Lesion Size and Colonic Segment Location

The Boston Working Group previously published guidelines on the reporting of colonic lesion features (Table 12.1) and the classification of colonic findings for the purposes of suggested follow up (Table 12.2). Some of those parameters will be explained here as they impact the reporting of CTC data.

The matching of conventional colonoscopy (CC) and CTC for size and location is required in order to understand the diagnostic accuracy of the technique. Every effort should be made to measure accurately the size of each lesion detected. Ideally, during endoscopy use of a caliper tool is ideal. Normally only an estimate is made by comparing the polyp to the size of the open forceps. Measurement of polyps by comparison to open forceps requires that the forceps be held as closely as possible to the lesion, a point that should be emphasized as a quality control measure. Thus polyp size as reported by CC is usually at best an estimate. Lesion localization to a colonic segment is also a rough estimate by CC, because the endoscopist has little direct extralu-minal reference by which to correlate the position of the endoscope within the colon. Even with new methods, such as a magnetic device attached to the endoscope that indicates endoscope location on the patient's skin, CC may be subject to overestimation of distance of the lesion from the rectum due to stretching of the colon by the endoscope. Thus comparison for lesion location is best done by review of a recorded video of the endoscopy when available. The matching of lesions between CC and CTC should include lesion relationship to folds (on-a-fold vs in between folds) and lesion morphology (sessile, pedunculated, and flat). When multiple lesions are present, sequence of lesions can be helpful as well. Because video recording the entirety of each colo-noscopy exam is not always feasible, an alternative is for the endoscopist to acquire still snapshots of pertinent views of colon anatomy. These images can demonstrate colon pathology in relation to local normal anatomy and can be readily compared with the rendered endoluminal reconstructions that are available on all commercial CTC display stations. These matching techniques should substitute for a simple "segment" analysis of lesion location, and reporting investigators should clearly state what method they employed to compare size and position of polyps. Caution should be used before concluding that a lesion found by CTC - but not CC - is a false positive, even if video endoscopy is available for review. Pickhardt et al. have shown that some of these represent false negative exams by OC due to a polyp being hidden behind a fold (Pickhardt et al. 2004a).

Table 12.1. Feature descriptors of colonic lesions

Lesion size (mm) For lesions 6 mm or greater, single largest dimension of polyp head (excluding stalk if present) in either,

MPR, or 3D views. The type of view employed for measurement should be stated Morphology Sessile-broad based lesion the width of which is greater than the vertical height Pedunculated-polyp with stalk

Flat-vertical height less than 3 mm above the surrounding normal colonic mucosa Location Refer to named standardized colonic segmental divisions: rectum, sigmoid, descending, transverse, ascending, and cecum Attenuation Soft tissue density

Table 12.2. Classification of colonic findings and suggested follow-up

C0. Inadequate study/awaiting prior comparisons

C1. Normal colon or benign lesion; continue routine screeninga

C2. Indeterminate lesion; surveillance recommended, or endoscopyb C3. Polyp, possibly advanced adenoma; follow-up colonoscopy recommended C4. Colonic mass, likely malignant; surgical consultation recommended0

Inadequate prep: cannot exclude lesions >10 mm due to fluid/feces

Inadequate insufflation: one or more colonic segments collapsed on both views

Awaiting prior colon studies for comparison

No visible abnormalities of the colon

No polyp >6 mm

Lipoma or inverted diverticulum

Non-neoplastic findings, e.g. colonic diverticula

Findings indeterminate; cannot exclude polyps >6 mm Polyp >10 mm

Three or more polyps, each 6-9 mm

Lesion compromises bowel lumen; demonstrates extra colonic invasion a Every 5-10 years b Evidence suggests surveillance can be delayed at least three years, subject to individual patient circumstance c Communicate to referring physician as per accepted guidelines for communication, such as ACR Practice Guideline for Communication: Diagnostic Radiology. Subject to local practice, endoscopic biopsy may be indicated

We favor the use of a six segment scheme when reporting the colonic segment location of a polyp. We suggest avoiding "hepatic flexure" and "splenic flexure" as separate segments. While the point of the flexure however is usually well-defined as the radiologic splenic and hepatic flexure - the first sharp curve in the colon at its most cephalad point - there is no defining transition between the flexure and the adjacent ascending, transverse or descending colon for the endoscopist. We suggest use of rectum, sigmoid, descending, transverse, ascending and cecum to report lesion location. We recognize that the defining points of the sigmoid are a matter of judgment of the radiology investigator and can vary according to the anatomy of each patient.

