C-RADS - reporting system for CT colonography

In July 2005, Radiology published a consensus proposal for reporting in CT colonography. It has similar purpose and structure as Bi-RADS reporting system in breast imaging. According to this proposal, lesions and massess should be describes by:

  • Lesion size: the largest dimension (excluding stalk in pedunculated polyps) measures on MRP or 3D views.
  • Morphology:
    • Sessile: broad-based with height > width
    • Pedunculated: polyp with a stalk
    • Flat: polyp with height < 3mm above the surrounding mucosa
  • Location: defined by six standard colonic segments: rectum, sigmoid, desceding, transverse, ascending colon, and cecum
  • Attenuation: CT density expressed as
    • Soft tissue
    • Fat

Categorization of colonic findings

Category Description
C0 Inadequate study or awaiting prior study for comparison
  • inadequate preparation, where lesions ≥10mm can not be excluded due to abundant fluid or feces
  • inadequate insufflation with one or more colonic segments collapsed on both views
  • awaiting prior study for comparison
C1 Normal colon or benign lesion - continue routine screening
  • no abnormality of the colon found
  • no polyp ≥6mm
  • non-neoplastic findings - diverticula, inverted diverticulum, lipoma, etc.
C2 Intermediate polyp or indeterminate finding - surveillance or colonoscopy recommended
  • <3 polyps 6 - 9mm
  • indeterminate finding where polyp ≥6mm can not be excluded despite technically adequate exam
C3 Polyp, possibly advanced adenoma - follow-up colonoscopy recommended
  • polyp >=10mm
  • ≥3 polyps 6 - 9mm
C4 Colonic mass, likely malignant - surgical consultation recommended
  • lesion compromises colonic lumen
  • extracolonic invasion

Categorization of extracolonic findings

Category Description
E0 Limited exam - compromised by artifacts, severly limited evaluation of extracolonic soft tissues
E1 Normal exam or anatomic variant - no extracolonic pathology found
  • ureter fissus, retroaortic renal vein as anatomic variants, etc.
E2 Clinically unimportant finding - no workup indicated
  • simple cysts in liver or kidney
  • uncomplicated cholecystolithiasis (gallstones)
  • vertebral hemangioma, etc.
E3 Likely unimportant finding, incompletely characterized - workup may be indicated based on local practice and patient preference
  • minimally complex or homogeneously hyperattenuating kidney cysts, etc.
E4 Potentially important finding - further workup according to accepted practice guidelines
  • solid renal mass
  • lympadenopathy
  • aortic aneurysm
  • parenchymal nodule in lung ≥=1cm, etc.


1. Zalis ME, Barish MA, Choi JR, Dachman AH, Fenlon HM, Ferrucci JT, et al. CT Colonography Reporting and Data System: A Consensus Proposal. Radiology. 2005 Jul 1;236(1):3–9.
2. Summers RM. Polyp Size Measurement at CT Colonography: What Do We Know and What Do We Need to Know? Radiology. 2010 Jun;255(3):707–20