Preliminary Diagnosis: Colorectal Cancer

I. What imaging technique is first-line for this diagnosis?

CT colonography (CTC) has emerged as the leading imaging technique for colorectal cancer screening and it has similar diagnostic yield to colonoscopy.

II. Describe the advantages and disadvantages of this technique for diagnosing colorectal cancer.

Advantages
  • Less invasive than colonoscopy, with lower risk of perforation.
  • No sedation required.
  • Preferred over colonoscopy in coagulopathic patients or patients with respiratory disease.
  • Increased patient comfort.
  • Provides complete visualization of the colon.
  • Can detect extracolonic pathology.
  • Takes less time than colonoscopy or barium examinations.
Disadvantages
  • May not be reimbursed by some insurance companies.
  • If a suspicious lesion is seen, colonoscopy is needed to perform a biopsy.
  • Requires specialized reader training.
  • Exposure to ionizing radiation.
  • The ability to differentiate stool and artifact from small polyps may not be as good as conventional colonoscopy.

III. What are the contraindications for the first-line imaging technique?

  • Contraindicated in patients with active inflammatory bowel disease or diverticulitis because of increased risk of perforation.
  • Contraindicated in pregnant patients, who should not undergo CT scans.

IV. What alternative imaging techniques are available?

  • Double contrast (air contrast) barium enema (DCBE).
  • Single contrast barium enema (SCBE).
  • Conventional CT chest, abdomen, and pelvis with contrast or whole body FDG PET-CT are used for staging.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing colorectal cancer.

Double contrast (air contrast) barium enema (DCBE)
Advantages
  • DCBE Q5 years in combination with fecal occult blood testing is an appropriate screening method for patients who are unable or unwilling to undergo colonoscopy or CTC. Diagnostic yield can be supplemented by combining with sigmoidoscopy.
  • Best test if CTC or colonscopy cannot be performed.
  • Cost-effective.
  • Less risk of perforation.
  • Multiple images are acquired of the entire colon in orthogonal projections under the direction of the performing radiologist.
  • Best for polyps >1cm (82-98% sensitivity).
Disadvantages
  • Patient must be sufficiently mobile to rotate body on flouroscopy table.
  • If suspicious lesion is seen, further evaluation with colonscopy and biopsy may be required.
  • Operator dependent.
  • Less sensitive for polyps <1cm (<50% detection).
Single contrast barium enema (SCBE)
Advantages

Can be performed in patients unable to tolerate the double contrast exam.

Disadvantages
  • Less sensitive than double contrast exam.
  • Operator dependent.

VI. What are the contraindications for the alternative imaging techniques?

Double contrast barium enema (DCBE)
  • Contraindicated in patients with suspected bowel perforation.
  • Patients with limited mobility should not undergo DCBE.
Single contrast barium enema

Contraindicated in patients with suspected bowel perforation.

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