{{Short description|Proposed human anatomical structure}} The '''rectosigmoid junction''', formerly the '''rectosigmoid sphincter''' or '''sphincter of O'Beirne''', is the junction of the sigmoid colon and the rectum.<ref name=":0" />
== Hypothesized sphincter ==
The rectosigmoid sphincter, also known as the ''sphincter of O'Beirne'', was hypothesized as an anatomical structure located between the sigmoid colon and rectum.<ref name=":0" /> The structure was first proposed by the 19th-century Irish surgeon James O'Beirne. Its existence, structure and function has been a matter of long-standing medical controversy.<ref name=":0">{{Cite journal |last=Ballantyne |first=G. H. |date=August 1986 |title=Rectosigmoid sphincter of O'Beirne |journal=Diseases of the Colon and Rectum |volume=29 |issue=8 |pages=525–531 |doi=10.1007/BF02562612 |issn=0012-3706 |pmid=3525042}}</ref><ref>{{Cite journal |last1=Chen |first1=Ji-Hong |last2=Nirmalathasan |first2=Sharjana |last3=Pervez |first3=Maham |last4=Milkova |first4=Natalija |last5=Huizinga |first5=Jan D. |date=October 2021 |title=The Sphincter of O'Beirne - Part 1: Study of 18 Normal Subjects |journal=Digestive Diseases and Sciences |volume=66 |issue=10 |pages=3516–3528 |doi=10.1007/s10620-020-06657-w |issn=1573-2568 |pmid=33462748}}</ref> The Latin names ''sphincter ani tertius'' and ''pylorus sigmoidrectalis'' also been used.<ref name=":1">{{Cite book |last1=Steele |first1=Scott R. |url=https://books.google.com/books?id=IBVQEAAAQBAJ&pg=PA18 |title=The ASCRS Textbook of Colon and Rectal Surgery |last2=Hull |first2=Tracy L. |last3=Hyman |first3=Neil |last4=Maykel |first4=Justin A. |last5=Read |first5=Thomas E. |last6=Whitlow |first6=Charles B. |date=2021-11-20 |publisher=Springer Nature |isbn=978-3-030-66049-9 |pages=18 |language=en}}</ref><ref>{{Cite web |title=sphincter ani tertius |url=https://medical-dictionary.thefreedictionary.com/sphincter+ani+tertius |access-date=2025-10-30 |website=Farlex Partner Medical Dictionary |language=en}}</ref>
{{As of|2025}}, the existence of some form of distinct contractile anatomical structure at the rectosigmoid junction, if not an actual sphincter, in many people is acknowledged in numerous articles in the medical literature.<ref name=":1" /><ref name=":0" /><ref>{{Cite journal |last1=Trzpis |first1=Monika |last2=Sun |first2=Ge |last3=Chen |first3=Ji-Hong |last4=Huizinga |first4=Jan D. |last5=Broens |first5=Paul |date=January 2023 |title=Novel insights into physiological mechanisms underlying fecal continence |url=https://journals.physiology.org/doi/full/10.1152/ajpgi.00313.2021 |journal=American Journal of Physiology. Gastrointestinal and Liver Physiology |volume=324 |issue=1 |pages=G1–G9 |doi=10.1152/ajpgi.00313.2021 |pmid=36283962 |issn=0193-1857|hdl=11370/f16949ad-100a-4bba-8267-9948d15e0234 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Shafik |first1=Ahmed |last2=Mostafa |first2=Randa M. |last3=Shafik |first3=Ali A. |date=2002 |title=Electrophysiological study of the rectosigmoid canal: evidence of a rectosigmoid sphincter |journal=Journal of Anatomy |language=en |volume=200 |issue=5 |pages=517–521 |doi=10.1046/j.1469-7580.2002.00049.x |issn=1469-7580 |pmc=1570712 |pmid=12090397}}</ref><ref>{{Cite journal |last1=Shafik |first1=A. |last2=Doss |first2=S. |last3=Asaad |first3=S. |last4=Ali |first4=Y. A. |date=November 1999 |title=Rectosigmoid junction: anatomical, histological, and radiological studies with special reference to a sphincteric function |journal=International Journal of Colorectal Disease |volume=14 |issue=4–5 |pages=237–244 |doi=10.1007/s003840050217 |issn=0179-1958 |pmid=10647633}}</ref><ref>{{Cite journal |last1=Shafik |first1=Ahmed |last2=Asaad |first2=Soheir |last3=Doss |first3=Sameh |date=March 2003 |title=Identification of a sphincter at the sigmoidorectal canal in humans: histomorphologic and morphometric studies |journal=Clinical Anatomy |volume=16 |issue=2 |pages=138–143 |doi=10.1002/ca.10054 |issn=0897-3806 |pmid=12589668}}</ref><ref>{{Cite journal |last1=Shafik |first1=Ahmed |last2=Shafik |first2=Ali A. |last3=Sibai |first3=Olfat El |last4=Ahmed |first4=Ismail |last5=Mostafa |first5=Randa M. |date=2006-01-01 |title=Role of the Rectosigmoidal Junction in Fecal Continence: Concept of the Primary Continent Mechanism |url=https://jamanetwork.com/journals/jamasurgery/fullarticle/397885 |journal=Archives of Surgery |language=en |volume=141 |issue=1 |pages=23–26 |doi=10.1001/archsurg.141.1.23 |pmid=16415407 |issn=0004-0010 |archive-url=https://web.archive.org/web/20230610004123/https://jamanetwork.com/journals/jamasurgery/fullarticle/397885 |archive-date=2023-06-10|url-access=subscription }}</ref><ref>{{Cite journal |last=Shafik |first=A. |date=April 1997 |title=The hypertonic rectosigmoid junction: description of a new clinicopathologic entity causing constipation |journal=Surgical Laparoscopy & Endoscopy |volume=7 |issue=2 |pages=116–120 |doi=10.1097/00019509-199704000-00009 |issn=1051-7200 |pmid=9109239}}</ref>
The junction is made up of circular and longitudinal muscle fascia<ref name=":4">{{Cite journal |last1=Massalou |first1=Damien |date=2018-04-01 |title=Is it possible to give a single definition of the rectosigmoid junction? |journal=Surgical and Radiologic Anatomy |volume=40 |issue=4 |pages=431–438 |doi=10.1007/s00276-017-1954-4 |issn=1279-8517 |last2=Moszkowicz|first2=David|last3=Mariage|first3=Daniela|last4=Baqué|first4=Patrick|last5=Camuzard|first5=Olivier|last6=Bronsard|first6=Nicolas|pmid=29218384 |url=https://doi.org/10.1007/s00276-017-1954-4|language=en|url-access=subscription}}</ref>. Like many of our other digestive system’s sphincters: Upper esophageal sphincter (UES) <ref>{{Citation |last=Mittal|first=Ravinder K.|title=Upper Esophageal Sphincter|date=2011|work=Motor Function of the Pharynx, Esophagus, and its Sphincters|url=https://www.ncbi.nlm.nih.gov/books/NBK54282/|access-date=2026-03-27|publisher=Morgan & Claypool Life Sciences|language=en}}</ref>, pyloric sphincter <ref>{{Citation |title=Pylorus|date=2025-07-06|work=Wikipedia|url=https://en.wikipedia.org/w/index.php?title=Pylorus&oldid=1299175962|access-date=2026-03-27|language=en}}</ref>, sphincter of Oddi; this junction may have a high-pressure zone mimicking our digestive systems’ sphincter-like functions <ref>{{Cite journal |last1=Shafik|first1=Ahmed|last2=Mostafa|first2=Randa M.|last3=Shafik|first3=Ali A.|date=2002|title=Electrophysiological study of the rectosigmoid canal: evidence of a rectosigmoid sphincter|journal=Journal of Anatomy|language=en|volume=200|issue=5|pages=517–521|doi=10.1046/j.1469-7580.2002.00049.x|issn=1469-7580|pmc=1570712|pmid=12090397}}</ref>.The RSJ may also play a role in regulating stool passage by increasing rectal pressure and thereby preventing premature reflux of rectal contents back into the sigmoid colon<ref name=":02">{{Cite journal |date=August 1986 |title=Rectosigmoid sphincter of O'Beirne |journal=Diseases of the Colon and Rectum |volume=29 |issue=8 |pages=525–531 |doi=10.1007/BF02562612 |pmid=3525042 |issn=0012-3706|last=Ballantyne|first=G. H.}}</ref>. However, this functional role of the rectosigmoid junction is yet to be considered as a distinct anatomical sphincter.
