Radiography: gastrography

• Use of positive, negative or a combination of contrast agents to highlight the gastric lumen.

• Identification of the position of the stomach, eg in ascites or if suspect gastric displacement, eg diaphragmatic hernia Diaphragm: traumatic hernia.
• Investigation:
  • Vomiting Vomiting or hematemesis.
  • Melena.
  • Suspected radiolucent foreign bodies Stomach: foreign body.
  • Abdominal pain or distension.
  • Inappetance.
• Assessment of lumen size and gastric axis if stomach not visible on plain films.

Advantages

• Relatively simple procedure in most patients.
• Non-invasive.

Disadvantages

• Often difficult to assess subtle mucosal lesions.
• Not very accurate for assessment of motility disorders.

• Difficult to interpret if not familiar with normal appearance.

• Gastric ultrasonography (should precede contrast radiography if performed on same day).
• Gastroscopy Gastroscopy (should precede contrast radiography if performed on same day,although drugs used for restraint will affect gastric motility).
• Scintigraphy.
• Barium impregnated polyurethane spheres (BIPs).

Preparation

• Dependent upon method of restraint.
• Food withheld for 12-24 hours (may not be required if animal is inappetant).
• Enemas required ideally night before but not within 2-3 hours of procedure.
• May need to withhold food for 24 hours if delayed gastric emptying.
• If considering endoscopy Gastroscopy this should be performed before contrast radiography.

Criteria for choosing test

• Is the examination appropriate?
• Can you make the diagnosis without it?
• Will your management of the case be affected by the outcome of the examination?

Risk assessment

• If suspect gastrointestinal tract rupture it is theoretically safer to use water-soluble contrast agents:
  • Gastrointestinal tract rupture requires surgical intervention and abdominal lavage so leakage of contrast agents may not be a particular problem and iodine-based agents may exacerbate hypovolemia in a shocked animal by drawing fluid into the GI tract.

Minimum equipment

• X-ray machine.
• Cassette.
• Processing facilities.
• Protective clothing (lead apron) for radiographer.
• Positioning aids (sandbags, cradle and ties).
• Method of labelling film.
• Large syringe.
• Means of keeping mouth open for stomach tubing, eg inner part of bandage roll.
• Stomach tube.

Ideal equipment

• Ability to process films during procedure so that repeat radiographs can be taken during course of study if required.
• High output x-ray machine.
• High definition screen.
• Grid for examination of large dog.
• Mouth gag.

Minimum consumables

• Radiographic film.
• Contrast agent.
• Water-soluble lubricant for stomach tubing.

• Withhold food 12-24 hours prior to procedure.

• Sedation.
• Low dose of acepromazine Acepromazine maleate (0.05-0.1 mg/kg) has minimal effect of gastrointestinal motility and transit times.
  Avoid diazepam Diazepam , xylaxine Xylazine , barbituates, opoids and parasympathic drugs, eg atropine Atropine , as they have been shown to delay gastric emptying.
• If performing negative or double contrast studies gastric motility can not be assessed so effect of sedation is unimportant.

• Administer cleansing enema Enema the night before procedure and 2-3 hours before procedure if necessary.
• Glucagon has been used to promote gastric relaxation for double-contrast gastrography, but is very expensive.

Step 1 - Control films

• Plain abdominal radiographs Radiography: abdomen should be obtained prior to contrast study to:
  • Check exposure settings and processing.
  • Confirm animal adequately prepared, ie colon empty.
  • Confirm positioning adequate.
  • Confirm diagnosis not apparent without contrast study.
  • Identify radiopaque foreign bodies which may be masked by barium.
• Premeasure stomach tube against animal from mouth to stomach, and mark on tube length required to reach stomach.

Step 2 - Selection of contrast agent

• Positive:
  • Liquid barium (10 ml/kg,15% W/W).
  • Iodine-based contrast (2.2 ml/kg, 10% W/W) (hyperosmolar and may cause hypovolemia and shock. Expensive).
  • Suitable for assessing position of stomach, wall thickness and gastric emptying.
  • May mask foreign bodies.
  • Can be used for follow through investigation of small intestine.
• Negative:
  • Air (4-8 ml/kg).
  • Carbon dioxide/air.
  • Suitable for assessing position of stomach and identifying foreign bodies and gross wall thickening.
• Double contrast: provides best information on mucosal detail.

Step 3 - Insert stomach tube

• Insert premeasured length of stomach tube to level of stomach.
• Inject small amount of water/saline to ensure tube correctly placed in stomach and not respiratory tract.

Step 1 - Instil contrast agent

• Inject (negative or positive) contrast in sufficient quantity to distend stomach.
  Tendency to underfill stomach in most cases.
• Dose 5-12 ml/kg (with reduced dose rate for larger dogs).

• Administer 1-3 ml/kg of barium - lower doses for larger dogs.
• Roll animal through 360° then restomach tube and inflate stomach with air/carbon dioxide 5-10 ml/kg.
• Glucagon may be given prior to administration to allow maximum distension of stomach.

Step 2 - Obtain radiographic views

• Withdraw stomach tube before radiography.
• See abdominal radiography Radiography: abdomen for details of positioning.
• Immediately take DV, VD, left and right lateral projections.
• Repeat after 5-10 min.
• If abnormality seen make sure it is consistent on several films/views.
• If barium alone has been used a follow through study of intestines can be performed.
  This is not possible if negative or double contrast study performed.

Step 1 - Assess radiographs

• Ensure stomach adequately distended for interpretation.
• Stomach contractions may mimic pathology, including mural thickening and stenosis - if in doubt repeat radiograph.
• If barium is administered when food is still present in stomach this may mimic pathological filling defects.

Step 2 - Additional radiographic projections

• Follow up film at 24 hours may be useful for demonstrating retention of barium in stomach, eg foreign body or ulceration.
• If trying to identify position of stomach take lateral and VD views at 30-40 min when barium is in stomach and small intestine.
• Double-contrast views give superior mucosal detail, this is the best procedure to identify a gastric ulcer but views are often difficult to interpret.

Potential complications

• Aspiration of barium either during administration or after procedure if patient vomits.

• Inadequate patient preparation, ie stomach not empty.
• May not identify mucosal lesions or motility disorders.
• Poor gastric distension.
• Failure to obtain sufficient radiographs - lesion must be consistent on several films for diagnosis to be made.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Miyabayashi T & Morgan J P (1991) Upper gastrointestinal examinations - a radiographic study of clinically normal beagle puppies. JSAP 32 (2), 83-88 VetMedResource.
• Evans S M (1983) Double versus single contrast gastrography in the dog and cat. Vet Radiol 24 (1), 6-10 VetMedResource.
• Evans S M & Laufer I (1981) Double contrast gastrography in the normal dog. Vet Radiol 22 (1), 2-9 Wiley Online Library.

Other sources of information

• Hall J A & Watrous B J (2000) The effect of pharmaceuticals on radiographic appearance of selected examinations of the abdomen and thorax. Vet Clin North Am S A Pract 30 (2), 349-377, vii PubMed.
• Brawner W R Jr. & Bartels J E (1983) Contrast radiography of the digestive tract. Indications, techniques, and complications.​ Vet Clin North Am S A Pract 13 (3), 599-626 PubMed.

• American College of Veterinary Radiology, Executive Director: Dr M Bernstein, PO Box 87, Glencoe, IL 60022, USA. www.acur.ucdavis.edu.