Radiography: large intestine contrast

• Retrograde administration of positive, negative or a combination of contrast agents into the large intestine provides information about the intestinal lumen.

• Investigation of:
  • Tenesmus, eg colitis Colitis.
  • Large bowel diarrhea.
  • Hematechezia.
  • Suspected intussusception Intussusception.
  • Position of colon in relation to caudal abdomen/pelvic masses.
  • Suspected large intestinal obstruction, eg colonic mass.

Advantages

• Relatively simple procedure in most practices.
• Inexpensive.

Disadvantages

• Messy.
• Time consuming.
• May give limited information.

• Endoscopy Colonoscopy should precede barium study if doing procedure on same day.
• Ultrasonography (do not perform negative contrast study prior to ultrasonographic examination).

Preparation

• 15 min.

Procedure

• 20 min.

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 perforation of bowel water-based agent may be safer.

Minimum equipment

• X-ray machine.
• Cassette.
• Processing facilities.
• Protective clothing (lead apron) for radiographer.
• Positioning aids (sandbags, cradle and ties).
• Method of labeling film.
• Foley or colon retention catheter.
• Enema pump or infusion tubing with large volume syringe.

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.

Minimum consumables

• Radiographic film.
• Contrast agent.
• Water-soluble lubricant for catheter.

• Withhold food for 12-24 hours before procedure.

• General anesthesia usually required.
• Pneumocolon can be performed to identify the position of the colon without sedation.

• Large bowel must be completely emptied of feces the night before the procedure.
• Administer cleansing enema Enema the night before and repeat at least 2-3 hours before study.
• Enema should be repeated until no residual material in colon.
  Laxatives given the day before the procedure may help.

Choice of contrast study

• Positive, negative or double contrast studies can be performed.
  Double contrast study should be performed after positive contrast study.
• Positive contrast and double contrast studies allow evaluation of mucosal detail.
• Pneumocolon useful to identify position of colon and intraluminal masses, eg intussusceptions or strictures.
• Positive contrast:
  • Liquid barium suspension can be diluted with warm water/saline to 20% w/v.

Step 1 - Control Films

• Lateral abdominal radiograph Radiography: abdomen:
  • Check exposure settings and processing.
    Increase KV by 6-8 if performing positive contrast study.
  • Confirm positioning adequate.
  • Confirm diagnosis not apparent without contrast study.

Step 2 - Prepare barium

• Prepare barium by adding water.

Step 3 - Insert catheter

• Insert lubricated catheter into rectum.
• May need purse string suture in anus, if balloon or colon retention catheter of sufficient size is not available.

Step 1 - Administer contrast

Pneumocolon

• Inject air 1-3 ml/kg to fill colon.

Positive contrast

• Insert Foley or colon retention balloon catheter into anus and inflate bulb.
• Inject contrast (11-13 ml/kg) slowly using large syringe.
  Alternatively use enema pump or fluid infusion and funnel may be used with contrast administered under gravity.

Double contrast study

• To perform double contrast study inject positive contrast agent then remove and perform pneumocolonogram.

Step 2 - Obtain radiographic views

• Lateral, ventrodorsal and right and left lateral ventrodorsal oblique views should be taken.

Step 1 - Assess radiographs

• Normal colon has smooth mucosal surface on lateral and ventrodorsal views.
• After administering 10 ml/kg can take radiograph to check not overdistending bowel .
• Contrast entering small intestine may hinder interpretation.
• Add more contrast if necessary.

Step 2 - Remove catheter

• Remove catheter.

Potential complications

• Iatrogenic rupture of colon - avoid by using lubricated catheter and not over-inflating Foley catheter cuff.

• Inadequate contrast administration.
  Diseased colon is often more distensible than normal bowel so take radiograph to assess filling and then add more contrast if necessary.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Nyland T G & Ackerman N (1978) Pneumocolon - a diagnostic aid in abdominal radiography. J A Vet Radiol Soc 19 (6), 203-209 VetMedResource.

Other sources of information

• Thrall D E (1998) The Textbook of Veterinary Diagnostic Radiology. 3rd edition. pp 560-570.
• Brawner W R & Bartels J E (1983) Contrast radiography of the digestive tract. Vet Clin North Am 3, 599-626.