CT colonography reporting and data system

Last revised by Henry Knipe on 20 Apr 2024

CT Colonography Reporting and Data System (C-RADS) is a method for standardizing CT colonography (CTC) reporting. The current revision is 2023 5.

A polyp is defined as a homogenous soft tissue attenuation lesion projecting into the colonic lumen with a fixed point of attachment to the wall. Polyps at CTC are typically ≥6 mm or larger 5.

A mass is defined as a lesion measuring ≥30 mm and should not be described as a polyp 5.

Recommended descriptors of a colonic lesion at CTC include 5:

  • attenuation

    • soft tissue

    • fat (lipoma, fibrolipoma, inverted diverticulum)

  • morphology

    • sessile (broad-based)

    • pedunculated (polyp with separate stalk)

    • flat or laterally spreading tumors

    • mass (≥30 mm)

  • size (single largest dimension)

    • large (≥10 mm)

    • small (6-9 mm)

    • diminutive (≤5 mm)

      • not typically reported

      • much more likely to represent adherent stool, hyperplastic polyp (no malignant potential) or tubular adenomas

  • location - six standard colonic segments:

Abnormalities are classified into colonic (C) and extra-colonic (E).

  • C0: inadequate study and/or awaiting prior comparisons

    • inadequate preparation: fluid or feces obscures exclusion of lesions ≥10 mm

    • inadequate insufflation: one or more colonic segments collapsed on both views

  • C1: normal colon/benign lesion

    • continue routine screening

      • no abnormality

      • no polyp ≥6 mm

      • lipoma, inverted diverticulum or other non-neoplastic findings

  • C2a: indeterminate polyp or indeterminate finding

    • repeat CTC in 3 years or colonoscopy

      • 6-9 mm polyp

      • <3 in number

  • C2b: likely benign diverticular finding

    • likely benign: repeat CTC in 5 years, or;

    • uncertain benign: repeat CTC in 3 years

      • mass-like area such as diverticular mycosis coli, muscular hypertrophy or structure

  • C3: possibly advanced adenoma

    • follow up colonoscopy

      • polyp ≥10 mm

      • ≥3 polyps 6-9 mm size

  • C4: likely malignant colonic mass

    • colonoscopy, surgical and/or oncology referral

      • polypoid or malignant-appearing mass ≥30 mm

      • lesion compromises bowel lumen or extra colonic invasion

The purpose of CTC is to identify pre-malignant or malignant colonic lesions. The extra-colonic classification aims to simplify communication of incidental findings external to the colon. Since the original 2005 version, the updated 2023 version has reduced the number of categories from 5 to 4, combining E1 and E2, with reporting of E0 now optional 5.

  • E0: examination inadequate for assessment

    • reporting of this category is optional

  • E1/E2: no clinically important, or stable previously known extra-colonic findings, not requiring further work-up

  • E3: likely clinically unimportant finding; further work-up may be warranted

  • E4: likely clinically important finding; further work-up needed

Suggested management 5:

  • diminutive polyps (≤5 mm)

    • risk of advanced adenoma is 1.7%

    • CTC guidelines do not mandate reporting of this size as non-reporting has been found to be cost-effective and safe

  • small polyps (6-9 mm)

    • risk of advanced adenoma is 6.6%

    • polypectomy is suggested for patients who are candidates for colonoscopy

    • in patients with 1-2 small polyps, follow-up at 3 years is also an option depending on age and comorbidities

  • large polyps (≥10 mm)

    • risk of advanced adenoma is 30.6% with increased rates of high-grade dysplasia (5-10%) and carcinoma (1-3%)

    • referral for colonoscopy and polypectomy is recommended

  • masses (≥30 mm)

    • sensitivity and specificity of CTC for detection of colonic masses approaches 100%

    • referral for colonoscopy or directly to surgery or oncology is recommended

  • screening interval

    • 5-year screening interval is recommended by the American Cancer Society and the United States Preventative Task Force

    • 5-year screening interval is shown to be comparable to colonoscopy

  • evaluation using both 2D and 3D reconstructions are recommended to improve polyp detection 5

    • 2D imaging includes traditional multiplanar reconstructions

    • 3D reconstructions could include endoluminal perspective, anatomic dissection views, perspective filet or unfolded cube

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