Symposium on Gastroenterology
Contrast Radiography of the
Digestive Tract
Indications, Techniques, and Complications
William R. Brawner, Jr., D.V.M., Ph.D.,*
and jan E. Bartels, D.V.M., M.S.t
Radiography is an important diagnostic aid in the evaluation of small
animals with signs of esophageal or gastrointestinal disease. Thoracic or
abdominal radiography may provide useful information about digestive
disorders, but that information is often limited by the inherently poor
visibility of the esophagus, stomach, and intestines on survey (plain film)
radiographs. Radiographic visualization of anatomic structures depends on
the variable absorption of X-rays by organs and tissues of varying thickness
and chemical composition. Based on tissue composition, there are four
distinct radiographic densities of biologic materials: gas, fat, fluid, and
bone, in increasing order of radiodensity. Differences in density among
body structures provide natural subject contrast and allow radiographic
visualization of these structures. Perception of borders or margins is the
key feature in recognition of anatomic structures on radiographs. Margins
are perceived where there is a distinct density gradient. When two
structures of the same density are in contact, the confluent borders cannot
be distinguished.
Radiographs of extremities yield excellent skeletal contrast because
bone is much more radiodense than the surrounding soft tissue. The thorax
also has excellent natural subject contrast created by the presence of air
(gas) in the lungs. The heart, pulmonary vasculature, and interstitium of
the lungs are clearly contrasted against the alveolar spaces. Conversely,
radiographs of the abdomen have poor natural subject contra£t because all
intra-abdominal organs are composed of fluid-density tissues. The outlines
of these organs are visible only because fat separates the serosal borders.
Abundant intra-abdominal fat improves contrast and visualization of abdom*Diplomate, American College of Veterinary Radiology; Assistant Professor, Department of
Radiology, Auburn University School of Veterinary Medicine, Auburn, Alabama
tDiplomate, American College of Veterinary Radiology; Professor and Head, Department of
Radiology, Auburn University School of Veterinary Medicine, Al'lburn, Alabama
Veterinary Clinics of North America: Small Animal Practice-Yo!. 13, No. 3, August 1983
599
600
WILLIAM
R.
BRAWNER. jR. AND jAN
E.
BARTELS
Figure l. Survey (plain film) abdominal
radiographs of an emaciated dog (A), a
healthy, well-conditioned dog (B), and a fat
cat (C). Visualization of abdominal organs on
survey radiographs is possible only when fat
separates the serosal borders of the organs.
Increased fat accumulation separates organs,
provides more contrast, and thus enhances
visualization. Cats typically have more intraabdominal fat than do dogs.
inal viscera. Absence of intra-abdominal fat in emaciated or very young
animals, or fluid accumulation in the peritoneal cavity, obscures serosal
margins and causes poor radiographic visualization (Fig. 1). Gas within the
lumen of the gastrointestinal tract may aid in identification of segments of
the tract, but the presence of naturally occurring gas is inconsistent.
Because of poor natural subject contrast in the abdomen, it is often
useful to enhance radiographic visualization of organs or organ systems by
administration of contrast materials at the time of examination. All contrast
procedures should, however, be immediately preceded by survey radiographs so that the "current status" is known before the radiographic
appearance is purposely altered. Contrast radiography of the gastrointestinal
system is often essential to the thorough radiographic evaluation of a dog
or cat with esophageal or gastrointestinal disease.
INDICATIONS
Gastrointestinal contrast radiography is indicated when diagnosis or an
appropriate treatment cannot be determined from survey radiographs and
other clinical information. For the purpose of radiographic contrast administration, the digestive tract can be divided into three segments: esophagus,
stomach and small bowel, and large bowel. The contrast procedures most
commonly employed to examine these three segments are the es~phago­
gram, the upper gastrointestinal series, and the barium enema\ It is
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
601
important to decide which segment of the patient's gastrointestinal tract is
affected so that the most appropriate contrast proce.dure can be chosen.
The affected segment usually can be Jetermined by careful evaluation of
the history, clinical signs, and physical examination. Specific radiographic
contrast procedures are therefore indicated by presenting signs of disease
(Table 1).
Many instances of gastrointestinal disease in pet animals are transient
illness such as dietary indiscretion and other self-limiting conditions.
Animals that are not severely ill and that have recent onset of clinical signs
may best be treated symptomatically after the initial clinical examination.
Abdominal radiography and especially gastrointestinal contrast procedures
are generally reserved for chronic or persistent disorders. Radiography is
indicated in the patient with recent onset of signs when those signs suggest
serious or life-threatening disease. In the critical patient, it is often
necessary to choose between contrast radiographic procedures and exploratory surgery. If survey radiographs of the abdomen show evidence of
obstruction or perforation of the gastrointestinal tract or if there are other
signs of imminent life-threatening disease, then immediate surgical exploration is indicated. If surgery is not justified, contrast radiographic procedures may be considered after medical stabilization of the patient.
Table 1.
CONTRAST PROCEDURE
Indications for Gastrointestinal Contrast Radiography*
INDICATIONS
Esophagogram
Dysphagia
Regurgitation
Presence of mediastinal mass on survey radiographs
Unexplained presence of intraluminal esophageal gas on survey
radiographs
"Barium Burger"
Persistent regurgitation with normal survey radiographs and
esophagram
Upper GI Series
(Barium Series)
Vomiting
Small bowel diarrhea
Melena
Abdominal mass not completely defined by palpation or survey
radiographs
Suspected abdominal organ displacement
Pneumogastrogram
Demonstration of position of stomach
Suspected gastric foreign body
Double-Contrast
Gastrogram
Evaluatrion of gastric mucosa for ulceration, mass lesions
Suspected radiolucent gastric foreign body
Barium Enema
Large bowel diarrhea
Tenesmus
Fresh blood in feces or on bowel movement
Suspected intussusception
Pneumocolon
Demonstration of position of colon
Screen for large bowel obstruction
*When diagnosis or appropriate treatment cannot be deter~~;~ined by survey radiographs
and other clinical information.
