Elsevier

Academic Radiology

Volume 17, Issue 6, June 2010, Pages 784-790
Academic Radiology

Original Investigation
Flat (Nonpolypoid) Colorectal Lesions Identified at CT Colonography in a U.S. Screening Population

https://doi.org/10.1016/j.acra.2010.01.010Get rights and content

Rationale and Objectives

The aim of this study was to investigate the clinical importance and height definition of flat (nonpolypoid) colorectal lesions detected on screening computed tomographic colonography (CTC).

Materials and Methods

Results from prospective screening CTC in 5107 consecutive asymptomatic adults (mean age, 56.9 years) at a single center were analyzed. All detected colorectal lesions ≥ 6 mm were prospectively categorized as polypoid or flat (nonpolypoid). The maximal height of all flat lesions was measured to assess the suggested 3-mm threshold definition.

Results

Of 954 polyps measuring ≥ 6 mm identified on screening CTC, 125 lesions (13.1%) in 106 adults were prospectively categorized as flat, with a mean size of 12.7 mm (range, 6–80 mm), including 73 lesions 6 to 9 mm, 42 lesions 10 to 29 mm, and 10 lesions ≥ 3 cm (carpet lesions). For polyps between 6 and 30 mm in size, flat lesions were less likely than polypoid lesions to be neoplastic (25.0% vs 60.3%, P < .001), histologically advanced (5.4% vs 12.1%, P = .07) or malignant (0% vs 0.5%, P = NS). Two of 10 carpet lesions (20%) were malignant, compared to 50% of polypoid masses ≥ 3 cm. Of nine flat lesions seen only on colonoscopy (false-negatives on CTC), two were neoplastic (tubular adenomas), and none was histologically advanced. For all flat lesions between 6 and 30 mm, the maximal height averaged 2.2 mm and was ≤3 mm in 86.1%, including 93.2% of small 6-mm to 9-mm flat lesions.

Conclusion

In a US screening population, flat colorectal lesions detected on CTC demonstrated less aggressive histologic features compared to polypoid lesions. Excluding carpet lesions, a maximal height of 3 mm appears to be a reasonable definition.

Section snippets

Materials and Methods

The data source for this study was derived from screening CTC at a single institution in 5107 consecutive asymptomatic adults (2783 women, 2324 men; mean age, 56.9 ± 7.2 years) over a 51-month period from April 2004 through June 2008. This study cohort consisted of generally healthy outpatient adults representing a typical US screening population. The specific protocol used for bowel preparation, colonic distention, multidetector CT scanning, and interpretation of CTC has been previously

Prevalence and Histologic Features of Polyps Detected on CTC

A total of 954 nondiminutive colorectal lesions were identified in 636 individuals, of which 125 lesions (13.1%) in 106 adults were prospectively categorized as flat and 829 were labeled as polypoid (sessile or pedunculated) or masslike. The mean size (ie, the maximum lesion diameter excluding any stalk) of nondiminutive flat lesions was 12.7 mm (rang, 6–80 mm; Figure 1, Figure 2, Figure 3). According to polyp size categories, 73 flat lesions were small (6–9 mm) and 52 were large (≥10 mm). Of

Discussion

Since the original description of flat adenomas by Muto et al (17) in 1985, the true prevalence and clinical significance of nonpolypoid colorectal lesions has been widely debated. In particular, the relevance of flat lesions for colorectal cancer screening in the United States has not been well established. Our findings confirm that even when more stringent morphologic criteria are applied, flat lesions (ie, superficially elevated) do exist in a typical US screening population. Although they

References (49)

  • P.J. Pickhardt et al.

    Screening for nonpolypoid colorectal neoplasms

    JAMA

    (2008)
  • Robbins J, Pickhardt PJ, Kim DH. Flat (nonpolypoid) lesions detected at CT colonography. Presented at: Annual meeting...
  • P.J. Pickhardt et al.

    Colorectal cancer screening with CT colonography: key concepts regarding polyp prevalence, size, histology, morphology, and natural history

    AJR Am J Roentgenol

    (2009)
  • J. Fidler et al.

    Flat polyps of the colon: accuracy of detection by CT colonography and histologic significance

    Abdom Imaging

    (2009)
  • S.H. Park et al.

    Flat colorectal neoplasms: definition, importance, and visualization on CT colonography

    AJR Am J Roentgenol

    (2007)
  • D.H. Kim et al.

    CT colonography versus colonoscopy for the detection of advanced neoplasia

    N Engl J Med

    (2007)
  • P.J. Pickhardt

    Screening CT colonography: how I do it

    AJR Am J Roentgenol

    (2007)
  • P.J. Pickhardt et al.

    Flat colorectal lesions in asymptomatic adults: implications for screening with CT virtual colonoscopy

    AJR Am J Roentgenol

    (2004)
  • S. Rubesin et al.

    Carpet lesions of the colon

    Radiographics

    (1985)
  • P.J. Pickhardt et al.

    Linear polyp measurement at CT colonography: in vitro and in vivo comparison of two-dimensional and three-dimensional displays

    Radiology

    (2005)
  • M.E. Zalis et al.

    CT colonography reporting and data system: a consensus proposal

    Radiology

    (2005)
  • P.J. Pickhardt et al.

    Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults

    N Engl J Med

    (2003)
  • T. Muto et al.

    Small flat adenoma of the large bowel with special reference to its clinicopathologic features

    Dis Colon Rect

    (1985)
  • S.H. Park et al.

    Sensitivity of CT colonography for nonpolypoid colorectal lesions interpreted by human readers and with computer-aided detection

    AJR Am J Roentgenol

    (2009)
  • Cited by (49)

    • Computed Tomography Colonography vs Colonoscopy for Colorectal Cancer Surveillance After Surgery

      2018, Gastroenterology
      Citation Excerpt :

      The performance characteristics we report for CTC in the surveillance setting are somewhat lower than those in the screening setting, although the results are more comparable for polyps ≥10 mm. The inability of CTC to identify flat polyps is a potential concern in both screening and surveillance settings.23,24 Our study, in contrast to some recent reports,16 did not identify a significant difference in detection rates for serrated vs non-serrated polyps.

    • Imaging and Screening for Colorectal Cancer with CT Colonography

      2017, Radiologic Clinics of North America
      Citation Excerpt :

      The dual contrast tagging regimen likely improves the accuracy of CTC in several ways: (1) it increases specificity by tagging residual stool (barium effect) and decreases the amount of adherent stool (iohexol effect), (2) it increases sensitivity by allowing for detection in polyps submerged under fluid (iohexol effect), and (3) it improves detection of serrated and other flat lesions via surface coating of adherent contrast.26–29 This focal contrast coating can serve as a vital beacon for detection for flat lesions that may otherwise be relatively inconspicuous against the adjacent bowel mucosa (Fig. 1) and is also seen frequently in tubulovillous adenomas and other advanced neoplasms (Fig. 2).30–32 Once considered optional, these advantages demonstrate why the use of oral contrast tagging is now considered standard practice for CTC.

    • Current Issues in Computed Tomography Colonography

      2016, Seminars in Ultrasound, CT and MRI
    View all citing articles on Scopus
    View full text