Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (783 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
The terminal segment of the large intestine, beginning from the ampulla of the rectum and ending at the anus.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Anal Sphincter; Anal Sphincters; Sphincter, Anal; Sphincters, Anal; Anal Gland, Human; Human Anal Gland; Human Anal Glands; Anal Gland.
Where it fits in the MeSH classification
- Broader topics
- Intestine, Large
- See also
- Proctoscopy
Related concepts
- Large Intestine
- Rectum
Research landscape
PubMed indexes 21,656 records tagged with the MeSH heading “Anal Canal” (counts retrieved 2026-10-31). 3,414 of them (15.8%) were published from 2020 onward, and the busiest period so far is through 1999 with 8,664 records.
Reviews account for 2,077 records (9.6%) and meta-analyses for 200. Randomized controlled trials number 606 (2.8%) as a share of all records on the topic.
Show the data
| Period | Records |
|---|---|
| through 1999 | 8,664 |
| 2000-2009 | 3,859 |
| 2010-2019 | 5,719 |
| 2020 onward | 3,414 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 2,077 | 9.6% |
| Meta-analyses | 200 | 0.9% |
| Randomized controlled trials | 606 | 2.8% |
Method: PubMed query "Anal Canal"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-31.
Reading the evidence in anatomy and physiology
Anatomy describes how body structures are built and physiology describes how they normally work, so most findings here are descriptive or mechanistic rather than evidence about treatment. Much of what is known comes from dissection, imaging, tissue studies and experiments in animals, and measurements in healthy volunteers can differ from those in people with disease or at different ages. Normal ranges vary between individuals and populations. Check whether a result was measured in people or in another species, the age and health of the participants, and the method used.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Pelvic floor dysfunction one year after first childbirth in relation to perineal tear severity | 2021 | Research article Design not recorded in structured metadata | 50 | cc by PMID 34131194 · DOI · PMC8206367 |
| The London Classification: Improving Characterization and Classification of Anorectal Function with Anorectal Manometry | 2020 | Review article Design not recorded in structured metadata | 48 | cc by PMID 32935278 · DOI · PMC7497505 |
| Viral loads in throat and anal swabs in children infected with SARS-CoV-2 | 2020 | Research article Design not recorded in structured metadata | 33 | cc by PMID 32419639 · DOI · PMC7450259 |
| Caesarean section and anal incontinence in women after obstetric anal sphincter injury: A systematic review and meta-analysis | 2025 | Meta-analysis Design not recorded in structured metadata | 6 | cc by PMID 38965793 · DOI · PMC12137769 |
Pelvic floor dysfunction one year after first childbirth in relation to perineal tear severity [1]
Abstract reading summary — source excerpts
- Opening excerpt
- The aims of this study were to evaluate pelvic floor dysfunction symptoms one year after delivery and investigate whether adverse functional outcomes after childbirth were related to the degree of perineal injury.
- Closing excerpt
- Women with OASI had significantly higher risks of symptoms of prolapse, urge urinary incontinence, pain, dyspareunia and impacts on daily life.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (197 words)
The aims of this study were to evaluate pelvic floor dysfunction symptoms one year after delivery and investigate whether adverse functional outcomes after childbirth were related to the degree of perineal injury. A prospective cohort of 776 primiparas were included. Self-reported pelvic floor function data were obtained using a web-based questionnaire. Women with no/first-degree injuries, second-degree injuries, third-/fourth-degree injuries (obstetric anal sphincter injury, OASI) and cesarean section were compared. A total of 511 women (66%) responded. Second-degree tears were a risk factor for stress incontinence (aOR 2.6 (95% CI 1.3-5.1)). Cesarean section was protective against stress incontinence (aOR 0.2 (95% CI 0.1-0.9)). OASI was a risk factor for urge incontinence (aOR 4.8 (95% CI 1.6-15)), prolapse (aOR 7.7 (95% CI 2.1-29)) and pelvic pain (OR 3.3 (95% CI 1.1-10)). Dyspareunia was reported by 38% of women, 63% of women in the OASI group (aOR 3.1 (95% CI 1.1-9.0)). Women with OASI reported that the injury affected daily life (OR 18 (95% CI 5.1-59)). Pelvic floor dysfunction is common after childbirth, even in women with moderate injury. Women with OASI had significantly higher risks of symptoms of prolapse, urge urinary incontinence, pain, dyspareunia and impacts on daily life.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 34131194 · DOI · PMC8206367
The London Classification: Improving Characterization and Classification of Anorectal Function with Anorectal Manometry [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Purpose of reviewObjective measurement of anorectal sensorimotor function is a requisite component in the clinical evaluation of patients with intractable symptoms of anorectal dysfunction.