602
WILLIAM
R. BRAWNER, JR. AND }AN E. BARTELS
SELECTION OF CONTRAST AGENT
Radiographic contrast procedures may be performed using positive
(radiodense) or negative (radiolucent) contrast media. Negative contrast
agents may be introduced into the gastrointestinal system by feeding
effervescent materials (carbon dioxide) or introducing air by stomach tube
or rectally. In veterinary radiology, the introduction of air by tube or
catheter is most commonly used because it is inexpensive and does not
require special materials or the voluntary cooperation of the patient. It
should be remembered that naturally occurring gas produced by the
digestive process affords a negative contrast and often facilitates visualization
of the gastrointestinal tract on survey radiographs.
Double-contrast radiographic procedures of the gastrointestinal tract
are performed by instilling a small amount of positive contrast material into
the stomach or colon and then distending the organ with a gas. Barium
sulfate suspensions are used in these procedures because of their ability to
adhere to mucosal surfaces. Double-contrast examinations allow excellent
visualization of the barium-coated mucosa, making them ideal for detection
of ulcers and other mucosal abnormalities.
The most common gastrointestinal contrast procedures used in veterinary practice employ positive contrast media. These radiopaque media are
administered orally, by stomach tube, or rectally to enhance radiographic
visualization of the esophagus, stomach, and intestines. Positive contrast
media can be divided into two major groups: barium sulfate preparations
and oral organic iodine solutions. Barium is available as USP barium powder
that is mixed with water to the desired consistency or as commercially
prepared pastes or suspensions of microfine barium particles. Organic
iodine media are available as liquid solutions (Gastrografin) or as powders
(oral Hypaque) that require mixing with water.
Commercially prepared barium suspensions are the best media for
routine use in gastrointestinal contrast radiography. Barium sulfate is
radiographically and physiologically superior to oral iodine solutions for use
in the digestive tract (Table 2). The commercially prepared barium suspensions are better than USP barium because they stay in suspension and
because they have coating agents that improve radiographic visualization of
mucosal detail. 15 Media prepared from USP barium and water often
flocculate or "clump" in the bowel as they come in contact with mucoproteins and as water is resorbed. The improved quality of the contrast study
is well worth the small additional cost of commercially prepared suspensions.
.
Both barium and organic iodine preparations have disadvantages that
must be considered under specific conditions. Barium preparations are
highly irritating when released into the mediastinum or peritoneal cavity
and cause a rapid and fulminating granulomatous inflammatory response.
In cases in which perforation, laceration, or rupture of the digestive tract
is suspected, oral organic iodine becomes the medium of choice for contrast
radiography. Organic iodine is innocuous in body. cavities; it is absorbed
and excreted through normal pathways, predominantly the urinary system.
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603
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
Table 2. Comparison of Barium Sulfate Suspensions and
Oral Organic Iodines as Gastrointestinal Contrast Agents
ADVANTAGES
DISADVANTAGES
LIQUID BARIUM SUSPENSIONS
(Commercial Preparations)
Very radiodense , provides excellent contrast
Excellent mucosal coating
Stays in suspension, not absorbed or diluted
Relatively inexpensive
Severe inflammation if released into body
cavity
Interferes at surgery
Not removed from alveoli if inhaled
ORAL ORGANIC IODINE SOLUTIONS
Innocuous in peritoneal cavity or
mediastinum
Rapid transit through stomach and
intestines
Not as radiodense as barium
Does not coat mucosa
Hypertonic solution draws body fluid into
gut lumen, dilutes the contrast further
Expensive
If no leakage of contrast is detected after administration of iodine but
perforation is still suspected, then administration of barium may be considered. Studies in human patients have shown that small perforations or
lacerations of the esophagus may go undetected on contrast radiographs
using organic iodine solution but can be demonstrated with barium preparations that coat the mucosa to define small defects. 1• 4 • 14
The extremely irritating nature of barium in the peritoneal cavity is
also a consideration when surgery must be performed immediately after
contrast radiography. When barium is present in the gut, special precaution
must be taken at surgery (enterotomy or resection) to avoid barium
contamination of the serosal and peritoneal surfaces. The thick, viscous
nature of barium suspension makes this a difficult and sometimes frustrating
task. In most cases, contrast radiography is used for chronic conditions that
do not require immediate surgery, but if a barium study does provide
indication for surgery, the operation can be accomplished safely.
Oral organic iodine contrast media are hypertonic solutions that cause
water to move from other fluid compartments into the gut lumen. This
fluid shift not only causes dilution of the iodine medium and loss of
radiographic contrast but also may compound fluid and electrolyte imbalances in animals with vomiting or diarrhea. Healthy adult animals tolerate
oral organic iodines well, but very young or marginally dehydrated animals
may become severely dehydrated or experience hypovolemic shock after
administration of these contrast media. These agents may also induce
vomiting in some animals. The use of oral organic iodine solutions is
contraindicated in dehydrated animals. Therefore, liquid barium suspension
should be used for contrast radiography in dogs and cats with chronic or
severe vomiting if a diagnosis cannot be made on survey radiographs.
