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Table of Contents
Year : 2022  |  Volume : 14  |  Issue : 1  |  Page : 11-23

Colonoscopy practice and polyp detection in Nigeria: A systematic review

1 Department of Surgery, University of Port Harcourt, Choba, Rivers State, Nigeria
2 Department of Surgery, PAMO University Port Harcourt, Rivers State, Nigeria
3 Department of Internal Medicine, Federal Medical Centre Yenagoa, Bayelsa State, Nigeria

Date of Submission13-May-2022
Date of Acceptance13-Jun-2022
Date of Web Publication21-Jul-2022

Correspondence Address:
Emeka Ray-Offor
Department of Surgery, Faculty of Clinical Sciences, University of Port Harcourt, Choba, Rivers State
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njgh.njgh_8_22

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Evaluation of colorectal pathologies by colonoscopy is increasingly reported from different centers across Nigeria. However, a comprehensive review of current colonoscopy practice across the country is yet to be documented. To report on colonoscopy practice, the detection rate, site(s), and geographic distribution of colorectal polyps in Nigeria, a systematic search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The search databases comprised MEDLINE, African Journal Online, and Google Scholar. The eligibility criteria included publications on flexible lower gastrointestinal endoscopies (LGIEs) performed on Nigerian population over a 20-year period from January 2002 to 2022. Relevant data on study characteristics, demographics of study patients, indication(s), complications of polypectomy, quality metrics for colonoscopy, polyp morphology size, location, and histopathology were extracted and analyzed. Twenty-one observational studies were included comprising 5821 patients who underwent LGIE with an age range of 2–101 years and an M: F of 1.8:1. The polyp detection rate (PDR) was 8.5% in North-West Nigeria, and the mean value ranged from 11.3% [95% confidence interval (CI) 7.0–15.6] in South-West Nigeria to 38.0% (95% CI 165.3–241.3) in South-South Nigeria. The rectosigmoid segment had the highest frequency of polyps [43% (358/828)], and adenomatous, inflammatory, hyperplastic, and malignant polyps were the frequent histology reported: 221 (26.7%), 174 (21.0%), 38 (4.6%), and 13(1.6%), respectively. Summarily, a large disparity exists in PDR among endoscopists in Nigeria. The training of Nigerian endoscopists on techniques to enhance caecal intubation rate, polyp detection, and comprehensive documentation of quality metrics in colonoscopy studies are recommended.

Keywords: Colon and rectum, colonoscopy, Nigeria, polyps

How to cite this article:
Ray-Offor E, Ijah RO, Egboh SMC. Colonoscopy practice and polyp detection in Nigeria: A systematic review. Niger J Gastroenterol Hepatol 2022;14:11-23

How to cite this URL:
Ray-Offor E, Ijah RO, Egboh SMC. Colonoscopy practice and polyp detection in Nigeria: A systematic review. Niger J Gastroenterol Hepatol [serial online] 2022 [cited 2023 Mar 21];14:11-23. Available from: https://www.njghonweb.org/text.asp?2022/14/1/11/351556

  Introduction Top

Colorectal cancer (CRC) burden is increasing in many countries around the world. Global incidence estimates report CRC as the third most common cancer next to breast and lung cancers.[1] The progression of benign neoplastic polyps (adenomas) of the colon and rectum to a malignant state is an established pathway in the origin of CRC.[2] Multiple factors are responsible for the presence and development of CRC including population characteristics, living habits, and health conditions.[3] A rapid economic growth with westernization of diet and lifestyle is posited as reasons for the rapid rise in the incidence of CRC in sub-Saharan Africa.[4] There is increasing availability of modern diagnostic radiologic and endoscopic facilities with an increased detection rate of CRC in Nigeria.

