New diagnostic technologies can visualize colon polyps, but not remove them. There is clear consensus that polyps 10 mm or larger need to be removed. There is still controversy surrounding the appropriate reporting and management of small 1 to 5 mm and 6 to 9 mm polyps. The author recommends that patients whose largest polyp is 6 mm or larger should be offered colonoscopy. If the largest polyp is less than 6 mm in size, and imaged with high reliability, the author recommends reporting the finding, and individualizing the decision to pursue colonoscopy versus repeat imaging.
The dilemma
Structural examinations of the colon have evolved over time. Until the 1960s, full colon visualization could only be achieved with barium enema. With the advent of colonoscopy, direct visualization with polyp detection and removal were possible. Since 2000, new diagnostic technologies have emerged that enable visualization, but not removal, of polyps. Capsule endoscopy is new, and still under development. This discussion focuses on detection by computed tomographic colonography (CTC) of diminutive (1–5 mm) and small (6–9 mm) polyps.
These technologies create a dilemma: if polyps are visualized, do they need to be reported and do they need to be removed? Although there is clear consensus that polyps 10 mm or larger need to be removed, there is still controversy surrounding the appropriate reporting and management of small 1- to 5-mm and 6- to 9-mm polyps.
Background
Likelihood of Detection of Diminutive and Small Polyps
CTC
From 2003 to 2007, CTC technology was evolving with the development of hardware (64-slice computed tomography [CT] scanners) and software for 2-dimensional and 3-dimensional imaging of the colon. A large multicenter study was published in 2008 using modern technology and fully trained radiologists, which compared CTC to optical colonoscopy. The investigators did not report findings less than 5 mm. Sensitivity for detection of polyps 6 to 9 mm in size was 65.3%. In a recent study that used advanced adenoma as the end point (defined as >20% villous or high-grade dysplasia), CTC sensitivity for advanced lesions 6 to 9 mm in size was 56.7%.
Most experts believe that CTC is not accurate for detection of 1- to 5-mm lesions. These lesions are often barely polypoid (resulting in false-negative examinations) or may be confused with residual stool (resulting in false-positive examinations). One large study reported that CTC detected only 50 of 654 (7.6%) 1- to 5-mm polyps. Therefore, most studies do not include diminutive polyps in their analysis.
Colonoscopy
Colonoscopy is the gold standard for detection of polyps in the colon, but it is far from perfect. In tandem colonoscopy studies, patients had a colonoscopy by one endoscopist who noted all polyps, and then a second endoscopist who removed all polyps. Although polyps 10 mm or larger were rarely missed, small polyps of less than 10 mm were commonly missed. Hixson and colleagues reported missing 14.7% of polyps under 10 mm; Rex and colleagues reported missing 27% of polyps 1 to 5 mm, and 13% of polyps 6 to 9 mm in size. These studies may underestimate the miss-rate because lesions missed by the first examiner could also be missed by the second.
With the advent of CTC, colonoscopy could be compared with another modality by using a method of segmental unblinding. CTC was performed, followed by colonoscopy. After each segment of colon was examined, the CTC results were revealed to the endoscopist. If a polyp was seen on CTC, but not colonoscopy, the segment was reexamined. If a polyp was then found on the second look, it was considered a missed lesion at colonoscopy. Using this methodology, polyps 10 mm or larger were missed in 2% to 12% of colonoscopies performed by expert endoscopists who knew that their performance was being assessed.
Likelihood that Diminutive and Small Polyps are Neoplastic or have Advanced Features
Only 35% to 50% of small (1–5 mm) polyps will be neoplastic; 60% to 70% of polyps 6–9 mm will be neoplastic ( Table 1 ). Among lesions that are adenomatous, several studies have analyzed polyps for advanced features, defined as villous histology, high-grade dysplasia, or cancer in screening cohorts. For adenomas 1 to 5 mm, advanced features were found in 2.7% to 3.4% of adenomas 1 to 5 mm in size, and in 8.2% to 9.7% of adenomas 6 to 9 mm in size.