Barium has been shown to be the safest contrast agent in cases of intestinal
obstruction. Controlled studies have shown that barium does not cause
impaction in obstructed dogs. 11
\.
604
WILLIAM
Table 3.
R. BRAWNER,
JR.
AND }AN
E. BARTELS
Contraindications for Administration of
Gastrointestinal Contrast Media
CONTRAST AGENT
CONTRAINDICATION
Barium Sulfate Preparations
Suspected perforation, laceration, or rupture of
esophagus, stomach, or intestine
Oral Organic Iodine Solutions
Dehydration, electrolyte imbalance, or shock
Barium or Iodine
Clinical examination and/or survey radiographic findings
adequate for diagnosis or indicative of need for
immediate surgery
In summary, the selection of gastrointestinal contrast medium is a
matter of clinical judgment. The superior properties of commercially
prepared barium sulfate suspensions make them the choice in most instances. It is important to remember that there are specific contraindications
to the use of barium and oral iodine media (Table 3).
TECHNIQUES AND COMPLICATIONS
The information gained from contrast radiography depends on the
quality of radiographs produced. Even an experienced radiologist cannot
make an accurate interpretation from inadequate films . The technical quality
of the examination is too frequently the limiting factor in contrast radiographic study of the digesitive tract. Careful attention must be paid not
only to radiographic technique (MAS, KVP, use of grid, and so forth) and
darkroom technique, but also to patient preparation, administration of
contrast medium, patient positioning, and timing of the sequence of
radiographs. Because many gastrointestinal contrast procedures require a
significant investment of time and materials, care must be taken to ensure
an examination of diagnostic quality. The opportunity to perform gastrointestinal contrast radiography is clearly a situation where one should follow
the adage, "If it's worth doing, it's worth doing right."
CONTRAST EXAMINATION OF THE ESOPHAGUS
Esophagogram
The esophagus is not visible on survey radiographs of normal dogs and
cats because it is contained within the mediastinum, where it is in contact
with other fluid-dense structures, and because there is no accumulation of
gas in the normal esophagus. Contrast examination is indicated in cases of
regurgitation or dysphagia when survey films show no esophageal abnormalities or inadequately define the extent or nature of an abnormality.
Because it allows ready differentiation of e,c;ophageal and extra-esophageal
masses, an esophagogram is also useful when a mediastinal mass is identified
on thoracic radiographs.
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
605
The esophagogram is one gastrointestinal contrast procedure that is
quick and easy to perform and does not require patient preparation. The
most important technical aspect of an esophagogram is the selection of the
proper contrast medium. When the contrast agent is swallowed, it moves
rapidly as a bolus to the stomach before radiographs are made. The medium
must coat the esophageal mucosa so that radiographs made 1 to 2 minutes
after the swallow will allow visualization of the esophageal lumen. The best
coating agent for routine studies is a thick barium paste. Barium pastes are
commercially available as "esophageal paste" or "esophageal cream" and
are usually provided in tubes that allow easy administration (Esophotrast).
A small amount (1 tsp to 1 tbsp) of barium paste is placed in the mouth
and patient is allowed to swallow. (If a fluoroscope is available, the barium
should be administered with the patient in l!J.teral recumbency so that the
progression of the bolus can be observed directly to evaluate the dynamics
of the swallowing reflex.) Lateral and ventrodorsal radiographs of the
cervical region and thorax are made 1 to 2 minutes after administration of
the barium . Slight oblique positioning of the ventrodorsal projection may
avoid direct superimposition of the thoracic spine and the esophagus.
Radiographs should be made promptly because swallowed saliva will soon
wash away the barium coating.
The normal canine esophagogram appears as linear streaks extending
the length of the esophagus as barium coats the crypts formed by longitudinal mucosal folds. (Fig. 2) In cats, esophageal contrast shows the linearstreaked pattern in the cranial two thirds of the esophagus but shows
transverse-oblique striations in the caudal esophagus (Fig. 3). There are
two normal variants that should be recognized as such to avoid misinterpretation: (1) an irregularity of the linear pattern at the thoracic inlet of
dogs caused by redundant mucosal folds, which should not be mistaken for
a pathologic dilatation (Fig. 4A); and (2) a barium bolus radiographed in
Figure 2. Normal canine esophagogram in lateral
(A) and ventrodorsal (B) projections. Linear !treaks of
barium paste extend the length of the esophagus.
606
WILLIAM R. BRAWNER.
JR.
AND }AN
E.
BARTELS
Figure 3. Normal feline esophagogram in lateral
(A) and ventrodorsal (B) projections. The transverseoblique striations in the caudal third of the esophagus
are a normal feature in cats but are not always seen as
prominently as in this example.
mid-swallow (Fig. 4B). Residual barium paste in the mouth may occasionally
be formed into a bolus and swallowed after the initial swallow. This second
bolus may, by chance, be swallowed just as a radiographic exposure is
made. The resultant "stop-action" picture of the barium bolus should not
be mistaken for dilatation. The differentiation can be made by repeat
radiography; a bolus will no longer be present but a true dilatation will
persist.
Figure 4. Common variants in the appearance
of normal canine esophagograms which may be mistaken for pathologic lesions. A, Redundant mucosal
folds at the thoracic inlet caused by ~xion of the
neck during radiography. B, A bolus of barium
radiographed in mid-swallow; the hoi s was not
present on repeat radiographs.
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
607
If the esophagus is dilated, contrast material will accumulate within
the lumen and a single swallow of barium may not fill the lumen adequately
for assessment of the extent of dilatation. In such cases, liquid barium
suspension may be administered orally to fill the dilated esophagus.
