Enteric contrast medium (CT)

Enteric contrast media can be given to patients before their CT exam to improve its diagnostic accuracy. Historically, a combination of oral and intravenous contrast media were always given prior to a CT abdomen. Contemporaneously, improved CT scanners mean that oral contrast agents are no longer routinely used but remain in widespread use for a narrower range of indications.

Indications

Enteric contrast is usually given when the following are suspected ¹:

• postsurgical bowel leaks
• GI fistulae
• interloop fluid collections 
• CT colonography

Contraindications

Enteric positive contrast media is usually avoided in the following:

• CT enterography (neutral contrast media may be given)
• suspected mesenteric ischemia
• suspected GI bleeding: may obscure the acute blood/contrast leak
• CT abdominal angiography
• acute blunt trauma
• urolithiasis
• aspiration risk (relative contraindication)

Technique

Routes

CT enteric contrast media are most commonly administered by mouth, although may also be given by way of an enteric catheter (e.g. nasoenteric, PEG, etc.), via a stoma (e.g. ileostomy) or per rectum.

Preparation

It is important that luminal contrast medium, when used for CT, is appropriately diluted (~5-10%) (cf. fluoroscopy when neat contrast is used).

Water-soluble contrast agents are generally preferred to avoid the risk of chemical peritonitis, that may occur when barium sulfate contrast medium leaks into the peritoneal cavity.

Neutral contrast media

In some patients, it is helpful to give a neutral contrast agent, e.g. water, to distend the stomach/bowel and make it easier to see the stomach/bowel wall. This is particularly helpful if there is a clinical concern of bowel ischemia. Neutral oral agents may also be used for CT enterography.

Timing

The timing of administration of the contrast media is also clearly important. If given too long before (or too close to) the time of the CT examination then it may have already passed by (or not yet reached) the area of interest. There is a certain art to getting the timing right as speed of bowel transit varies considerably, especially in disease states.