| 1–5 mm (% Neoplastic) | 6–9 mm (% Neoplastic) | |
|---|---|---|
| Pickhardt et al | n = 966; 35.6% | n = 262; 60.7% |
| Johnson et al | n = 392; 62.8% (5–9 mm) | |
| Rockey et al | n = 158; 61.4% | |
| Lieberman et al | n = 3744; 50% | n = 1198; 67.7% |
In the analysis by Lieberman and colleagues, the rate of advanced histology based on largest polyp size was determined. This analysis included polyps that were nonneoplastic. In patients whose largest was polyp 1 to 5 mm, the rate of advanced histology was 1.7%; if the largest polyp was 6 to 9 mm, the rate of advanced histology was 6.6%. Advanced histology was found in 30.6% of polyps 10 mm or larger.
Would Histologic Features or the Number of Neoplastic Polyps Help Inform a Surveillance Strategy for Patients?
Surveillance guidelines recommend a 3-year surveillance interval if patients have polyps with advanced histology or have 3 or more adenomas of any size. These data are based on evidence that such patients have a higher risk of developing advanced neoplasia during a surveillance period. Lacking histology or an accurate recording of the number of polyps, it would be difficult to recommend an appropriate surveillance strategy.
Background
Likelihood of Detection of Diminutive and Small Polyps
CTC
From 2003 to 2007, CTC technology was evolving with the development of hardware (64-slice computed tomography [CT] scanners) and software for 2-dimensional and 3-dimensional imaging of the colon. A large multicenter study was published in 2008 using modern technology and fully trained radiologists, which compared CTC to optical colonoscopy. The investigators did not report findings less than 5 mm. Sensitivity for detection of polyps 6 to 9 mm in size was 65.3%. In a recent study that used advanced adenoma as the end point (defined as >20% villous or high-grade dysplasia), CTC sensitivity for advanced lesions 6 to 9 mm in size was 56.7%.
Most experts believe that CTC is not accurate for detection of 1- to 5-mm lesions. These lesions are often barely polypoid (resulting in false-negative examinations) or may be confused with residual stool (resulting in false-positive examinations). One large study reported that CTC detected only 50 of 654 (7.6%) 1- to 5-mm polyps. Therefore, most studies do not include diminutive polyps in their analysis.
Colonoscopy
Colonoscopy is the gold standard for detection of polyps in the colon, but it is far from perfect. In tandem colonoscopy studies, patients had a colonoscopy by one endoscopist who noted all polyps, and then a second endoscopist who removed all polyps. Although polyps 10 mm or larger were rarely missed, small polyps of less than 10 mm were commonly missed. Hixson and colleagues reported missing 14.7% of polyps under 10 mm; Rex and colleagues reported missing 27% of polyps 1 to 5 mm, and 13% of polyps 6 to 9 mm in size. These studies may underestimate the miss-rate because lesions missed by the first examiner could also be missed by the second.
With the advent of CTC, colonoscopy could be compared with another modality by using a method of segmental unblinding. CTC was performed, followed by colonoscopy. After each segment of colon was examined, the CTC results were revealed to the endoscopist. If a polyp was seen on CTC, but not colonoscopy, the segment was reexamined. If a polyp was then found on the second look, it was considered a missed lesion at colonoscopy. Using this methodology, polyps 10 mm or larger were missed in 2% to 12% of colonoscopies performed by expert endoscopists who knew that their performance was being assessed.
Likelihood that Diminutive and Small Polyps are Neoplastic or have Advanced Features
Only 35% to 50% of small (1–5 mm) polyps will be neoplastic; 60% to 70% of polyps 6–9 mm will be neoplastic ( Table 1 ). Among lesions that are adenomatous, several studies have analyzed polyps for advanced features, defined as villous histology, high-grade dysplasia, or cancer in screening cohorts. For adenomas 1 to 5 mm, advanced features were found in 2.7% to 3.4% of adenomas 1 to 5 mm in size, and in 8.2% to 9.7% of adenomas 6 to 9 mm in size.
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