As noted earlier, oral iodine solution should be used in lieu of barium
if perforation of the esophagus is suspected. If the iodine study shows no
evidence of contrast leaking into the mediastinum, then a repeat study with
barium paste may be performed in an attempt to identify small mucosal
perforations or lacerations. 1• 4
The esophagogram is a safe procedure. The only complication of
consequence occurs when barium enters the mediastinal space through an
unsuspected perforation. Dysphagic dogs and cats may aspirate orally
administered media but because the paste is thick and volume is small, the
aspirated barium usually coats only the trachea and is removed by ciliary
action and coughing.
"Barium Burger"
"Barium burger" is a term used to describe an esophagogram using
barium mixed with solid food as the contrast agent. This procedure is
indicated when both survey radiography and a conventional esophagogram
fail to demonstrate an abnormality in a patient with dysphagia or regurgitation. A dysfunctional esophagus may allow passage of liquid but not solid
foods. In these cases an esophagogram using barium paste may show a
normal pattern, but the barium burger technique will demonstrate the
accumulation of food in the esophagus.
The procedure is simple. A small amount of barium paste or liquid
barium suspension is mixed with canned dog food; the food should maintain
its solid consistency. As animals with chronic swallowing disorders are
undernourished and often have a ravenous appetite, most animals will eat
the food voluntarily, but the mixture can be forced-fed if necessary. Lateral
and ventrodorsal radiographs of the cervical and thoracic regions are made
immediately after the patient consumes the barium-food mixture (Fig. 5).
Figure 5. Esophagograms made using barium cream (A) and liquid barium mixed with
canned dog food (B) in a dog that presented with persistent regurgitation. The barium-food
mixture ("barium burger") demonstrated dilatation not seen on a conventional esophagogram.
608
WILLIAM R. BRAWNER,
JR.
AND }AN
E.
BARTELS
CONTRAST EXAMINATION OF THE STOMACH AND SMALL
BOWEL
Upper GI Series
The upper GI series is also commonly known as the barium series and
is the standard contrast procedure for evaluation of the stomach and small
bowel. The stomach is filled with positive contrast material and sequential
radiographs are made to observe gastric emptying and the small bowel
follow-through. The upper GI series allows evaluation of the size, shape,
mucosal pattern, and position of the stomach and intestines and, by
employing sequential radiographs, allows assessment of progression of
material through the gastrointestinal tract. The upper GI series is indicated
when there are signs of gastric or small bowel disease (most often persistent
or recurrent vomiting or diarrhea) that cannot be diagnosed by survey
radiography and other clinical information. The procedure may also be
used to establish the position of the gastrointestinal tract in animals without
digestive disorders but with the possibility of abdominal masses or hernias.
A good quality upper GI series requires careful planning and preparation. Fortunately, the procedure is usually indicated for chronic conditions
and can be scheduled in advance. The patient should be fasted for 12 to 24
hours to allow emptying of the stomach and small intestine. Water should
be withheld for l to 2 hours before radiography to avoid the collection of a
large volume of fluid in the stomach at the time of administration of the
contrast material. Laxatives may be administered but are not essential if a
24-hour fast is enforced. Enemas should be administered prior to the
examination to ensure removal of all residual ingesta from the colon. This
is best accomplished by a series of large-volume warm water enemas.
Hypertonic enema solutions in disposable applicators usually do not provide
the thorough evacuation necessary. Cleansing of the large bowel should be
performed at least l to 2 hours before radiographic examination to allow
expulsion of the gas and fluid that are typically present just after administration of enemas . To ensure proper preparation it is often prudent to
hospitalize the patient the day before the upper GI series is scheduled.
The fast is best enforced under hospital supervision, and enemas can be
administered on the evening before and the morning of the contrast
examination.
Survey radiograp9s should always be made immediately before administration of the contrast medium, even if the abdomen has been recently
radiographed. These films allow verification of patient preparation and
provide a record of the "natural state" for comparison ~ith films made after
administration of the contrast agent. If ingesta are present in the gastrointestinal tract, the contrast procedure should be delayed for further preparation. Giving barium to an animal that has recently eaten rarely results in
a study of diagnostic quality and further delays the opportunity to begin an
adequate study. Occasionally the preliminary radiographs may yield diagnostic information that obviates the need for the contrast study.
Commercially prepared liquid barium suspension (Novopaque, Redipaque) is the best contrast medium for an upper GI series unless a
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
609
perforation of the stomach or intestine is suspected. Barium suspension can
be administered orally or by stomach tube. Most dogs and cats will accept
barium orally from a dose syringe. The patient's head is held in an elevated
position and barium is placed in the cheek pouch.
The proper dose rate for liquid barium suspension is 13 ml per kg (6
cc per lb or 1 oz per 5 lb). Administration of the full dose is essential to
the overall quality of the procedure. The initial dose of barium should
distend the stomach to allow visualization of its size and shape and to
stimulate gastric emptying. The goal of a good-quality barium series is to
have a broad, continuous ribbon of barium emptied into the duodenum
and jejunum.
If a gastric foreign body is suspected but not seen on survey radiographs, an initial dose of only 10 to 20 cc of barium should be administered
in an attempt to coat the foreign body and to avoid obscuring it in a dense
pool of barium. Dorsoventral, ventrodorsal, and left and right lateral
radiographs ar~ taken immediately. If no foreign body is seen then a full
dose of barium is given and the procedure is continued.
.
The timing of sequential radiographs is another important feature of
the upper GI series. Exposures should be made frequently during the first
hour to observe the stomach, gastric emptying, and the proximal small
bowel. After the first hour, the intervals may be increased but the study
should be followed until the barium column reaches the descending colon.