- Closing excerpt
- The London Classification is a standardized method and nomenclature for description of alterations in anorectal motor and sensory function using office-based investigations, adoption of which should bring much needed harmonization of practice.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (138 words)
Purpose of reviewObjective measurement of anorectal sensorimotor function is a requisite component in the clinical evaluation of patients with intractable symptoms of anorectal dysfunction. Regrettably, the utility of the most established and widely employed investigations for such measurement (anorectal manometry (ARM), rectal sensory testing and the balloon expulsion test) has been limited by wide variations in clinical practice.Recent findingsThis article summarizes the recently published International Anorectal Physiology Working Group (IAPWG) consensus and London Classification of anorectal disorders, together with relevant allied literature, to provide guidance on the indications for, equipment, protocol, measurement definitions and results interpretation for ARM, rectal sensory testing and the balloon expulsion test. The London Classification is a standardized method and nomenclature for description of alterations in anorectal motor and sensory function using office-based investigations, adoption of which should bring much needed harmonization of practice.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 32935278 · DOI · PMC7497505
Viral loads in throat and anal swabs in children infected with SARS-CoV-2 [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay on anal swabs was recently reported to be persistently positive even after throat testing was negative during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
- Closing excerpt
- These findings revealed that RT-PCR-testing on throat and anal swabs showed significant difference for monitoring SARS-CoV-2 infection and correlated with different immune state in paediatric patients.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (183 words)
Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay on anal swabs was recently reported to be persistently positive even after throat testing was negative during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, data about the consistent performance of RT-PCR assay on throat and anal swabs remain limited in paediatric patients. Here, we retrospectively reviewed RT-PCR-testing results of 212 paediatric patients with suspected SARS-CoV-2 infection at Wuhan Children's Hospital. The diagnostic potential of these two types of specimens showed significant difference (positive rate: 78.2% on throat swabs vs. 52.6% on anal swabs, McNemar Test P = 0.0091) and exhibited a weak positive consistency (Kappa value was 0.311, P P = 0.9511) and correlation (Pearson r = 0.0434, P = 0.8406), and exhibited an inconsistent kinetic change through the course of SARS-CoV-2 infection. Besides, viral loads in the throat and anal swabs were correlated with different types of immune states, immune-reactive phase, and the resolution phase/immunologic tolerance, respectively. These findings revealed that RT-PCR-testing on throat and anal swabs showed significant difference for monitoring SARS-CoV-2 infection and correlated with different immune state in paediatric patients.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 32419639 · DOI · PMC7450259
Caesarean section and anal incontinence in women after obstetric anal sphincter injury: A systematic review and meta-analysis [4]
Abstract reading summary — source excerpts
- Opening excerpt
- BackgroundApproximately 50% women who give birth after obstetric anal sphincter injury (OASI) develop anal incontinence (AI) over their lifetime.
