C-RADS CT Colonography Reporting and Data System version 2023

{
  "applicability": {
    "examination": "CT_colonography_screening_or_diagnostic",
    "current_release": "C-RADS_v2023",
    "classification_unit": "one_examination_with_one_overall_colorectal_C_category_and_a_separate_extracolonic_E_category",
    "prerequisites": [
      "interactive_2D_and_3D_review",
      "assessment_of_cleansing_distention_and_tagging",
      "complete_colonic_review_or_explicit_C0_limit"
    ]
  },
  "categories": [
    {
      "outcome_code": "C0",
      "state": "colorectal_assessment_not_confidently_possible",
      "triggers": [
        "technical_limitation_prevents_exclusion_of_a_polyp_10_mm_or_larger",
        "required_prior_study_not_available_for_comparison"
      ],
      "risk_state": "unassessable_not_low_risk"
    },
    {
      "outcome_code": "C1",
      "state": "normal_or_benign",
      "requirements": [
        "entire_colon_adequately_cleansed_and_distended",
        "no_polyp_6_mm_or_larger"
      ],
      "allowed_findings": [
        "diminutive_polyp_5_mm_or_smaller",
        "diverticula",
        "high_confidence_benign_myochosis_or_muscular_hypertrophy",
        "lipoma",
        "confident_residual_stool"
      ]
    },
    {
      "outcome_code": "C2a",
      "state": "one_or_two_small_polyps",
      "polyp_count": "1_or_2",
      "each_polyp_size_mm": "6_to_9_inclusive",
      "prior_code": "C2_in_the_2005_release"
    },
    {
      "outcome_code": "C2b",
      "state": "likely_benign_mass_like_diverticular_or_muscular_process",
      "findings": [
        "mass_like_diverticular_stricture",
        "moderate_or_severe_myochosis",
        "muscular_hypertrophy"
      ],
      "supportive_features": [
        "preserved_haustral_architecture",
        "no_3D_mucosal_irregularity",
        "diverticulosis",
        "lack_of_overhanging_edges_or_shoulders"
      ],
      "escalation": "if_clinical_index_of_concern_is_high_assign_C4"
    },
    {
      "outcome_code": "C3",
      "state": "polyp_or_subepithelial_lesion_requiring_colonoscopic_evaluation",
      "any_of": [
        "one_or_more_polyps_10_mm_or_larger",
        "three_or_more_polyps_each_6_to_9_mm",
        "unequivocal_interval_growth_of_a_prior_C2a_polyp",
        "subepithelial_lesion_10_mm_or_larger"
      ]
    },
    {
      "outcome_code": "C4",
      "state": "likely_malignant",
      "any_of": [
        "polypoid_mass_30_mm_or_larger",
        "malignant_appearing_mass_at_any_size"
      ]
    }
  ],
  "assignment_algorithm": [
    {
      "step": 1,
      "rule": "Assess cleansing, distention, tagging and segmental visibility; assign C0 when a confident colorectal interpretation is impossible or a required prior is missing."
    },
    {
      "step": 2,
      "rule": "Measure every reportable lesion, count 6-to-9-mm polyps, characterize morphology and reader confidence, and compare with priors using the same lesion."
    },
    {
      "step": 3,
      "rule": "Apply C4 before C3, then C2b or C2a, then C1, according to the most consequential colorectal finding; retain every raw lesion descriptor."
    },
    {
      "step": 4,
      "rule": "Assign and report the extracolonic E category independently; never use an E finding to replace the colorectal C category."
    }
  ],
  "measurement_and_reporting_protocol": {
    "reportable_polyp_threshold_mm": 6,
    "diminutive_rule": "Polyps 5 mm or smaller are generally nonreportable under the CTC framework, but technical or clinical context must not be silently discarded.",
    "size_rule": "Use the single largest diameter after 2D and 3D pitfall review; for a pedunculated polyp measure the head and exclude the stalk.",
    "required_lesion_fields": [
      "largest_diameter_mm",
      "measurement_method_and_series_or_image",
      "colon_segment_and_proximal_mid_or_distal_location",
      "sessile_pedunculated_or_nonpolypoid_morphology",
      "number",
      "reader_confidence_when_relevant"
    ],
    "location_rule": "Use rectum, sigmoid, descending, transverse, ascending or cecum; avoid flexure labels and colonoscope-distance crosswalks."