A typical film sequence is listed below, but clinical judgment should
determine the exact sequence of radiographs for each patient.
Typical Film Sequence for
Upper GI Series
Immediate
1 hour
15 minutes
2 hours
30 minutes
4 hours
(2 radiographic projections at each time)
If gastric emptying is obviously delayed, then the interval between
early films can be increased; if transit through the bowel is more rapid than
expected, the intervals can be shortened. An upper GI series should ideally
be started in the morning to allow time to follow the procedure to
conclusion.
Several factors may affect gastrointestinal motility, gastric emptying,
and small bowel transit time. Antiemetic and antidiarrheal drugs exert a
potent effect on gastrointestinal motility and, when possible, should be
discontinued 48 to 72 hours before an upper GI series is attempted.
Remember also that sympathetic stimulation (the "fight or flight" response)
dramatically decreases gastrointestinal motility. Gastric emptying and small
bowel transit are very slow in a frightened or enraged animal. For this
reason, it is especially important to be patient, gentle, and quiet when
administering barium or positioning a dog or cat for gastrointestinal contrast
radiography.
General anesthetics and many sedatives and narcotics decrease gastrointestinal motility. An upper GI series is best performed with no chemical
610
WILLIAM
R. BRAWNER,
JR.
AND }AN
E.
BARTELS
restraint, but mild sedation cannot be avoided in some fractious animals.
An unmanageable patient not only is difficult to position for radiography
but is almost certain to experience intense sympathetic stimulation. When
chemical restraint is required, we consider acepromazine maleate to be the
sedative of choice. Of the commonly available tranquilizers, it has been
shown to have the least effect on gastrointestinal motility. 14
Positioning of the patient is an important factor in performing an upper
GI series. The barium suspension used for contrast is a liquid and seeks
the lowest level in the stomach. Barium fills and distends the gastric fundus
when the patient is placed in left lateral recumbency. The pylorus is filled
in the right lateral recumbent radiograph. Similarly, the fundus is best
outlined in the dorsoventral projection (Fig. 6). If gastric disease is
suspected, radiographs should be made in dorsoventral, ventrodorsal, left
lateral and right lateral projections immediately after contrast administration
for optimal evaluation of the barium-filled stomach. Dorsoventral and right
lateral projections should be made at each interval during the upper GI
series. These projections favor visualization of the pyloric antrum and
proximal duodenum and allow best assessment of gastric emptying. A
common error in gastrointestinal contrast radiography is failure to take an
adequate number of films.
Figure 7 is a typical normal upper GI series in a dog. When the
stomach is well distended with barium, gastric emptying is stimulated. The
Text continued on page 614
Figure 6. Radiographic appearance of a barium-filled stomach with the patient positioned
for right lateral recumbent (A), left lateral recumbent (B), dorsoventral (C)~
· and ventrodorsal
(D) projections. Barium flows to the dependent portion of the stomach. Ro tine use of right
lateral and dorsoventral projections allows best assessment of the pyloric an rum and gastric
empyting. AIHour projections should be obtained for thorough evaluation of the stomach.
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
611
Figure 7. Upper GI series (barium series) in a healthy adult dog shows a typical film
sequence and progression of barium through the gastrointestinal tract. A and B, Survey
abdominal radiographs are always made immediately before contrast examination. C and D,
The stomach is distended with liquid barium immediately after administration.
Illustration continued on following page
612
WILLIAM
R.
BRAWNER.
JR.
AND jAN
E.
BARTELS
Figure 7 (Continued) . E and F, After 15 minutes the stomach and duodenum are well
visualized. G and H, After 30 minutes a continuous barium column fills the duodenum and
jejunum as the stomach empties.
·
Illustration continued on opposite page
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
613
Figure 7 (Continued). I and J, After 1 hour the leading edge of the barium column has
reached the colon. Most of the barium has been emptied from the stomach. K and L, After 2
hours much of the barium has entered the colon as barium passes through the small bowel.
A small amount of residual barium coating the gastric mucosa is a common occurrence.
Illustration continued on following page
614
WILLIAM
R.
BRAWNER.
JR.
AND jAN
E.
BARTELS
Figure 7 (Continued). M and N, After 4 hours
barium has cleared the small bowel.
exact time of gastric emptying varies but can be considered normal if there
is steady and uninterrupted progression of barium into the small bowel.
The intestine should appear as a continuous radiodense ribbon. The
duodenum is filled at 15 to 30 minutes. Much of the jejunum is filled at 1
hour, at which time there are many superimposed loops of bowel. The
leading end of the barium column usually reaches the cecum in 1Vz to 2
hours and much of the barium has entered the colon within 3 to 4 hours.
As noted above, a number of factors may affect the gastric emptying and
small bowel transit time. The uniform progression of barium through the
tract is a more important criterion of normal gastrointestinal motility than
is the exact transit time. In cats gastric emptying and transit time are more
rapid, with barium reaching the colon within 30 to 60 minutes (Fig. 8). 9
The stomach and intestines are in constant motion in the resting
animal. Gastric and intestinal movement can be observed fluoroscopically
but when a fluoroscope is not available, sequential radiographs allow
assessment of gastrointestinal dynamics. It is important to remember that
the films of an upper GI series represent a series of "stop-action" views of
a dynamic system. Figure 9 shows the varying shape of a dog's stomach in
three sequential radiographs. Annular contractions constantly progress from
the body of the stomach to the pylorus. The different shapes of the stomach
on sequential films occur because the "stop-action" views catch the contractions in different regions of the stomach. True anatomic abnormalities
cause either changes in the shape of the gastric or intestinal wall or loss of
contractility which will persist on sequential radiographs (Fig. 10).
