Strategies for the Standardization and Documentation of Findings
To improve and standardize the clinical communication of results of CT colonography, in 2005 the Working Group on Virtual Colonoscopy in the United States introduced the C-RADS—the CT Colonography Reporting and Data System. In 2012 the European Society for Gastrointestinal and Abdominal Radiology (ESGAR) issued a consensus statement on CT colonography, also giving recommendations on reporting. Along with various other radiological societies, the American College of Gastroenterology has also made recommendations for the follow-up of polyps. Whichever is followed, the type of report and the documentation required should be selected with full knowledge of the methodological limitations of CT colonography and in consensus with the referring clinician.
ESGAR Consensus Statement on the Documentation of Colonic Lesions
The following section includes excerpts from the revised consensus statement by the European Society for Gastrointestinal and Abdominal Radiology (ESGAR) (Neri et al. 2012). The following recommendations on the documentation of colonic lesions were given:
Polyps. All polyps 6 mm or larger should be reported in both asymptomatic and symptomatic individuals.
CT colonography has limited diagnostic value for lesions less than 6 mm. However, if detected with high confidence, such lesions may be reported (particularly if ≥3 mm), in both asymptomatic and symptomatic individuals.
Extracolonic findings. The extracolonic organs should be assessed and abnormalities reported, noting the limitations if a noncontrast and/or low-dose technique was used.
C-RADS—CT Colonography Reporting and Data System
The aim of this system, introduced in 2005 by the Working Group on Virtual Colonoscopy, was to improve the structure and reproducibility of CT colonography findings, enhance the communication of findings, and ensure appropriate patient management. It was also intended to help decision-making about follow-up surveillance and colonoscopic polypectomies. The C-RADS classification was developed by reference to the BI-RADS classification which is used for mammography. The C-RADS classification was developed by radiologists and gastroenterologists in collaboration with the American College of Radiology and other specialized medical organizations. This system is increasingly used in routine diagnosis.
Morphological Description of Colonic Lesions
The primary focus of the C-RADS classification is on advanced adenomas 10 mm in size or larger. The goal is to achieve a standardized description of colonic pathologies. This description includes the size, morphology, segmental location, and CT density of the lesion (see Table 5.1).
Classification of Findings in the Colon and Recommended Follow-Up
The C-RADS classification refers to both the size and the number of intracolonic lesions. According to the Working Group on Virtual Colonoscopy, the clinical relevance of lesions 5 mm in size or smaller is limited. Including them in the report would lead to a rise in the number of false-positive diagnoses and many unnecessary colonoscopies. For this reason, 6 mm is suggested as the minimum size for reporting polypoid lesions in the C-RADS scheme.
Follow-up. The majority of lesions measuring 6–9mm in diameter are benign; 30% of them are not adenomas. There is a less than 1% risk that a lesion of this size is malignant. Accordingly, C-RADS recommends that in patients with no known risk factors for colorectal carcinoma (no positive family history and no history of carcinoma), follow-up should be performed if one-to-two lesions measuring 6–9 mm are detected. Follow-up should be by CT colonography or optical colonoscopy within 3 years.
Polypectomy or surgery. Patients with three or more polyps larger than 6 mm have an increased risk of developing advanced adenoma or carcinoma, and for this reason referral for optical colonoscopy with polypectomy is advised. Patients with polyps larger than 1 cm should also be referred at once for colonoscopy and polypectomy/mucosectomy since 10%–25% of these lesions have high-grade dysplasia or carcinomatous components. Patients with colonic masses suggestive of malignancy should be referred to a surgical or oncology unit.
These are the basic principles by which intracolonic lesions are categorized and recommendations made for their management.
Categories and Practical Application of the C-RADS Classification for Colonic (C) Lesions
Colonic lesions are divided into five categories C0–C4 (Table 5.2).
C0 mainly includes studies that do not permit adequate diagnostic classification because of technical limitations (Fig. 5.2). Incomplete studies may be due to inadequate bowel preparation or suboptimal colon distension. At some centers the number of C0 studies is also considered a measure of quality management. Another reason for a C0 classification is not having access to the results of prior studies which are needed for a proper evaluation of findings. With PACS image archives, this generally only occurs if the prior study was performed elsewhere. Access to prior studies is clinically relevant for surveillance after a C2 examination to follow up one or two polyps measuring 6–9 mm or an indeterminate polypoid finding.
C1 refers to a “normal”-appearing colon with polypoid lesions 6 mm in size or greater result under adequate examination conditions. This category may also include the presence of diminutive polyps (5 mm or smaller), assuming there are no other colonic lesions that are in a higher category. Such tiny polyps are considered negligible. Other C1 findings include lipomas and nonneoplastic findings (Fig. 5.3). In the opinion of the authors, it is necessary to report the presence of larger lipomas and relevant nonneoplastic changes. The former may be symptomatic (see Chapter 4, “Lipomas,” p. 106) and the latter, for example postinflammatory changes, may also be clinically relevant.
C2 is for findings that are very unlikely to represent advanced adenoma. This typically includes the presence of only one or two intermediate polyps measuring 6–9 mm in diameter (Fig. 5.4). Carcinomatous components are very rare in polyps of this size and, even if present, would very likely still be in a relatively early stage after a 3-year interval. If, during CT colonography follow-up, there are signs of lesion growth, colonoscopic removal should be considered. Along with clearly identifiable polyps, C2 is also the category assigned when indeterminate polypoid lesions 6 mm in size or larger are found that cannot be confidently diagnosed in a technically adequate exam. Despite good examination conditions, the interpreter cannot be absolutely sure that the lesion is not a true polyp: The possibility that it is a true polyp cannot be entirely ruled out (Fig. 5.5). Due to the uncertainty of the findings, a shorter follow-up interval than the currently standard 5 years should be chosen.
C3 lesions are those with an increased risk for the presence of high-grade dysplasia or carcinomatous components. This category includes findings of one or more polyps larger than 1 cm and three or more polyps between 6 and 9 mm in size (Fig. 5.6). Because of the increased risk of development of advanced adenoma or malignant transformation, patients with such lesions should be referred for endoscopic resection of the lesion.
C4 lesions are those that are suggestive of malignancy. Such lesions include malignant-appearing colonic masses with a typical semicircumferential or circumferentially stenotic morphology. Further evaluation with regard to radiological TNM staging is often possible on 2D CT views. For C4 findings, surgical and/or oncological referral is indicated to decide on further management (Fig. 5.7).