Modern minimally invasive fiberoptic techniques of endoscopy are invaluable in the detection and removal of colorectal polyps. It is reported that the screening of the colon and rectum by colonoscopy and sigmoidoscopy is associated with significant CRC mortality reduction: 74% [odds ratio (OR) 0.26, 95% confidence interval (CI) 0.23–0.30] and 35% (OR 0.65, 95% CI 0.48–0.89), respectively.[5] However, the latter is not associated with any reduction in proximal CRC mortality.[5] The practice of colonoscopy in Nigeria is increasingly reported from different institutions and localities within the country.[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26] However, a comprehensive review of colorectal polyp prevalence across Nigeria is yet to be documented.


The study aimed to report on colonoscopy practice, the detection rate, site(s) and geographic distribution, and histopathology of colorectal polyps in Nigeria.

  Materials and methods Top

This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.[27] No ethical approval was required for this study.

Eligibility criteria

The eligibility criteria included publications on flexible lower gastrointestinal endoscopies (LGIEs) performed on symptomatic and asymptomatic Nigerian population from January 2002 to 2022 (20 years). Only literature documented in English language was included. The following were excluded for consideration: case reports, conference abstract presentations, dissertations, and systematic reviews. In addition, literature on flexible LGIEs with non-inclusion of data on colorectal polyps was excluded.

Information source

A careful search was performed on MEDLINE, African Journal Online (AJOL), and Google Scholar. Additional relevant cross-referenced literatures were searched, and correspondence phone calls made to authors for the full text of publication where this was not available online or if clarifications were needed.

Search strategy and screening

A systematic search was conducted on the aforementioned search engines. For MEDLINE, an advanced search was conducted with the following terms applied: Colonoscopy OR colonoscop* OR ileoconoscop* OR Sigmoidoscopy OR Sigmoidosc* OR Flexi-Sigmoidosc* OR lower gastrointestinal endoscopy OR colonosc* NOT proctoscopy AND Polyp OR polyps OR mucosal lesions OR neoplasm OR mucosal growth OR adenoma OR benign OR malignant OR serrated OR sessile OR pedunculated OR flat OR excavated AND Nigeria OR sub-Saharan Africa OR black Africa. The filters used were “Abstracts,” “free full text,” “full text,” and “Review” in the last 10 years. On AJOL, search was conducted using the search terms: colon, rectum, polyp. For Google scholar, the search terms used were: (polyp* colon* sigmoid* rectal* colorectal* large bowel* colonoscopy* diagnostic colonoscopy* therapeutic colonoscopy* Nigeria#). Individual search was conducted by clinical investigators (ER-O, RFOAI, S-MCE) with a consensus agreement during virtual meetings among all 3 authors on the publications for eligibility criteria after screening of title, abstracts, and, in some cases, the full text.

Data extraction

The data extracted included: author(s)’ names; period of study; years of study; study design; population and setting; demographics of patients; and indications for colonoscopy. Also extracted were site of polyps and quality indices of colonoscopy including polyp/adenoma detection rate (ADR), complications of polypectomy, sedation/analgesia protocol, and cecal intubation rate with diagnostic yield.

Risk of bias

The risk of bias assessment of the quality of individual studies was done using the approach outlined by the Strengthening the Reporting of Observational Studies in Epidemiology checklist.[28] This comprises a 22-item checklist for the following sections of articles: Title and abstract (item 1), Introduction (items 2 and 3), Methods (items 4–12), Results (items 13–17), Discussion (items 18–21), and other information (item 22) on funding. Three reviewers independently appraised the methodological quality and assigned score to each item; “0,” “1,” or a maximum score of “2,” depending on how they meet the requirements of each item. By assigning one score to each item, papers could get a total minimum score of 22 and a maximum score of 44. These ratings are provided in a table [Supplementary Table 1]. Articles that scored 22 points and above were included in our review.
Supplementary Table 1: Risk of bias assessment of studies using Strengthening the Reporting of Observational Studies in Epidemiology checklist

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Summary measures

Summary sheets were collated on Microsoft Word in tables for study profiles, demographics and indications for colonoscopy, quality indicators of colonoscopy, polyp sites, size, and histopathology and analyzed for frequency. Descriptive statistical analyses were computed for continuous variables, including means, standard deviations (SDs), minimum and maximum values, as well as 95% CIs. For categorical variables, frequencies were used.