If the progression of barium to the large bowel is delayed or if no
diagnostic radiographic signs are observed in the first 4 hours, the examination should be continued until all barium has cleared the small bowel.
In such cases it is useful to make a final radiographthe next morning (18
to 24 hours after administration of barium). The delay~d radiograph may
Text continued on page 618
CONTRAST RADIOGRAPHY OF THE DIGESTIVE Tl\ACT
615
Figure 8. Liquid barium suspension progresses more rapidly through the gastrointestinal
tract in cats than in dogs. A, Radiograph made 30 minutes after barium was given to a cat.
Notice that barium has already filled the ascending colon. This radiograph also demonstrates
two other characteristic features of the upper GI series in cats: the J-shaped stomach with
acute angulation of lesser curvature and position of pylorus near the midline; and the "string
of pearls" appearance of the duodenum created by multiple segmental contractions. B, After
90 minutes most of the barium has reached the colon. Notice that the cecum in the cat is
nonsacculated and appears as the tapered blind end of the ascending colon.
616
WILLIAM
R.
BRAWNER,
JR.
AND }AN
E.
BARTELS
Figure 9. A to C, Sequential radiographs of an upper gastrointestinal series in
a dog. The stomach is constantly contracting
during gastric empyting. The shape of the
stomach depends on the stage of contraction
at the instant of radiographic exposure.
These normal annular contractions should
not be mistaken for mass lesions of the
gastric wall.
ONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
617
Figure 10. Sequential radiographs of an upper gastrointestinal series at 10 minutes (A),
5 minutes (B), 30 minutes (C), and 45 minutes (D). Notice the asymmetric indentation at the
1teral aspect of the pyloric sphincter. True anatomic abnormalities are distinguished from
ormal contractions by asymmetry and by persistence on sequential films. The lesion in this
xample was a benign neoplasm. Notice.that there was pyloric outflow obstruction and that
~e dog vomited tbe barium between the 30- and 45-minute films.
618
•
WILLIAM
R. BRAWNER, JR. AND JAN E. BARTELS
Figure 11. Radiographs from an upper
gastrointestinal series of a dog with signs of
gastrointestinal obstruction. A, Thirty minutes after administration of barium, contrast
medium is seen emptying into the small
bowel. B, At 6 hours distended bariumfilled gut loops characteristic of obstructive
disease are seen but the site of obstruction
cannot be identified. C, On delayed radiograph at 20 hours (the next morning) the
barium clearly outlines an ileocolic intussusception in the cranial ventral abdomen.
show residual accumulation of barium in an absorbent foreign body (such
as a cloth or sponge) or may define a lesion in the distal small bowel or
colon not seen on earlier films (Fig. 11).
One should realize that upper GI studies frequently show no abnormalities. Many cases of chronic vomiting or diarrhea are caused by metabolic
disorders that do not cause anatomic abnormalities or dynamic changes
detectable by contrast radiography. Even when lesions are detected by
radiography, specific etiologic diagnosis may not be possible. Observation
and biopsy by endoscopy or laparotomy are often required for definitive
diagnosis. Although an upper GI series does not often provide a final
diagnosis, it does answer many significant questions: Is an anatomic lesion
present? Is the lesion mucosal, infiltrative, or extraluminal? Is the condition
obstructive or nonobstructive?
Complications resulting from an upper GI series are rare. Barium
leaking into the peritoneal cavity through an unsuspected perforation of the
stomach or small bowel is a potentially serious sequela. Aspiration of barium
can occur when it is being administered orally or when vomiting occurs
after administration. Barium in the trachea and bronchi is of little consequence, as it is removed by the natural action of cilia and the cough reflex
(Fig. 12A). In fact, barium is sometimes used purposely in performing
bronchograms. If barium reaches the alveoli, however, it cannot be removed
or absorbed and forms a local granulomatous reaction (Fig. 12B). If only a
small portion of lung is involved, the residual barium may cause no harm
(Fig. l2C). If a large volume of lung is flooded by!njstaken placement of a
stomach tube or aspiration of a large volume of barium, respiration may be
compromised sufficiently to cause permanent disability or death.
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
619
Figure 12. A , Barium aspirated into the trachea and
mainstem bronchi does not cause adverse sequelae. It is
removed by ciliary action and coughing. B, Barium aspirated into the alveoli is trapped and causes a granulomatous
reaction but ·is usually not fatal if only a small portion of
lung is affected. C, Residual barium granulomas caused by
aspiration during an upper GI series 5 years earlier; this is
an incidental finding not associated with clinical signs.
In summary, the upper GI series is a safe and effective diagnostic
procedure but one that requires careful planning and attention to proper
technique. The most important (and most often overlooked) technical factors
of a good barium series are as follows:
Prepare the patient well; cleanse the gastrointestional tract.
Use commercially-prepared liquid barium suspension.
Administer enough barium to distend the stomach.
Take an adequate number of radiographs.
Follow the study until a diagnosis is made or until barium clears the small
bowel.
Pneumogastrogram
A pneumogastrogram is performed simply by distending the stomach
with air. No sedation or anesthesia is required. A stomach tube is passed
and air is administered by dose syringe or with a bulb inflator until there
is slight abdominal tympany. Radiographs are made with the patient in
ventrodorsal, dorsoventral, and left and right lateral positions. A pneumogastrogram can be quickly and inexpensively performed as a screening
procedure for gastric foreign bodies or simply to identify the size, shape,
and position of the stomach (Fig. 13). Negative contrast techniques do not
allow good visualization of mucosal detail.
