Worldwide, colorectal cancer (CRC) is the third leading cause of cancer death . It is the third most common cancer in the United States, and African-Americans have the highest incidence rate of CRC among the different races . Previous reports suggest a low incidence of CRC in Africa but recent evidence from most sub-Saharan African countries has shown a sharp rise in the incidence of CRC [2,3]. Plausible reasons for this rise include the adoption of westernized diet, greater awareness of CRC, improved diagnostic services and better-functioning cancer registries. A polyp is defined as any mass protruding into the lumen of a hollow viscus . Colorectal polyps may be classified by their macroscopic appearance as sessile (flat, arising directly from the mucosal layer) or pedunculated (extending from the mucosa through a fibrovascular stalk) . Colorectal polyps may also be histologically classified as neoplastic or as non-neoplastic (hyperplastic, hamartomatous, or inflammatory). Neoplastic (adenomatous) colorectal polyps are benign tumors that originate from the mucus-secreting colonic epithelial cells . The significance of colorectal polyps, especially the adenomatous polyps, comes from the fact that they are generally accepted to be precursors to CRC. Colon carcinogenesis takes several years through a multistep pathway that includes initial hyperproliferation of normal epithelial cells to formation of adenomas and finally the transition to invasive carcinomas . It is well-known that colonoscopy is considered the gold standard for the detection and prevention of CRC . Among the various diagnostic tools available, colonoscopy enables clinicians to simultaneously screen and prevent CRC by removing cancer predisposing polyps such as adenomatous polyps and serrated polyps, leading to reduction in the incidence and mortality from CRC observed in patients with previous polypectomy . Interruption of adenoma-carcinoma sequence with colonoscopy and polypectomy reduces the incidence of CRC by as much as 90% .
The reported prevalence of colonic polyps varies widely between different geographical areas. It was estimated that 30% of the Western population have colonic polyps, whereas lower rates (10–15%) were noted in Africa [8,9]. Recent studies in Nigeria and other sub-Saharan African countries have reported different prevalence rates of colonic polyps that appear to suggest that their occurrence in these countries may not be rare as previously noted [10–17]. Results from previous studies have also shown that colonic polyps are more common in men than in women and increase in frequency with increasing age in most of these studies.
Although reports are scanty from sub-Saharan Africa in general, recent studies note rising incidence of CRC and prevalence rates of colonic polyps among Africans. In Nigeria, most of the available scanty reports are from the southern region, reports are rare from the northern region. Accruing data about the prevalence of colonic polyps may help direct public health policies and resource allocation for prevention of CRC. This study, therefore, aimed to determine the prevalence, distribution and histopathological characteristic of colonic polyps among Nigerians who underwent colonoscopy at a tertiary health facility in North-central Nigeria.
2. Materials and Methods
Study design: This was a hospital-based retrospective study.
Study methods: A retrospective analysis of prospectively collected data was performed using clinical information from the endoscopy logs and pathology database system of University of Ilorin Teaching Hospital, Ilorin, Nigeria. All consecutive patients who had polyps diagnosed at colonoscopy over a 4 year and half year period (March 2013–September 2017) were included. The study cohort comprised patients who were referred from the Medical, Surgical, and General Out-patient Clinics of the hospital, surrounding secondary and private health facilities in the state as well as patients referred from neighboring states. Patients who had incomplete procedure due to any cause were excluded from the cohort. The research was approved by the Ethics and Research Committee of the University of Ilorin Teaching Hospital. Informed consent was obtained from all patients prior to the procedure. Analgesia was provided to all the patients by giving intravenous tramadol 100mg and conscious sedation was given when required by using intravenous midazolam (mean dose 2.5 mg). The colonoscopies were performed using an Olympus CF-180 Evis Exera II colonoscope. All polyps identified during colonoscopy were either biopsied or removed endoscopically and submitted for histopathology. The location of the polyp(s) was defined as recto-sigmoid (rectum and sigmoid colon) and proximal colon (from caecum to descending colon) on the assumption that sigmoidoscopy usually does not reach beyond the sigmoid-descending colon junction . The number of polyps – whether the polyps were single or multiple – was noted; the gross appearance of the polyp was classified as either sessile or pedunculated.
Definition of terms: Polyp detection rate (PDR) was defined as the number of colonoscopies in which one or more polyps were detected, biopsied, and sent for histology, divided by the total number of colonoscopies that was carried out. Adenoma detection rate (ADR) as defined as the number of polyps that were histologically diagnosed as adenomatous taken as a proportion of the total number of colonoscopies.
