Page 444 - Small Animal Internal Medicine, 6th Edition

416 PART III Digestive System Disorders

IMAGING OF THE ORAL CAVITY, obvious megaesophagus on plain radiographs is usually suf-
PHARYNX, AND ESOPHAGUS ficient, but rare dogs with apparent megaesophagus on plain
VetBooks.ir INDICATIONS radiographs demonstrate normal function when barium is
administered. Ultrasonography, CT, and MRI are seldom
Animals with dysphagia, oral pain, halitosis of unknown
there is a thoracic mass.
cause, or a swelling or mass should generally undergo helpful for dogs and cats with esophageal disease, unless
imaging. If dysphagia of neuromuscular origin is suspected,
dynamic contrast studies (i.e., fluoroscopy) are recom- Techniques
mended. Ultrasonography can be useful for evaluating infil- Liquid barium is the best contrast agent for esophageal
trates or masses, but magnetic resonance imaging (MRI) studies. It provides excellent detail and is not problematic
offers even more detail. if aspirated unless there is preexisting pneumonia. The cli-
nician must not administer drugs that affect esophageal
Techniques motility (e.g., xylazine, ketamine, anesthesia). The animal
Anesthesia is necessary so that animals can be properly posi- should take several swallows of dilute barium from a syringe,
tioned for cranial radiographs. Lateral, dorsoventral (DV), shortly after which right lateral and VD radiographs are
and oblique radiographs are used to detect foreign objects or obtained. Barium paste does not offer any substantive
fractures. Open-mouth ventrodorsal (VD) views and end-on advantages over liquid barium. Hypertonic iodine contrast
views of the nose may also be helpful. Computed tomogra- agents do not achieve as good a contrast as barium and
phy (CT) is superior to radiographs (and easier) for finding cause severe problems if aspirated; isotonic water-soluble
fractures, and a helical CT can perform the examination so iodine contrast agents are better but still provide medio-
quickly that deep sedation may be all that is needed. MRI is cre contrast. If radiographic studies performed with liquid
superior to CT for detecting soft tissue lesions. Dynamic contrast agents do not detect an abnormality in an animal
studies (i.e., fluoroscopy, cinefluoroscopy) are necessary to in which esophageal disease is strongly suspected, the study
evaluate for dysphagia of neuromuscular origin. Dynamic should be repeated using a mixture of barium and food
studies are performed by feeding conscious animals various (both canned food and dry kibble). Such studies may detect
forms of barium (i.e., liquid, paste, and mixed with food). partial strictures or muscular weakness not found with
Performing dynamic studies in sternal recumbency is pre- previous studies.
ferred because lateral recumbency might increase transit If barium is retained in the esophagus but little or none
time and change the type of peristaltic waves. enters the stomach, the animal should be held in a vertical
position so that gravity facilitates migration of barium into
Findings the stomach. If barium readily enters the stomach, this indi-
Foreign objects, fractures, bone lysis, soft tissue masses or cates that there is no lower esophageal sphincter obstruction.
densities, and emphysema are the most common findings. If a hiatal hernia is suspected but not seen, a lateral radio-
Bone surrounding the tooth roots should be examined for graph of the caudal thorax may be taken while the abdomen
lysis and the temporomandibular joints for arthritis. It is is manually compressed. This is done in an attempt to force
important to consider the bilateral symmetry of the skull; the contrast-filled stomach to herniate into the thorax, allow-
one side should be compared with the other when evaluating ing diagnosis.
the VD projection. When performing contrast-enhanced or If esophageal disease seems likely but is not found by
dynamic studies, the clinician should watch for aspiration static radiographs, fluoroscopic studies are indicated next.
of barium, the strength with which the bolus is propelled If possible, the clinician should perform fluoroscopy as the
into the esophagus, and synchronization of the opening of animal swallows the barium to assess esophageal motility and
the cricopharyngeal muscle with the pharyngeal phase of look for partial esophageal obstruction, segmental esopha-
swallowing. geal weakness, gastroesophageal reflux, and esophageal-
pharyngeal reflux (i.e., cricopharyngeal incompetence).
INDICATIONS FOR IMAGING Having the patient in sternal recumbency is preferred for
OF THE ESOPHAGUS dynamic studies. It may be necessary to observe the esopha-
Indications for evaluating the esophagus include any type gus for several minutes (or longer) before some abnormali-
of neuromuscular dysphagia, regurgitation, pain when ties (e.g., gastroesophageal or esophageal-pharyngeal reflux)
swallowing, unexplained recurrent pneumonia or cough, occur. In animals with marginal esophageal disease, fluoros-
radiographic thoracic “masses” of undetermined origin, copy may be necessary to document that primary or sec-
and before surgical lateralization of arytenoids for laryn- ondary esophageal waves are present but are either weak or
geal paralysis. A barium contrast esophagram is often nec- not readily stimulated. If fluoroscopy is unavailable, multiple
essary to define esophageal pathology unless plain films radiographs (usually lateral projections) taken in rapid suc-
reveal obvious megaesophagus, a foreign object, evidence cession beginning very shortly (i.e., 5-10 seconds) after swal-
of esophageal perforation (e.g., a pleural effusion, pneu- lowing are sometimes adequate.
mothorax, pneumomediastinum), or an obvious hiatal If an esophageal perforation is suspected (e.g., sep-
hernia. Be sure to include the cervical esophagus. Finding tic pleuritis or mediastinitis, pneumomediastinum, or