Significance of Missed Polyps at CT Colonography
Significance of Missed Polyps at CT Colonography
Objective: Our purpose was to determine the clinical significance of polyps missed on CT colonography using histologic analysis and the natural history of colorectal polyps and to propose guidelines for follow-up colon surveillance based on CT colonographic findings.
Subjects and Methods: One hundred eighty-six men (age range, 40-87 years; mean, 62.3 years) underwent CT colonography immediately before conventional colonoscopy. All polyps detected on CT colonography were measured and imaged, and their segmental location was documented. All polyps detected on colonoscopy were measured, photographed, biopsied, and histologically analyzed. Results of CT colonography and conventional colonoscopy were compared with the final pathology reports. Conventional colonoscopy was used as the gold standard unless CT colonography showed a lesion measuring 10 mm or more that was not detected on conventional colonoscopy and had characteristics of a polyp. In these cases, follow-up conventional colonoscopy was offered.
Results: One hundred ninety-one polyps were detected on conventional colonoscopy. CT colonography prospectively detected 53 polyps. Histologic analysis of the polyps not detected on CT colonography showed that of those 5 mm or smaller, 58.1% were not adenomas, and of those measuring 6-9 mm, 42.8% were not adenomas. Both missed polyps at CT colonography of 10 mm or more were adenomas. Of the 22 polyps measuring 10 mm or more, three were not detected on conventional colonoscopy. Of these three, CT colonography showed a lesion having characteristics of a polyp, follow-up endoscopy confirmed the presence of the lesion, and histologic analysis showed a villous adenoma, a tubulovillous adenoma, and a tubular adenoma.
Conclusion: If CT colonography shows no abnormality, follow-up screening in 5 years is recommended. If CT colonography detects a lesion smaller than 5 mm, follow-up imaging in 3-5 years is recommended. If CT colonography detects a lesion measuring 6 mm or more, endoscopy and polypectomy should be offered unless contraindicated.
CT colonography is a relatively new noninvasive imaging technique that allows detection of colorectal polyps and cancers. The sensitivity of CT colonography for colorectal polyp detection is directly related to polyp size. Sensitivity for the detection of diminutive polyps (≤ 5 mm) is 10-67%. The sensitivity of the examination for larger raised polyps10 mm or moreis approximately 75-90%. Currently, the American Gastroenterological Association (AGA) states that CT colonography is a promising technique for colorectal screening but not yet ready for "prime-time" screening. A major concern is that CT colonography performs poorly for detecting small polyps.
However, many small colonic protrusions are normal colonic mucosa or hyperplastic polyps at pathologic evaluation. These lesions have no clinical potential to become carcinoma. Although small adenomas are not uncommon, their clinical significance has been questioned. One study found that of 357 adenomas smaller than 10 mm, only 11 showed severe dysplasia, and in only two was carcinoma found. In neither case was the lesion smaller than 5 mm.
Although it is generally agreed that most colorectal carcinomas develop from precursor adenomatous polyps, the dwell time and growth rate for these small polyps to become carcinoma is very long, estimated to be greater than 10 years. If colorectal screening is performed at routine intervals, detecting growth in these lesions should be possible.
The purpose of this study was twofold: first, to determine the histology and clinical significance of small polyps missed at CT colonography when compared with colonoscopy; and second, to propose an algorithm for follow-up screening, surveillance, and intervention based on various findings at CT colonography.
Objective: Our purpose was to determine the clinical significance of polyps missed on CT colonography using histologic analysis and the natural history of colorectal polyps and to propose guidelines for follow-up colon surveillance based on CT colonographic findings.
Subjects and Methods: One hundred eighty-six men (age range, 40-87 years; mean, 62.3 years) underwent CT colonography immediately before conventional colonoscopy. All polyps detected on CT colonography were measured and imaged, and their segmental location was documented. All polyps detected on colonoscopy were measured, photographed, biopsied, and histologically analyzed. Results of CT colonography and conventional colonoscopy were compared with the final pathology reports. Conventional colonoscopy was used as the gold standard unless CT colonography showed a lesion measuring 10 mm or more that was not detected on conventional colonoscopy and had characteristics of a polyp. In these cases, follow-up conventional colonoscopy was offered.
Results: One hundred ninety-one polyps were detected on conventional colonoscopy. CT colonography prospectively detected 53 polyps. Histologic analysis of the polyps not detected on CT colonography showed that of those 5 mm or smaller, 58.1% were not adenomas, and of those measuring 6-9 mm, 42.8% were not adenomas. Both missed polyps at CT colonography of 10 mm or more were adenomas. Of the 22 polyps measuring 10 mm or more, three were not detected on conventional colonoscopy. Of these three, CT colonography showed a lesion having characteristics of a polyp, follow-up endoscopy confirmed the presence of the lesion, and histologic analysis showed a villous adenoma, a tubulovillous adenoma, and a tubular adenoma.
Conclusion: If CT colonography shows no abnormality, follow-up screening in 5 years is recommended. If CT colonography detects a lesion smaller than 5 mm, follow-up imaging in 3-5 years is recommended. If CT colonography detects a lesion measuring 6 mm or more, endoscopy and polypectomy should be offered unless contraindicated.
CT colonography is a relatively new noninvasive imaging technique that allows detection of colorectal polyps and cancers. The sensitivity of CT colonography for colorectal polyp detection is directly related to polyp size. Sensitivity for the detection of diminutive polyps (≤ 5 mm) is 10-67%. The sensitivity of the examination for larger raised polyps10 mm or moreis approximately 75-90%. Currently, the American Gastroenterological Association (AGA) states that CT colonography is a promising technique for colorectal screening but not yet ready for "prime-time" screening. A major concern is that CT colonography performs poorly for detecting small polyps.
However, many small colonic protrusions are normal colonic mucosa or hyperplastic polyps at pathologic evaluation. These lesions have no clinical potential to become carcinoma. Although small adenomas are not uncommon, their clinical significance has been questioned. One study found that of 357 adenomas smaller than 10 mm, only 11 showed severe dysplasia, and in only two was carcinoma found. In neither case was the lesion smaller than 5 mm.
Although it is generally agreed that most colorectal carcinomas develop from precursor adenomatous polyps, the dwell time and growth rate for these small polyps to become carcinoma is very long, estimated to be greater than 10 years. If colorectal screening is performed at routine intervals, detecting growth in these lesions should be possible.
The purpose of this study was twofold: first, to determine the histology and clinical significance of small polyps missed at CT colonography when compared with colonoscopy; and second, to propose an algorithm for follow-up screening, surveillance, and intervention based on various findings at CT colonography.