3. Statistical Analysis
Data analyzed include patients' biodata, indications for colonoscopy, colonoscopic findings, presence of polyps, histopathological characteristics of the polyps as well as the PDR and ADR. Patients were stratified by age into two groups (Age 50 and 50 years). Categorical variables were expressed as numbers and percentages. Chi-square or Fisher's exact test, where appropriate, was used for the analysis of categorical variables. Continuous variables were expressed as means and standard deviation or medians, as appropriate. All analyses were performed using SPSS version 17.0 (SPSS INC, Chicago, IL, USA). A two-tailed P 0.05 was considered as statistically significant.
Over the study period, 289 patients met the inclusion criteria for the study. There were 178 males (61.6%); giving a male to female ratio of 1.6:1. Their ages ranged from 14 to 90 years (mean = 57.3 years) with the highest frequency of 69 (23.9%) observed in the 61–70 years age group (Table 1). There was no statistically significant difference in the ages of both sexes. Only 50 patients had colonic polyps. The overall PDR in the study group was 17.3%. Thirty-seven (74.0%) patients were above 50 years (p = 0.16). There were 33 (66.0%) males and 17 (34.0%) females with colonic polyps in the study population (p = 0.481). Eight (16.0%) of the patients with colonic polyps had co-existing colorectal mass at colonoscopy (p = 0.638). Twenty-seven (54.0%) patients were referred as a result of hematochezia, 7 (14.0%) for suspicion of CRC, 4 (8.0%) for abdominal pain, and 3 (6.0%) for routine screening. Other referral diagnosis included chronic diarrhea, constipation, and change in bowel habit. There was no statistical difference in the referral diagnoses of patients (p = 0.588).
|Age group (years)|
Twenty-three patients (46.0%) had polyps located proximal to the sigmoid colon, whereas 22 (44.0%) had polyps located at the recto-sigmoid region of the colon. Five (10.0%) patients had multiple polyps involving both segments. Twelve (24.0%) patients had pedunculated morphology, 36 (72.0%) had sessile morphology, whereas 2 (4.0%) had a combination of the two morphologies. The endoscopic images of two of the morphologic types found among the study cohort are shown in Figures 1(a) and (b). More than half of the polyps located in the recto-sigmoid region of the colon (63.6%) were found in the rectum. Twenty seven polyps were located proximal to the sigmoid colon in patients above 50 years compared to 5 polyps in those aged 50 years or younger (p = 0.099). The histopathology results of 39 patients were available for analysis, whereas other results were missing. Fourteen (35.9%) of these had adenomatous polyps; 12 (30.8%) patients each had inflammatory polyps and hyperplastic polyps; 1 (2.6%) had malignant polyp. The ADR for our cohort was 4.8. Of the patients with adenomatous polyps, two patients had Familial adenomatous polyposis (FAP) as they had more than 100 adenomatous polyps though genetic study was not conducted (see Figure 1(c)). Their ages were 45 and 49 years. Both patients had co-existing colonic cancer; one had surgery followed by chemotherapy, whereas the other was lost to follow-up. Seven (58.3%) of the remaining 12 patients with adenomatous polyps had tubular adenomas, 4 patients (33.3%) had tubulovillous adenoma, and 1 (8.4%) patient had Peutz-Jegher's polyp with adenomatous change (see Figures 2(a) and (b)).
