What is the best imaging test to rule out colon cancer in a 63-year-old female with daily frank bright red blood per rectum (BRBPR), fecal incontinence, and abdominal pain who refuses colonoscopy?

CT Colonography is the Best Imaging Test for Ruling Out Colon Cancer in a Patient Refusing Colonoscopy

For a 63-year-old female with daily frank BRBPR, fecal incontinence, and abdominal pain who refuses colonoscopy, contrast-enhanced CT colonography after bowel cleansing is the best imaging test to rule out colon cancer. 1

Rationale for CT Colonography

CT colonography (virtual colonoscopy) offers several advantages in this high-risk patient:

• The Chinese Society of Clinical Oncology (CSCO) 2024 guidelines specifically recommend contrast-enhanced abdominal/pelvic CT scan after bowel cleansing for patients who refuse colonoscopy 1
• CT colonography has replaced double-contrast barium enema as the test of choice for colorectal imaging for nearly all indications 1
• CT colonography has high sensitivity (82-92%) for adenomas ≥1 cm in size 1
• It can visualize the entire colon, which is crucial given the patient's symptoms suggest a potential colorectal malignancy

Clinical Considerations in This Patient

This patient presents with several concerning features:

• Daily frank bright red blood per rectum (BRBPR)
• Fecal incontinence
• Abdominal pain
• Age 63 (increased risk for colorectal cancer)

These symptoms collectively suggest a high pre-test probability for colorectal pathology, potentially including cancer. The long-standing nature of symptoms does not reduce concern, as colorectal cancers can cause chronic bleeding.

Alternative Testing Options (Less Preferred)

1. FIT-fecal DNA test:

   • While this is a tier-2 screening option 2, it is not appropriate for diagnostic evaluation in a symptomatic patient with frank bleeding
   • Not recommended for patients with high-risk disease symptoms 1

2. Flexible sigmoidoscopy:

   • Limited evaluation of only the distal colon
   • May miss proximal lesions
   • Less comprehensive than CT colonography

3. Barium enema:

   • Inferior to CT colonography in sensitivity and patient tolerance 1
   • Has largely been replaced by CT colonography

Implementation Considerations

• The patient will need bowel preparation similar to colonoscopy
• Radiation exposure is a consideration but justified given the clinical scenario
• Incidental extracolonic findings are common and may require additional workup
• If lesions ≥6 mm are found on CT colonography, the patient should be strongly encouraged to reconsider colonoscopy for biopsy 1

Pitfalls and Caveats

• CT colonography has lower sensitivity for flat lesions and serrated polyps compared to colonoscopy 1
• Sensitivity for polyps <1 cm is less than colonoscopy 1
• The patient should understand that if a suspicious lesion is identified, colonoscopy will still be necessary for tissue diagnosis
• Patients with high-risk symptoms (like this patient) would ideally undergo colonoscopy, and this should be emphasized despite offering CT colonography as an alternative

Follow-up Recommendations

If CT colonography is negative, the patient should still be evaluated for other causes of her symptoms, particularly the fecal incontinence which may require specialized testing of anorectal function.

If CT colonography identifies any suspicious lesions, renewed efforts should be made to convince the patient to undergo colonoscopy for definitive diagnosis and possible intervention.