For a patient with a colonic mass found on a CT scan without contrast, should I refer them to a GI specialist for a colonoscopy and repeat CT scan with and without contrast?

Management of Colonic Mass Found on CT Without Contrast

For a patient with a colonic mass found on CT without contrast, you should refer to GI for colonoscopy and there is no need to repeat the CT with contrast unless there are specific indications for staging. 1

Diagnostic Approach for Colonic Mass

• CT colonography (CTC) is effective for evaluation of the colon when a mass is identified, but colonoscopy remains the gold standard for direct visualization and biopsy of colonic lesions 1
• When a colonic mass is identified on routine CT without contrast, the next appropriate step is referral for colonoscopy rather than repeating the CT with contrast 1
• Colonoscopy allows for direct visualization, biopsy, and potential removal of the mass, providing definitive diagnosis 1

Rationale Against Routine Repeat CT with Contrast

• Standard CT abdomen and pelvis (not CTC protocol) has moderate effectiveness for detecting invasive carcinomas with a sensitivity of 72.4%, but is less sensitive for polyps (14.5%) 1
• Repeating CT with contrast is not routinely recommended unless there are specific indications for cancer staging or evaluation of extracolonic findings 1
• The American College of Radiology does not recommend routine CT with and without contrast for evaluation of colorectal masses, as it provides limited additional diagnostic value compared to colonoscopy 1

Indications for Repeat CT with Contrast

• Consider repeat CT with contrast only in specific scenarios:
  • When colonoscopy is contraindicated or not feasible 1
  • For evaluation of the colon proximal to an obstructing lesion 1
  • For staging if colorectal cancer is confirmed by colonoscopy 1
  • When extracolonic findings on initial CT require further characterization 1, 2

Clinical Algorithm

1. First step: Refer to gastroenterology for colonoscopy 1

   • Colonoscopy allows for direct visualization, biopsy, and potential removal of the mass
   • Provides definitive diagnosis with histopathological confirmation

2. Second step: Based on colonoscopy findings:

   • If benign polyp: Follow appropriate surveillance guidelines 1
   • If malignant: Proceed with staging CT with IV contrast 1
   • If colonoscopy is incomplete due to obstruction: Consider CT colonography 1, 3

Important Caveats

• Be aware that perforated colon cancer can mimic diverticulitis on imaging; CT findings suggesting cancer include pericolonic lymphadenopathy >1cm in short axis 1
• CT colonography has few contraindications but should not be performed when there is risk of perforation 1
• Extracolonic findings are common on CT scans (24% of cases) and may require additional follow-up 2
• For patients with suspected colorectal cancer, CT colonography has shown a positive predictive value of 90.9% for masses (≥20mm) but lower predictive values for smaller polyps 3

By following this approach, you will ensure appropriate diagnostic evaluation while avoiding unnecessary imaging studies that add radiation exposure without significant diagnostic benefit.