawn slightly forward. The hindlimbs are flexed, with the hocks resting on the table. The head is positioned between the forelimbs on the midline. The thorax should not be rotated. The thoracic vertebrae should overlie the sternum. The beam is centered over the caudal edge of the scapula.

To obtain a ventrodorsal view, the animal is placed in dorsal recumbency with the forelimbs drawn forward and the beam centered over the caudal edge of the scapula. The sternum should overlie the thoracic vertebrae. When the animal is in dorsal recumbency, for a ventrodorsal view, gravity tends to move the heart away from the sternum. However, positioning is often easier with the animal in dorsal recumbency, and better inspiratory films can be obtained in this position. It is therefore the preferred study for lung evaluation. Placing the animal on its back may increase distress in cases with dyspnea. In such cases, a dorsoventral view should be used.

Oblique View

Oblique views are sometimes helpful in demonstrating areas of lung tissue that are obscured by the cardiac silhouette on more conventional views. They may also be useful in studying the trachea and esophagus. Lesion-oriented oblique views may be required to demonstrate masses on the thoracic wall or on the ribs.