Definition of terms

Polyp detection rate (PDR)

The proportion of patients from the total study population undergoing colonoscopy with at least one polyp detected.

Polyps per case (PPC)

The proportion of all polyps detected in the total study population.

Adenoma detection rate (ADR)

The proportion of patients from the total study population undergoing colonoscopy with at least one adenoma detected.

Cecal intubation rate (CIR)

The proportion of patients in whom the endoscopist was able to navigate endoscope up to the cecum as confirmed by visualization of triradiate fold, appendiceal orifice, or intubation of the ileo-cecal valve.

Diagnostic yield:

The proportion of patients in the study population with a positive diagnosis during investigation.

Additional analysis

A regional comparison of diagnostic yield rate, PDR, ADR, and CIR was done with analysis of variance. Statistical significance was set at < 0.05. The statistical software used was IBM SPSS Statistics (version 20; IBM Corporation, Armonk, NY, USA).

  Results Top

Study characteristics

Twenty-one publications were included in this review. A flow diagram shows the search strategy, screening, and study selection method [Figure 1]. These were all observational studies and predominantly conducted in public hospitals of Nigeria [Table 1]. No randomized controlled study involving polyp detection was identified in the literature search. A geographic sub-categorization of study settings in the publications showed 11 were conducted in South-West, 5 in North-Central, 2 in South-East, 2 in South-South, and one in North-West Nigeria.
Figure 1: Flow diagram

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Table 1: Profile of studies

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A total of 5821 patients underwent flexible LGIEs: 43 sigmoidoscopies and 5778 colonoscopies. The ages of patients ranged from 2 to 101 years and comprised 3381 (58.1%) males and 1851 (31.8%) females; data were missing for 589 (10.1%) patients. For cases of polyps, a total of 828 patients had at least a polyp detected during the colonoscopy procedure; however, only seven studies had details of demographics of patients with polyps detected. In these studies, an age range of 2–88 years (mean 57.3) was reported, and 64.2–88.8% of these patients with polyps were aged >50 years [Table 2]. A summary of gender distribution in these reported cases showed 263 males and 147 females (M: F=1.8:1) [Table 3].
Table 2: Demographics of total study population

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Table 3: Demographics of study population with polyps detected

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Indications for colonoscopy

The seven most common indications for colonoscopy among study patients in decreasing order of frequency were: gastrointestinal bleeding 2760 (52.5%); change in bowel habit 1148 (21.8%); abdominal pain 733 (13.9%); suspicion of CRC 321 (6.1%); unexplained anemia 273(5.2%); screening for CRC 252 (4.8%); and unexplained weight loss 228 (4.3%) [Table 4].
Table 4: Indications for colonoscopy

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Quality metrics of colonoscopy

Only five studies documented the sedation analgesia protocol: conscious sedation using benzodiazepine (midazolam or diazepam) and an opioid analgesic (pethidine or pentazocine) in three studies and the use of non-opioid substituted for opioid analgesic (Tramadol) in two studies. The diagnostic and cecal intubation rates ranged from 61.8% to 92.6% and from 67.3% to 98.2%, respectively. Only eight studies had record of ADR from histology with the ADR ranging from 1.0% to 28.8%. There was a paucity of data on the quality of bowel preparation, but documented cleansing agents are listed with other quality indices [Table 5]. No perforation or mortality was recorded, but a single case of post-polypectomy bleeding was recorded in two studies. Regional variations in CIR and PDR were statistically significant (P=0.043 and P=0.013, respectively) [Table 6].
Table 5: Quality indicators in colonoscopy studies

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Table 6: Regional comparison of polyp detection rate and cecal intubation rate

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Size, morphology, and location of polyps

