CT colonography reporting and data system

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

Terminology

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 tumours

  • 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:

  • rectum

  • sigmoid colon

  • descending colon

  • transverse colon

  • ascending colon

  • caecum

Classification

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

Colonic classification

• C0: inadequate study and/or awaiting prior comparisons

  • inadequate preparation: fluid or faeces 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

Extra-colonic classification

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

Treatment and prognosis

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

Practical points

• 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