There remain differing opinions as to the best way to measure lesions. In most cases, lesion size can be measured accurately on magnified 2D multiplanar images. A notable exception is lesions that are oval which may be more accurately measured on 3D endoluminal views. We propose that for standardization, the largest single dimension be reported for a given lesion (analogous to RISC criteria for solid tumors), on 2D for round lesions and on 2D or 3D for oval lesions. Placing electronic cursors on the edge of a polyp on the 3D view is subject to error in that placement just beyond the edge of the polyp may markedly overestimate polyp size if the cursor is really placed on a nearby or distant colonic surface. As a result, we urge caution when making size measurements primarily on 3D endoluminal reconstructions. Investigators may wish to confirm correct placement of 3D cursors in another view before recording a measurement. While ideally, the average of several lesion measurements should be reported, but we recognize that this may not be feasible in all cases due to time constraints. Lesion shape should be given, e.g. round or oval, although the largest dimension should be used for reporting size. For pedunculated lesions the stalk diameter and length should be estimated. The selection of a particular window and level will also affect the apparent size of a lesion. We prefer lung window settings. In any event, the setting used should be specified.

To promote further standardization of reporting, we suggest that investigators should report polyps based on the following standard size categories: under 5 mm, >5 to <10 mm and >10 mm. Since large masses have a different conspicuity and clinical significance compared to polyps, they should be reported separately. More detailed data by exact size threshold (e.g. 6 mm, 7 mm, 8 mm and 9 mm sizes) is desirable. There is mounting evidence that a 6 or 7 mm size cut off is optimal and that reporting smaller lesions will adversely impact exam specificity. Annular cancers and masses 4.0 cm or larger be reported and analyzed separately from polyps. The size distributions of reported polyps has been a particularly frustrating issue in attempting to summarize reports, as some have used 7 mm or 8 mm size groupings. In some publications it is unclear how diminutive polyps (less than 5 mm) have been categorized. The data are overwhelming that specificity of CTC drops to unacceptable levels if lesions <5 mm are reported. In addition, there is growing consensus that the clinical significance of these diminutive polyps is quite small. The conclusion concerning clinical significance is based on the extremely low prevalence of carcinoma to be found in resected specimens of this size, and the fact that a large percentage of these lesions are hyperplastic in histology, hence carrying no malignant potential. In non-research situations, the lesions size can be first estimated by comparison to a scale on the 2D images. If the lesions is clearly <5 mm, time can be saved by not trying to measure or problem-solve these potential polyps.

When comparing lesion size to biopsy or pathology specimens, the report should indicate if the specimen was fresh or fixed. In either case, the lesion size as reported by the pathologist is likely to be smaller than that observed by either radiologist or endoscopist due to the combination of lack of blood flow and consequence of the fixation process.

The histology of the polyp should be categorized as adenoma (tubular, villous or mixed), adenocarci-noma, hyperplastic or normal mucosa. Hyperplas-tic polyps (and mucosal tags) are not pre-malignant, and several authors have suggested that hyperplas-tic polyps may flatten and be less conspicuous in well-distended or over-distended colons. In the case of diminutive lesions or difficult resections, the endoscopist is not always able to retrieve sufficient material to provide pathologic diagnosis. However, when available, this data aids in our understanding the prevalence and clinical significance of lesions. In addition, the ability to correlate of diagnostic performance to histology will be an important aspect of the validation of CTC since only the adenomatous lesions are pre-malignant. Therefore we recommend reporting sensitivity data for adenomatous lesions separately and for all lesions separately.

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