620
WILLIAM
R.
BRAWNER, }RAND }AN
E.
BARTELS
A
Figure 13. Lateral survey abdominal radiograph (A) of a dog showing an ill-defined
mineral density in the cranial ventral abdomen. A subsequent pneumogastrogram (B) shows
that the density is a gastric foreign body (bone) in the pyloric antrum. The stomach was
inflated with air by orogastric intubation.
Double-Contrast Gastrogram
The double-contrast gastrogram is indicated for careful evaluation of
the gastric mucosa. It should be considered when mucosal ulcerations or
mass lesions (neoplastic or inflammatory) of the gastric wall are suspected,
or when an upper GI series is indeterminate in animals with chronic
vomiting or hematemesis.
The patient must be prepared for radiography in the same manner
described for an upper GI series. Because the double-contrast study is not
used to evaluate motility, the animal may be sedated for the examination.
A stomach tube is passed and 1.1 to 3.3 ml per kg (0.5 to 1.5 cc per lb) of
barium suspension is administered and followed by a sufficient quantity of
air to distend the stomach. Just prior to administration of the contrast
material, glucagon may be given intravenously to induce hypotonicity and
hypomotility of the stomach and intestines. 2• 3 The distended stomach should
be radiographed in multiple positions to complete the study. Radiographic
projections should include at least the four standard gastric views and a left
dorsal oblique view.
CONTRAST EXAMINATION OF THE LARGE BOWEL
Barium Enema
The dog and cat both have a simple large bowel which may be divided
into the cecum; the ascending, transverse, and descending colon; and the
rectum. Large bowel disease is not common in small animals, but when it
occurs a barium enema is the radiologic examination of choice. Diseases of
the colon can rarely be identified on survey radiographs, and an upper GI
series does not usually allow adequate evaluation of the colon. Barium that
has progressed from the stomach is often desiccated to a semisolid state
when it reaches the descending colon and do~ot provide good mucosal
detail. The barium enema examination is indica d in cases of large bowel
diarrhea, suspected intussusception, and tenesm s or rectal bleeding when
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
621
a diagnosis cannot be made from survey radiographs and other clinical
information. Endoscopy is also an important technique in the evaluation of
large bowel disease. The cecum and the ascending and transverse portions
of the colon are often inaccessible to examination with rigid endoscopes,
but flexible fiberoptic endoscopes allow visualization of the entire large
bowel. Barium enema examination and endoscopy may be used as complementary procedures for thorough evaluation of the colon.
Stringent preparation of the colon is essential for both endoscopic
examination and barium enema. More thorough cleansing is necesssary for
this examination than for the upper GI series; all residual food material
should be removed from the large bowel, so the animal should not be fed
for at least 24 hours. Laxatives may be administered the day before and an
enema performed the evening before the examination. One to two hours
before the barium enema examination, repeated enemas should be given
until no additional food material is expelled.
General anesthesia is required for performing an adequate barium
enema examination. Awake or midly sedated animal patients cannot be
expected to cooperate when distention of the colon by barium initiates the
defecation reflex. Even if the patient can be physically restrained and
barium contained within the large bowel, there will be reflex contractions
of the colon which make interpretation of the contrast study difficult.
Survey radiographs should be obtained immediately before induction of
anesthesia to verify adequate preparation of the colon and to provide
baseline films for the contrast examination. If residual ingesta are present
in the colon, then further preparation is required.
The contrast medium of choice for retrograde large bowel examination
is the liquid barium suspension used for the upper GI series diluted 1:1
with warm water in an enema bag. Disposable plastic enema bags are ideal
for use in the barium enema procedure and are available as a prepackaged
unit with bag, plastic tube, tube clamp, and rectal catheter. When the
barium mixture is prepared, the enema bag is suspended from an intravenous stand. Barium is allowed to fill the tube so that air is displaced from
the system. A rectal catheter with inflatable cuff is placed in the patient's
rectum, and the cuff is gently inflated to lock the catheter into the pelvic
canal. Barium is administered by gravity flow at a dose of 11 to 13 ml per
kg (5 to 15 cc per lb). The exact dose is difficult to ascertain because the
diseased colon is often less distensible than normal and will accept a lower
volume of fluid . Ideally, the barium is administered under fluoroscopic
control so that the inflow of contrast medium can be observed and
discontinued when barium reaches the cecum. It is importaqt that barium
not be forced into the small bowel because contrast-filled small bowel loops
overlying the colon create an objectionable artifact on subsequent radiographs. In most veterinary practices a fluoroscope is not available. Under
such conditions, it is wise to administer barium at 11 ml per kg (5 cc per
lb) and then make a single ventrodorsal scout radiograph to evaluate the
degree of filling. If the colon is not completely filled then additional barium
can be administered.
•
Once the colon is filled with barium, radiographs should be exposed
in the left lateral, ventrodorsal, and left and right ventrodorsal-oblique
622
WILLIAM
R.
BRAWNER, JR. AND JAN
E. BARTELS
Figure 14. Lateral (A), ventrodorsal (B), right ventrodorsal oblique (C), and left ventrodorsal oblique (D) radiographic projections of a barium enema in a healthy adult dog. The
cecum, ascending colon, transverse colon, and descending colon can be identified. A small
amount of barium has refluxed into the terminal ileum. The redundant fold in the descending
colon is a normal variant. The right ventrodorsal oblique projection allows full visualization of
this fold, which is not well seen in the other projections. Note the smooth mucosal margins
of the colon.