The prevalence of colorectal polyps varies widely among different populations. Colorectal polyps are believed to be rare among black Africans . Recent data from Nigeria and other sub-Saharan African countries suggest that they may not be as rare as previously reported though the prevalence rates are still relatively low when compared to the rates reported among Caucasians and Asians [10–17]. Over a period of 4 years, a total of 50 of the 289 patients who underwent colonoscopy in our center had colorectal polyps giving a prevalence rate of 17.3%. This PDR of 17.3% is similar to the 15.5% earlier obtained by Olokoba et al. in a hospital-based cross-sectional study of the indications and findings at colonoscopy carried out at the Endoscopy unit of Crescent hospital, a privately owned specialist hospital in Ilorin, from January 2010 to May, 2012 . It is, however, higher than the PDR of 10.2% obtained in Jos, Plateau State, which is also located in the North Central region of Nigeria . The observed difference may be due to the fact that on average the patients in the Jos study were more than a decade younger than the participants in our study and the smaller size of their study population. Our observed prevalence rate is similar to the rate of 16.2% obtained by Alatise et al. in Ile-Ife, South Western, Nigeria . In Ado-Ekiti, South-western region of Nigeria, the prevalence of polyps was 14.7% among patients with lower GI bleeding. The differences in the patient selection, geographical location, and sample size (289 versus 68) may account for the difference in the observed prevalence rate . Oluyemi et al. and Onyekwere et al. in Lagos, South-western Nigeria obtained PDR of 11.2% and 6.8%, respectively [10,13]. A PDR of 1.0% was obtained by Obonna et al. in Ondo, South-western Nigeria . It is, however, lower than the rate of 20.8% obtained in Saudi Arabia . The PDR in East Azerbaijan, Iran, was 14.4% . An overall PDR of 23.5% and 42.0% was observed in two other studies from Iran [22,23]. These prevalence rates from Africa and the Middle East are much lower than the rates reported in Europe and the United States. Some of the reported PDR from the latter include 35.5%, 45.8%, and 49.0% from France, Spain, and the United States, respectively [24–26]. Our ADR of 4.8% is the same as that obtained in Lagos, lower than the 6.8% obtained in Ile-Ife but higher than 2.9% obtained in Ghana [10,11,17]. These ADRs from African countries are, however, much lower than the 17.7%, 19.4%, and 31.0% obtained in France, Germany, and the United States, respectively [24,26,27]. Several factors have been identified to influence PDR and ADR. These include personal or family history of polyps and/or CRC, the use of split-dose bowel preparation, documentation of withdrawal time, and overall procedure time, patients' gender and age (over 50), alcohol and cigarette-smoking history, issuance of annual performance report cards especially among physicians with low ADR 25%, the level of Endoscopist's experience and expertise, differences in exclusion criteria, the quality of the endoscopic devices, and the time of the day that the procedure was done [28–34]. This study also showed that close to half of the polyps (46.0%) were found proximal to the sigmoid colon. The implication of this is that perhaps almost 50% of the polyps may be missed if flexible sigmoidoscopy is used to evaluate patients in our environment. This is more than the 33.3%, 22.2%, and 38.0% that was reported in Ile-Ife, Lagos, and the United States [10,11,35]. Colonoscopy rather than sigmoidoscopy may thus be a preferred screening tool in our environment. In this study, we found more polyps in patients older than 50 years compared to those aged 50 years or younger but the difference was not statistically significant. In addition, more right-sided polyps were recorded in the patients above 50 years of age. This study did not find any association between age and the location of polyps that is similar to the finding in Ile-Ife but contrast with a previous study that showed that incidence of right sided polyps increased with increasing age [11,36]. In concordance with previous studies, we found that more males had polyps than females. Though the reasons for low polyp rate in women are not known, factors such as the protective role of oestrogen, decreased secondary bile acid production, and decreased serum levels of insulin-like growth factors in women have been suggested as plausible reasons [37–40]. We did not find any statistical relationship between sex and location of the polyps. The commonest indication for colonoscopy among the patients with polyps was hematochezia, a similar finding to previous studies [10,11,41]. It, however, contrasts with the finding of abdominal pain as the commonest presentation in Iran .
A limitation of this study is that some of the data on histology of colonic polyps were missing thus the ADR may be higher than the 4.8 recorded in this study. In conclusion, we found that the PDR of 17.3% from our facility is consistent with the estimated polyp prevalence of 10.0–15.0% in Africa. Near half of the polyps were located proximal to the sigmoid colon with the implication that these would have been missed if flexible sigmoidoscopy alone was employed in evaluating our patients. Males and older ages may benefit more from colonoscopy in our population.
• Study concept and design: Dr. M. O. Bojuwoye
• Collection of data: Dr. M. O. Bojuwoye, Dr. A. A. Adeyeye, Dr. O. O. K. Ibrahim, Dr. K. C. Okonkwo, Dr. A. M. Aliyu
• Analysis and interpretation of data: Dr. M. O. Bojuwoye, Dr. S. O. Agodirin, Dr. J. A. Ogunmodede, Dr. A. B. Olokoba and Dr. O. A. Ogunlaja
• Draft and revision: Dr. M. O. Bojuwoye, Dr. A. B. Olokoba, Dr. O. A. Ogunlaja, Dr. S. O. Agodirin, Dr. O. O. K. Ibrahim.
• Final approval of manuscript by all the authors.