The incidence rate of colon cancer detected by routine colonoscopy performed after conservative treatment of right colon acute uncomplicated diverticulitis was low at 0.3% (1/330 cases). The detection rate of adenoma in the whole colon was 20.9% and the frequency of advanced adenoma was 2.7%.
Clinically, the features of right colon diverticulitis are different from those of left colon diverticulitis. Specifically, compared to left colon diverticulitis, right colon diverticulitis tends to occur at a younger age, with a lower Hinchey stage, and a lower rate of recurrence (3.1% versus 17.9% for left colon diverticulitis) . Based on these facts, and considering the high diagnostic yield of CT imaging and the development of accurate pathological finding for colon cancer, the utility of routine colonoscopy in patients after treatment of acute right colon diverticulitis, in the absence of complications, such as perforation, abscess formation, and/or obstruction, has been questioned . It has also been questioned if the incidence of colorectal cancer at younger ages is indeed more common on the left than on the right colon .
Several studies have been published on the effects of routine colonoscopy after conservative treatment of acute uncomplicated diverticulitis. Among 205 patients who underwent colonoscopy or CT colonoscopy for all colonic diverticulitis, regardless of the colonic segment involved, Westwood et al. reported a detection rate of 9.3% for adenomas and 0.5% for colorectal cancer . Additionally, Horesh et al. reported a rate of malignant findings of 1.6%, among 310 patients, for all of those with colonic diverticulitis who underwent colonoscopy. Of specific clinical relevance is the finding that there was no incidence of adenocarcinoma of the colon on follow-up colonoscopy after uncomplicated colon diverticulitis among patients younger than 50 years of age . However, the majority of this evidence included only patients with left colon diverticulitis. In fact, to our knowledge, only two previous studies addressed right colon diverticulitis [15, 16] . In their study of 109 patients with right-sided colon diverticulitis, Hashimoto et al. did not identify any cases of colorectal cancer, with a rate of advanced adenoma of 6.4% (7/109 cases) and non-advanced adenoma of 21.1% (23/109 cases) . Chan et al. reported on 27 patients with right colon diverticulitis, with no incidence of colorectal cancer or advanced adenoma identified . However, both of these studies included a small number of patients. By contrast, our study included 330 patients, a relatively large sample size. Similar to previous findings, adenoma and cancer detection rates were very low. Of significance was our finding that adenoma were identified only in the right colon.
According to a previous population-based study evaluating the prevalence of colorectal adenomas in asymptomatic Korean men and women published in 2014 , the prevalences of colorectal adenomas and advanced adenomas were 34.5% and 3.1%, respectively. On subgroup analysis, in patients <50 years of age, the adenoma detection rate was 20.6-24.4%, which was comparable to the rate in our study (20.9%). However, the rate of advanced adenoma detection was fairly higher in our study (2.7%) than in this previously reported study (1.1-1.7%). This suggests that patients with right uncomplicated colonic diverticulitis are more likely to have advanced colon adenoma; therefore, routine colonoscopy should be performed for these patients.
The adenoma detection rate (ADR) has been associated with the interval risk of colorectal cancer . The ADR can be used as a colonoscopy quality indicator, with an ADR of <20% being associated with a 10-fold increase in the interval cancer risk . The ADR in our study, which included only patients with right colon diverticulitis, was 20.9%. We consider this rate to be appropriate for our study as our primary outcome was the detection rate of colon cancer.
A previous study reported that complicated diverticulitis is more likely to be associated with colon cancer compared to uncomplicated diverticulitis . Therefore, our study also included patients with complicated diverticulitis, with comparison between patients with complicated and uncomplicated diverticulitis. However, the number of patients with complicated diverticulitis in this study (n=47) was lower than that in the previous study (n=172). Of the 47 patients included in our study group, 8 underwent emergency surgery, and all patients were diagnosed with diverticulitis after surgery. In addition, only 21 of the 39 patients underwent routine colonoscopy, among whom no colon cancer was found (see Supplementary Tables). Therefore, we excluded patients with complicated diverticulitis.
The limitations of our study need to be acknowledged. Foremost, this is a retrospective study, with no knowledge of the outcomes of colonoscopy surveillance for patients who did not undergo follow-up colonoscopy. We do note that patients who did not undergo follow-up colonoscopy tended to be younger than those who did undergo colonoscopy follow-up, although there was no statistical significance. Furthermore, among the total of 355 patients (57.7%), including patients who performed follow-up colonoscopy at another hospital and those who underwent colon barium were confirmed that there was no colon cancer. This rate (57.7%) of colonoscopy surveillance is comparable to previously reported rate in review articles [20, 21]. Second, as our study is not a population based, our findings do not provide an estimate of colon cancer incidence in all patients with uncomplicated right colon diverticulitis. However, the strength of our study is the relatively large sample size which, in fact, is the largest study to date evaluating routine colonoscopy results among patients with right colon diverticulitis.
In conclusion, in patients with acute uncomplicated right colonic diverticulitis, routine colonoscopy after conservative treatment may be necessary because it is possible to detect advanced colon adenoma. Especially, for patients under the age of 45 years with a positive family history for colon disease and for those over the age of 45 years who have not undergone colonoscopy within the last 3 years, screening colonoscopy is strongly recommended, which is consistent with published guidelines . It will be necessary to confirm the results of our study by collecting a larger number of patients through a multicenter or population based study.