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
623
projections (Fig. 14). The multiple projections show various profiles of the
colon and aid in locating. filling defects and irregularities of the colon wall.
The colon of the dog and cat is simple and nonsacculated, and exhibits
a smooth mucosal lining. Typically the overall shape is that of a shepherd's
crook, but additional flexures or folds may be present in many normal
animals. It is common for a reflex segmental contraction to be present just
cranial to the tip of the catheter and inflatable cuff.
Once the radiographs are developed and it is determined that no
retakes are necessary, barium may be emptied from the colon by removing
the enema bag from the intravenous stand and placing it below the level
of the radiographic table to allow barium to flow from the colon back into
the bag. A double-contrast procedure may then be performed. If doublecontrast examination is desired, care should be taken to remove as much
of the barium from the colon as possible by elevation of the dog's
forequarters and gentle palpation of the colon. Air is then insufflated into
the colon through the rectal catheter to provide moderate distention of the
colon. Left lateral, ventrodorsal, and left and right ventrodorsal oblique
radiographs are made. Radiographs made with double contrast show excellent mucosal detail with barium coating the mucosa of the air-filled colon
(Fig. 15).
Figure
detail. The
in a profile
coating (B),
15. The double-contrast barium enema procedure enhances visualization of mucosal
normal canine colon mucosa is smooth and regular. The barium coating appears
as a fine straight line (A). Mucosal irregularities cause spiculation of the barium
as seen in this double-contrast study of a dog with severe ulcerative colitis.
624
WILLIAM R. BRAWNER,
JR. AND }AN E.
BARTELS
In the procedures described above, the terminal (intrapelvic) colon
and rectum cannot be evaluated because of the presence of the rectal
catheter and inflatable cuff. If intrapelvic disease is suspected, the catheter
and cuff should be removed before the positive contrast radiographs are
made. If the colon has not been overfilled and the catheter is removed
gently, barium will not be expelled.
In puppies, kittens, and debilitated animals, which cannot be generally
anesthetized, some information can be gained by instilling barium directly
into the rectum and colon with a dose syringe.
Careful planning and attention to technique are necessary to achieve
a barium enema examination of optimal quality, but when indicated the
study can provide excellent diagnostic information. It has proved most
useful in differentiation of mucosal and transmural disease of the colon and
in evaluation of intussusception, cecal inversion, large bowel neoplasia, and
strictures.
Serious complications from the barium enema procedure occur when
there is perforation of the large bowel. If the clinical examination suggests
rupture, tear, or perforation of the rectum or colon, then barium sulfate
preparations should not be administered. Since the colon is distended with
barium in the barium enema, it is almost certain that barium will be forced
into the peritoneal cavity if a perforation is present. Water-soluble organic
iodine contrast medium may be administered rectally to evaluate the
integrity of the large bowel.
Care must also be taken to avoid iatrogenic perforation of the colon or
rectum during the procedure. The rectal catheter should be lubricated and
inserted gently. It is also important that the inflatable catheter cuff be
distended only enough to lock the catheter snugly into the pelvic canal.
Overinflation of the cuff may cause a colon or rectal tear, especially if the
tissue is diseased or devitalized.
The barium enema examination is often used in conjunction with
endoscopy, during which biopsy samples of the colonic mucosa and of
intraluminal lesions may be taken. The biopsy procedure is often essential
to definitive etiologic diagnosis, as radiographic examination and gross
visualization of the colon allow only description of the extent and nature of
the lesions. Many sources warn that a barium enema should not be
performed for 3 to 4 days after colonic biopsy to avoid the possibility of
extraluminal extravasation of barium at the site of biopsy. This creates
practical problems in veterinary medicine since the patient must be
anesthetized for both the endoscopic examination and barium enema. The
endoscopic examination cannot be performed immediately after a barium
enema because the barium obscures visualization of the colon mucosa. If 4
days are allowed to elapse between endoscopic examination and barium
enema then the animal must be generally anesthetized twice, causing
increased risk for the patient, a greater investment of time in diagnostic
procedures, longer hospitalization time, and increased client expense. We
have found that the barium enema can be safely performed immediately
after endoscopic examination and biopsy when such biopsies are superficial
and made with small biopsy forceps under fiberoptic visualization. No
CONTRAST RADIOGRAPHY OF THE DIGESTIVE TRACT
625
A
Figure 16. Normal pneumocolon. Lateral (A)
and ventrodorsal (B) radiographs of the abdomen
made after rectal instillation of air. The cecum and
all segments of the colon can be identified.
extravasation of barium has been observed under these conditions and no
adverse sequelae have occurred.
Pneumocolon
The pneumocolon is a safe and easy procedure that can be used to
ascertain the position of the colon when its location cannot be determined
from the presence of gas or ingesta on survey radiographs, and as a
screening procedure for large bowel obstructive disease. The procedure
does not require anesthesia or sedation. A 30- or 60-cc syringe is used to
instill air directly into the rectum and colon. The tip of the syringe is placed
in the anus and the front of the syringe barrel is pressed against the anus
to form a seal. Approximately 11 ml of air per kg body weight (5 cc per lb)
is usually adequate to yield moderate distention of the colon. Ventrodorsal
and left lateral radiographs are made immediately, before the air is expelled
(Fig. 16). This technique does not allow visualization of mucosal irregularities, but intraluminal masses or strictures of the large bowel can often be
located. Assessment of the nature and etiology of the lesion requires further
diagnostic procedures such as barium enema, endoscopy, or laparotomy.
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BARTELS
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Department of Radiology
School of Veterinary Medicine
Auburn University
Auburn, Alabama 36849