- Closing excerpt
- Higher quality evidence is required to guide personalised decision-making for asymptomatic women and to determine the effect of subsequent birth mode on long-term AI outcomes.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (265 words)
BackgroundApproximately 50% women who give birth after obstetric anal sphincter injury (OASI) develop anal incontinence (AI) over their lifetime.ObjectiveTo evaluate current evidence for a protective benefit of planned caesarean section (CS) to prevent AI after OASI.Search strategyMEDLINE/PubMed, Embase 1974-2024, CINAHL and Cochrane to 7 February 2024 (PROSPERO CRD42022372442).Selection criteriaAll studies reporting outcomes after OASI and a subsequent birth, by any mode.Data collection and analysisEighty-six of 2646 screened studies met inclusion criteria, with nine studies suitable to meta-analyse the primary outcome of 'adjusted AI' after OASI and subsequent birth. Subgroups: short-term AI, long-term AI, AI in asymptomatic women.Secondary outcomestotal AI, quality of life, satisfaction/regret, solid/liquid/flatal incontinence, faecal urgency, AI in women with and without subsequent birth, change in AI pre- to post- subsequent birth.Main resultsThere was no evidence of a difference in adjusted AI after subsequent vaginal birth compared with CS after OASI across all time periods (OR = 0.92, 95% CI 0.72-1.20; 9 studies, 2104 participants, I2 = 0% p = 0.58), for subgroup analyses or secondary outcomes. There was no evidence of a difference in AI in women with or without subsequent birth (OR = 1.00 95% CI 0.65-1.54; 10 studies, 970 participants, I2 = 35% p = 0.99), or pre- to post- subsequent birth (OR = 0.79 95% CI 0.51-1.25; 13 studies, 5496 participants, I2 = 73% p = 0.31).ConclusionsDue to low evidence quality, we are unable to determine whether planned caesarean is protective against AI after OASI. Higher quality evidence is required to guide personalised decision-making for asymptomatic women and to determine the effect of subsequent birth mode on long-term AI outcomes.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 38965793 · DOI · PMC12137769
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article 3rd European Evidence-based Consensus on the Diagnosis and Management of Crohn's Disease 2016: Part 2: Surgical Management and Special Situations [5]
- Research article Anterior resection syndrome [6]
- Research article Epidemiology of anal human papillomavirus infection and high-grade squamous intraepithelial lesions in 29 900 men according to HIV status, sexuality, and age: a collaborative pooled analysis of 64 studies [7]
- Research article Meta-analysis to determine the incidence of obstetric anal sphincter damage [8]
- Research article Impact of ileal pouch-anal anastomosis on female fertility: meta-analysis and systematic review [9]
- Research article Perineal techniques during the second stage of labour for reducing perineal trauma [10]
References
- Huber M, Malers E, Tunón K. Pelvic floor dysfunction one year after first childbirth in relation to perineal tear severity. . 2021. PMID 34131194 · DOI · PMC8206367
- Scott SM, Carrington EV. The London Classification: Improving Characterization and Classification of Anorectal Function with Anorectal Manometry. . 2020. PMID 32935278 · DOI · PMC7497505
- Yuan C, Zhu H, Yang Y, Cai X, Xiang F, Wu H, et al.. Viral loads in throat and anal swabs in children infected with SARS-CoV-2. . 2020. PMID 32419639 · DOI · PMC7450259
- Carter E, Hall R, Ajoku K, Myers J, Kearney R. Caesarean section and anal incontinence in women after obstetric anal sphincter injury: A systematic review and meta-analysis. . 2025. PMID 38965793 · DOI · PMC12137769
- Gionchetti P, Dignass A, Danese S, Magro Dias FJ, Rogler G, Lakatos PL, et al.. 3rd European Evidence-based Consensus on the Diagnosis and Management of Crohn's Disease 2016: Part 2: Surgical Management and Special Situations. J Crohns Colitis. 2017. PMID 27660342 · DOI
- Bryant CL, Lunniss PJ, Knowles CH, Thaha MA, Chan CL. Anterior resection syndrome. Lancet Oncol. 2012. PMID 22935240 · DOI
- Wei F, Gaisa MM, D'Souza G, Xia N, Giuliano AR, Hawes SE, et al.. Epidemiology of anal human papillomavirus infection and high-grade squamous intraepithelial lesions in 29 900 men according to HIV status, sexuality, and age: a collaborative pooled analysis of 64 studies. Lancet HIV. 2021. PMID 34339628 · DOI · PMC8408042
- Oberwalder M, Connor J, Wexner SD. Meta-analysis to determine the incidence of obstetric anal sphincter damage. Br J Surg. 2003. PMID 14598410 · DOI
- Rajaratnam SG, Eglinton TW, Hider P, Fearnhead NS. Impact of ileal pouch-anal anastomosis on female fertility: meta-analysis and systematic review. Int J Colorectal Dis. 2011. PMID 21766164 · DOI
- Aasheim V, Nilsen ABV, Reinar LM, Lukasse M. Perineal techniques during the second stage of labour for reducing perineal trauma. Cochrane Database Syst Rev. 2017. PMID 28608597 · DOI · PMC6481402
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-31.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.