Five studies documented details of morphology and four studies reported the size of polyps. Among the latter, majority of polyps were less than 1 cm in size and seen in studies from South-West and South-South Nigeria [Table 7]. In four out of the five studies mentioned, sessile morphology was predominant (72–85.7%). For location of polyps, an incomplete and heterogenous reporting style was noted and only nine studies reported location of detected polyps. This was categorized as rectum and other sites in one study; rectosigmoid and other sites in two studies; rectum, sigmoid colon, descending colon, and other sites in one study; individual separate segment identification as rectum, sigmoid colon, descending colon, transverse colon, ascending colon, and cecum in five studies. The rectosigmoid segment was reported with the highest frequency of 357 (43.1%) polyps [Table 8]. In the descending order of frequency of detection, the rectum, sigmoid colon, transverse colon, descending colon, ascending colon, and the cecum were involved.
Table 7: Size and morphology of polyps

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Table 8: Location of detected polyps

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Inflammatory polyps were the most common non-neoplastic polyps [174 (21.0%)]. A histopathology report of adenomas was recorded in 221 (26.7%) cases, but a significant proportion of this was unclassified (58.4%). Among the classified, tubular adenoma was most frequently recorded in 63/92 (68.5%) patients [Table 9].
Table 9: Histopathology of detected polyps

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  Discussion Top

There are large regional disparities in the PDRs among practicing Nigerian endoscopists ranging from mean rates of 7.5% in North-Central Nigeria to 38% in South-South Nigeria. The highest detection rate of colorectal polyps is found in Western countries, whereas the lowest in Africa and South-Central Asia.[29] Studies in referral tertiary hospitals in sub-Sahara Africa in patients with symptoms of colorectal pathologies report PDRs of 4.7%, 7.0%, 7.1%, 8.1%, and 25.2% from Ghana, Zambia, Sudan, Ethiopia, and Tanzania, respectively.[30],[31],[32],[33],[34] In two linked studies to investigate the prevalence and incidence of colorectal polyps from China, the prevalence of colorectal polyp at baseline was 18.1%, whereas almost one-fifth of the subjects developed colorectal polyps in the subsequent cohort study.[3] Their results indicated that risk factors for the presence of polyps included older age, male sex, regular smoking, and higher total serum cholesterol. In comparison to African and Asian studies, one large study from the USA documented that 44.9% of the polypectomies were performed on 17,275 patients who underwent average-risk screening colonoscopy.[35] Similarly, a high polyp detection/polypectomy rate as in the latter was reported in a sole Nigerian study on purely asymptomatic average risk individuals >45 years that comprised 93.9% males.[18] From available data, colorectal polyps were predominantly documented in male Nigerian patients aged >50 years. It is plausible that PDR will be higher with increasing average-risk screening colonoscopy for CRC in different parts of the country. This will primarily involve the middle-age population (above 50 years) observed to have more polyps in this review.

The three leading indications for colonoscopy were observed to be gastrointestinal bleeding, change in bowel habit, and abdominal pain in the decreasing order of frequency: 2760 (52.5%), 1148 (21.8%), and 733 (13.9%), respectively. Similarly, these indications are most frequently reported in African studies from Ghana, Ethiopia, and Sudan in sub-Saharan Africa.[30],[32],[36],[37] The common practice in Nigeria is evaluation of colon pathologies by barium enema studies. This test is limited in its sensitivity for the diagnosis of small mucosal lesions and prone to false positives, especially in cases of spasmic contraction and filling defects. Sigmoidoscopy and colonoscopy have the advantage of offering opportunities for therapeutic procedure in addition to affording more accurate diagnoses. Colonoscopy is more sensitive than sigmoidoscopy in view of extent of evaluation and detection of synchronous lesions. In the absence of a national screening program for CRC and a predominantly out-of-pocket paying practice for health services, a low rate of screening colonoscopy was observed, despite being the sixth leading indication [252 (4.8%)]. Again, this is like African reports on screening indication for LGIEs from Ghana and Ethiopia (1–1.7% and 5.3–8.1%, respectively).[30],[33],[36],[37] However, in the multiracial population of South Africa, screening for CRC is reported as the leading indication for colonoscopy (22.95%).[38]

