Colonography

Colonography refers to radiographic imaging of the large intestine. CT colonography is the modality most frequently used. Colonoscopy is used more often than colonography for evaluation of the large intestine, as it allows for taking biopsy samples and removing polyps during the same procedure.

Indications

• Lower gastrointestinal bleeding
• Screening for colorectal cancer
• Rectal atresia (Wangensteen-Rice x-ray is used)
• Abdominal abcess
• Inflammatory bowel disease
• Colonic polyps

Modalities

CT colonography

CT colonography with insufflation of the large intestine with CO2 is also called virtual colonoscopy or CT colonoscopy. It avoids the uncomfortableness of a regular colonoscopy but does not allow for sampling or treatment, and so colonoscopy is usually preferred instead.

Colonic transit study

A colonic transit study can be used to evaluate constipation. It involves the patient swallowing a capsule containing many small radiopaque markers. Serial radiographs are then taken, allowing one to visualise the movement of the markers over time.

Barium enema

Barium may be administered rectally, in which case the examination is called a barium enema. This is rarely performed.

Defecography

Defecography is a rarely used procedure used to evaluate for constipation. The rectum is filled with barium paste, and the patient defecates during fluoroscopic examination.

Patient preparation

Emptying the bowel before colonography is essential. The patient must fast minimum 6 hours ahead and only consume clear fluids (water and thin drinks) the day before. A strong laxative must be given to empty the bowel completely.

Interpretation

In cases of colorectal cancer which forms a stenosis, the apple core sign can be seen. This is an annular constriction of the colonic lumen which looks like an apple-core.

In case of colitis, the bowel wall is thickened and the bowel lumen is irregularly narrowed.