DISCUSSION
Increased glucose metabolism has been reported in colorectal cancer. In 1962, Macbeth and Bekesi (10) showed increased anaerobic glycolysis in vitro in surgically resected colon cancers. Later FDG PET studies, which were based on in vivo measurement of glucose metabolism, showed high FDG uptake in both primary (3,11-13) and recurrent colorectal cancers (1,2,4,14). Primary colorectal cancers as small as 1.4 cm (3) and 1.8 cm (13) were detected with PET.
To our knowledge, this study is the first to describe in detail high FDG uptake in adenomatous polyps of the colon. Histologically, there are several types of benign colonic polyps—for example, adenoma, hyperplastic polyp, juvenile polyp, and inflammatory polyp. Adenomas and hyperplastic polyps are the most prevalent, and only adenomas have the potential for malignant transformation (6). In a previous study, 35 hyperplastic polyps (size range, 3-38 mm) were all negative on FDG PET (3). It is noteworthy that adenomatous polyps, which have the potential for cancer, accumulate FDG, whereas hyperplastic polyps, which do not have the potential for cancer, do not accumulate FDG.
Bạn đang xem: 18F-FDG PET Detection of Colonic Adenomas
In our study, the larger adenomas could be detected by FDG PET, whereas the smaller ones could not. The spatial resolution (full width at half maximum) of our PET machine is 6.0 mm in the axial plane, and for lesions less than twice this length (i.e., <12 mm), FDG uptake is underestimated because of the partial-volume effect. We believe that this partial-volume effect affected the detectability of the small adenomatous polyps in our study.
Xem thêm : Aceite de Krill Antártico
It is accepted medical practice to remove colonic adenomas when they are detected, although there is no consensus regarding the minimum size of the adenoma that should be resected. The likelihood of malignant transformation increases with the increase in adenoma size (6). Our study revealed that adenomatous polyps ≥13 mm could be detected incidentally during FDG PET study; adenomatous polyps ≥13 mm are large enough and should be resected.
In our study, adenomas in the cecum, ascending colon, or descending colon were more likely to be visualized by PET than were adenomas in other parts of the large intestine. This finding can be explained by the fact that the cecum, ascending colon, and descending colon are fixed at the retroperitoneum; mobility is restricted. It is possible that mobility, including peristaltic movement of the colon, affects the visualization of adenomas with PET. Because the study was retrospective, we could not give anticholinergic drugs. Our result could also be explained by the fact that the larger adenomas in our study subjects were seen in the cecum, ascending colon, and descending colon than elsewhere. For example, 12 of 26 adenomas ≥11 mm (46%) were seen in 1 of these 3 sites, whereas only 8 of 33 adenomas of this size (24%) were seen in the transverse and sigmoid colon. Although the difference was not statistically significant (Fisher’s exact test, P = 0.068), the tendency was toward the presence of larger adenomas in these 3 sites.
As is shown in Table 3, 2 PET-positive and polypectomized adenomas, 11 and 18 mm, were identifiable on PET images 15 and 12 mo earlier, respectively. This finding raises the possibility that colonic adenomas can be detected with PET at a stage that is treatable by endoscopic polypectomy.
Xem thêm : ADMA/SDMA
Double-contrast barium enema and colonoscopy are the gold standards for diagnosis of colonic adenomas. Both examinations are sensitive and relatively inexpensive, although the rate of detection with barium enema is related to adenoma size (8). Compared with these examinations, PET is insensitive and relatively expensive. Therefore, PET cannot substitute for barium enema or colonoscopy, and PET is not reliable as a screening tool for small adenomas. The advantage of PET imaging is that it can survey the entire body noninvasively, including the colon and rectum, without bowel preparation. PET can be an option for patients for whom bowel preparation, barium enema study, or colonoscopy poses a formidable barrier. It is most important to recognize that colonic adenomas can be detected incidentally during FDG PET study; the incidence of colonic adenomas is not low.
The degree of FDG uptake may relate to the degree of dysplasia in the adenoma. However, we were unable to investigate this relationship. The criteria for dysplasia differ among pathologists, and our pathologic diagnoses depended on reports from each hospital’s pathologist; 1 particular pathologist could not review all specimens. In addition, we did not perform transmission scanning for attenuation correction, and thus we were unable to quantitatively evaluate local FDG uptake. Further study should be done to determine how the degree of FDG uptake relates to the degree of dysplasia.
The large intestine is a well-known site of physiologic FDG uptake (15,16), and intestinal FDG uptake poses a practical problem in the evaluation of PET images. Intestinal uptake can hinder detection of FDG uptake in the adenoma. It can also be the source of a false-positive result. In our study, the rate at which false-positive findings resulted from intestinal FDG uptake was 5.5% (6/110 subjects). Scans interpreted as positive were interpreted incorrectly in as many as 32% subjects (6/19). Our posit is that, in addition to the suggestion of colonic carcinoma, distinct focal FDG uptake along the large intestine suggests the presence of colonic adenoma and this finding calls for prompt colonic examination by barium enema study or colonoscopy.
Nguồn: https://buycookiesonline.eu
Danh mục: Info