A non-comprehensive colonoscopy reporting pattern was observed across studies, resulting in paucity of information on quality of colonoscopy. The critical element in the quality of colonoscopy regarding polyp detection and removal includes the performance of the endoscopist, independent of patient-related factors.[39] Notable quality metrics are cecal intubation rate (CIR), withdrawal time, adequacy of bowel preparation, and ADR. It is reported from a Western large-sized population study that in a normal daily colonoscopy practice, CIR is about 83% in symptomatic patients and rises to 95% in elective colonoscopy.[40] An observation from this study was that all cases with CIR <80% were in the study population of <150 patients [Table 5]. This can serve as a basis for a recommendation of trainee endoscopists performing 150 colonoscopies before certification in Nigeria. Training programs on insertion and withdrawal techniques are needed. A record of withdrawal time lasting > 6 min was available in three studies. The withdrawal technique rather than the withdrawal time has been suggested as the most important indicator that differentiated between endoscopists with varying ADRs.[41] High-rate detectors of polyps exhibit better performance including better examination behind every fold, adequate distension, cleansing, and time spent viewing the mucosa.[41] The more recent use of other mechanical enhancers of colonoscopy (caps, cuffs, and rings) is not documented in studies reviewed. Colonoscope with cap, cuff, or rings attached to its distal tip has been shown to increase the PDR and ADR, predominantly for the small polyps (<1 cm) and proximal colon location.[42] These adjuncts can improve outcome in our settings in which CIR and ADR are low.

There was a paucity of data on the quality of bowel preparation, with only three studies documenting adequacy of bowel preparation. Several international guidelines state that ≥ 85% of patients undergoing colonoscopy for screening /surveillance should have had a bowel preparation rated as least adequate.[43],[44] An adequate bowel preparation is one that maximizes the detection of mass lesions ≥5 mm during colonic examination.[45] The known risk factors reported for inadequate bowel preparation during colonoscopy include increasing age, male gender, medical history of colorectal surgery, diabetes mellitus, cirrhosis, inpatient status, and constipation.[46],[47],[48] Some other factors include a reported failure to successfully complete the bowel lavage, the use of tricyclic antidepressants, a history of stroke or dementia, a history of Parkinson’s disease, a later colonoscopy starting time during the day.[49] A case–control colonoscopy study on Nigerian patients identified those with low levels of education as more likely to have inadequate bowel preparation during colonoscopy.[50] Hence, there is a need for an effective patient education, especially for those with a low literacy level. There are different scales that have been developed for clinical or research purposes, to better quantify the adequacy of cleansing attributable to a bowel preparation. The Boston Bowel Preparation Scale and Aronchick were the ones used in the limited report of quality of bowel preparation in this review. A quality indicator issued by several international guidelines is that the endoscopist should report the quality of the bowel preparation for each colonoscopy.[51]

The screening detection and removal of precursor adenomatous polyp are known to reduce the mortality of CRC.[52] ADR describes the proportion of screening colonoscopies performed by a physician who detects at least one histologically confirmed colorectal adenoma.[53] In this review, we report a range of 1–28.8%. Ours is relatively lower compared with a range of 7.4–52.5% reported in the USA.[53] However, it is relatively comparable to 12% reported in South Africa.[54] Studies from Europe report ADR of 17.7% in France and 13.3–22.3% in Germany.[55],[56] It is expected that there are variations in the ADR reported in different countries including our report, as experiences vary with equipment, patient population, and the skills and techniques of the endoscopist. Improved technology or use of high definition colonoscope has been reported to improve ADR.[57],[58],[59],[60] ADR is observed to increase with each decade of life after 50 years.[35] In addition, personal history of adenoma and diabetes have been reported as probable predictive risk factors that increase ADR from a comparison of adenoma-positive patients with the adenoma-negative group.[53],[61] Genetic and immunosuppressive factors are culpable patient factors for adenoma formation.