  },
  "decisive_boundaries": {
    "C0_versus_C2b": "A truly nondiagnostic collapsed or poorly prepared segment that cannot exclude a lesion of at least 10 mm is C0; a mass-like but likely benign diverticular or muscular segment with interpretable morphology is C2b.",
    "C2a_versus_C3_by_count": "One or two 6-to-9-mm polyps are C2a; three or more in that size band are C3.",
    "C2a_versus_C3_by_size": "Nine millimeters remains C2a when count permits; 10 mm is C3.",
    "C3_versus_C4": "A polyp or subepithelial lesion at least 10 mm is C3 unless it is a polypoid mass at least 30 mm or otherwise malignant appearing, which is C4."
  },
  "risk_interpretation": {
    "histology_limit": "CTC cannot determine dysplasia or histology; a C category is not a pathology result.",
    "C0_limit": "C0 supplies no neoplasia risk estimate because the colon is not adequately assessable.",
    "C2a_cohort_context": "Published surveillance cohorts found growth in 22 to 35 percent by 3 years and complete resolution in about 10 to 14 percent; these are cohort observations, not a probability for this patient's lesion.",
    "C3_context": "Polyps at least 1 cm have a reported 10 to 25 percent likelihood of high-grade dysplasia or carcinoma, varying with size; do not convert the range into individual certainty.",
    "C4_limit": "C4 means likely malignant on imaging, not proven cancer, TNM stage, resectability or prognosis."
  },
  "management_boundary": {
    "C0": "Repeat or complete CTC when visualization is inadequate, consider an alternative screening test, or amend the report when the missing prior becomes available.",
    "C1": "Routine CTC screening at 5 to 10 years, with any shorter interval justified by the full clinical and colonic context.",
    "C2a": "Repeat CTC in 3 years versus optional colonoscopy according to age, comorbidity, preference, local practice and confidence; unequivocal growth moves to C3.",
    "C2b": "High-confidence benign morphology may return at 5 years; lesser confidence supports 3 years or less; high concern is C4 with endoscopic evaluation.",
    "C3": "Recommend colonoscopic polypectomy; if it cannot be performed, CTC within 1 year or surgical referral may be appropriate according to anatomy, age and comorbidity.",
    "C4": "Recommend surgical and/or oncologic consultation with or without preoperative colonoscopic biopsy; do not infer a definitive operation from C4 alone."
  },
  "system_collision_boundary": {
    "legacy_C2": "The 2005 C2 code is retired in the current API. Use C2a for one or two 6-to-9-mm polyps and C2b for the new likely benign mass-like diverticular category.",
    "extracolonic_E_axis": "C and E are parallel outputs. In v2023, E1 and E2 are combined as E1/E2; E0 remains optional.",
    "optical_colonoscopy": "CTC size and segment descriptors must not be represented as histology or exact colonoscope distance."
  },
  "agent_output_contract": [
    "State C-RADS v2023 and whether the examination is screening or diagnostic.",
    "Report adequacy of cleansing, distention and tagging before assigning the C category.",
    "List each reportable lesion with size, method, segment, morphology, count and confidence; preserve the decisive lesion for the overall category.",
    "Return the active C code, the exact triggered rule, the linked follow-up options and patient-context qualifiers.",
    "Return the separate E category when available and never emit legacy C2 as a current result.",
    "Keep imaging suspicion, histology, cancer stage and individualized risk as separate facts."
  ],
  "missing_input_behavior": [
    "If adequacy is unknown, do not default to C1; return C-RADS_not_final and request cleansing, distention, tagging and segmental visibility.",
    "If a polyp size straddles 9 and 10 mm, preserve the measurement uncertainty and return C2a versus C3 rather than rounding silently.",
    "If the number of 6-to-9-mm polyps is incomplete, do not choose between C2a and C3.",
    "If a mass-like diverticular segment cannot be distinguished from malignant morphology, return C2b versus C4 with the missing features and recommend the appropriate resolving evaluation.",
    "If only C2 is supplied, identify it as legacy/ambiguous and request whether the intended current code is C2a or C2b."
  ],
  "supporting_sources": [
    {
      "role": "current_primary_release",
      "citation": "Yee et al. Radiology. 2024;310:e232007",
      "doi": "10.1148/radiol.232007"
    },
    {
      "role": "original_lineage",
      "citation": "Zalis et al. Radiology. 2005;236:3-9",
      "doi": "10.1148/radiol.2361041926"
    },
    {
      "role": "official_release_index",
      "citation": "American College of Radiology C-RADS current releases",
      "url": "https://cs.acr.org/Clinical-Resources/Reporting-and-Data-Systems/C-Rads"
    }
  ],
  "source_locator": "Yee et al. Radiology 2024, DOI 10.1148/radiol.232007, Table 2 and sections Reporting, Pitfalls of Lesion Measurement, Classification and Suggested Follow-up of Colonic Lesions, and Reporting of Extracolonic Findings; ACR C-RADS v2023 Summary of Changes."
}