The site and size of polyps are known predictors associated with the risk of malignancy. Right colonic lesions and polyps with large sizes are more associated with increased risk of malignancy.[62],[63] Adenomas that are 10 mm or more have higher risk of malignancy.[64],[65] Only a few studies in this review reported the size of polyp. Among those that reported, majority of polyps were less than 1 cm in size, seen in studies from South-West and South-South Nigeria. The finding of this review in terms of the size of polyp is similar to the report from Germany in which most of the polyps were 10 mm or less.[66] Similar observation is seen in a study in India.[67] In terms of location, less than half of the studies in this review described the site of occurrence of the polyps. In the descending order of frequency, it is the rectum, sigmoid colon, transverse colon, descending colon, ascending colon, and the cecum. These findings are similar to observations in South Asia[68] and Iran.[69] However, it differs from another study in Iran in which the sigmoid colon and the descending colon were found to be the commonest sites for polyps.[70] In the USA, African-Americans are more likely to have proximal polyps and tumors than their white counterparts.[71] The morphological characteristics of colorectal polyps are also associated with its risk of malignancy.[72],[73],[74],[75] About a third of the studies in the review described the morphology of the polyps, out of which sessile polyps followed by pedunculated polyps were more prevalent.

In this study, inflammatory polyps were found to be the most common non-neoplastic polyp. Chronic inflammation is associated with polypoid mass composed of reactive mucosal tissues. This is a common finding in patients with inflammatory bowel disease, which was thought to be of low prevalence in Africa, although recent studies have shown a rising trend.[76],[77] Another possible explanation for the findings in this study is a high prevalence of infectious agents in a developing country like Nigeria, which could result to prolonged inflammation and polyp formation.[78] Adenomas were the leading form of polyps seen. This is consistent with a South African study in which adenomas were found to be of higher prevalence than hyperplastic polyps (69.2% vs. 15.1%).[54] There may be a link between inflammatory and neoplastic lesions, especially when it is influenced by diet, gut microbiota, and other environmental factors.[79]


This systematic review is a collation and analysis of the work already done on colorectal polyps in Nigeria, with no unified colonoscopy reporting format. This has resulted in paucity of information in some needed areas and some outright missing data. The endoscopes used by the endoscopists also differ in type and sensitivity and hence may have relatively affected the output. The competence level of the endoscopists in Nigeria where gastrointestinal endoscopy practice is emerging may differ and hence may also have affected the findings used for this review. We could not determine if every polyp detected on colonoscopy was removed or not. There were different pathologists involved in the histopathologic evaluation of polyps in this study, like multiple endoscopists with different levels of experience, they may have affected the reportage.


The use of electronic health records with a national colonoscopy database will facilitate quality measurement, and reporting in Nigeria is recommended. Such quality-oriented registries should contain validated bowel preparation grades, polyp location, size, morphology, and histopathology of resected lesions with a note on post-polypectomy surveillance intervals. Secondly, as the burden of CRC increases, the debate is on regarding the ideal stool-based test for a preventive health policy in our clime. A significant level of false positivity on fecal immunohistochemistry due to endemic parasitic infestations is posited. There is the need for careful explanation of the various screening options and implication of positive test from stool- or radiology-based screening tests at the primary healthcare level for an individual choice to be made. A positive test result from the earlier mentioned investigations necessitates a colonoscopy for removal of polyps. Hence, in a targeted population, e.g., periodic medical evaluation for staff of multinational firms, individuals on premium health insurance packages, and affording out-of-pocket paying clients, colonoscopy can be recommended to patients as first choice screening investigation for CRC. Lastly, in view of the cost implication of colonoscopy service in a low-middle income setting, reliance on image enhancement technologies and fancy adjunct tools may not be widely implementable. However, additional training of Nigerian endoscopists on techniques to enhance polyp detection without adjunct tools is recommended. These techniques include adequate withdrawal time and techniques, training to recognize subtle polyps, right colon retroflexion, and dynamic position changes including training on techniques of advanced polyp resection.

  Conclusion Top

A large disparity exists in PDRs/ADRs among endoscopists in Nigeria with detected polyps more prevalent in distal colon of males aged >50 years and predominantly sessile in morphology. The training of Nigerian endoscopists on techniques to enhance CIR, polyp detection, and comprehensive documentation of quality metrics in colonoscopy studies is recommended.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]


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