== Molecular signature of rectosigmoid junction cancer == A 2023 study suggested that cancers of the rectosigmoid junction exhibit different chemical signatures from either cancers of the colon or cancers of the rectum.<ref>{{Cite journal |last1=Zhu |first1=Qiuwei |last2=Zhu |first2=Chenyang |last3=Zhang |first3=Xiaotao |last4=Zhu |first4=Xiaodan |last5=Chen |first5=Zhe |last6=Gu |first6=Dejian |last7=He |first7=Yuange |last8=Jin |first8=Chunhui |date=2023-06-30 |title=Comprehension of rectosigmoid junction cancer molecular features by comparison to the rectum or sigmoid colon cancer |journal=Journal of Gastrointestinal Oncology |volume=14 |issue=3 |pages=1307–1319 |doi=10.21037/jgo-23-120 |doi-access=free |issn=2078-6891 |pmc=10331759 |pmid=37435233}}</ref>
'''Clinical Significance'''
The junction is important in clinical practices, especially in the classification and management of colorectal diseases and colorectal cancer. Due to its variable definition of sigmoid and rectal pathology of whether to classify tumors in this region as colorectal cancer or rectal cancer, it may complicate diagnostic approaches and treatments in cancer .<ref>{{Cite journal |last1=D'Souza |first1=Nigel |last2=de Neree tot Babberich |first2=M.P.M |last3=Lord |first3=Amy |last4=Shaw |first4=Annabel |last5=Abulafi |first5=Muti |last6=Tekkis |first6=Paris |last7=Wiggers |first7=Theo |last8=Brown |first8=Gina |date=September 2018 |title=The rectosigmoid problem |url=https://linkinghub.elsevier.com/retrieve/pii/S0960740417303936 |journal=Surgical Oncology |language=en |volume=27 |issue=3 |pages=521–525 |doi=10.1016/j.suronc.2018.06.005 |pmid=30217314 |url-access=subscription }}</ref>
The taenia coli of the colon spreads out to form a continuous longitudinal muscle layer around the rectum, approximately 12-15 cm from the anal verge.<ref>{{Citation |last1=Wang |first1=Yun Hwa W. |title=Anatomy, Abdomen and Pelvis, Rectum |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK537245/ |access-date=2026-04-05 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30725930 |last2=Wiseman |first2=Jeffrey}}</ref>
Research indicates that RSJ cancers can have a higher propensity for synchronous liver metastasis and lymphovascular invasion when compared to tumors in the sigmoid or upper rectum<ref name=":2">{{Cite journal |last1=Falch|first1=Claudius|last2=Mueller|first2=Sven|last3=Braun|first3=Manuel|last4=Gani|first4=Cihan|last5=Fend|first5=Falko|last6=Koenigsrainer|first6=Alfred|last7=Kirschniak|first7=Andreas|date=2019-11-01|title=Oncological outcome of carcinomas in the rectosigmoid junction compared to the upper rectum or sigmoid colon – A retrospective cohort study|url=https://www.sciencedirect.com/science/article/pii/S0748798319305189|journal=European Journal of Surgical Oncology|volume=45|issue=11|pages=2037–2044|doi=10.1016/j.ejso.2019.06.024|pmid=31239157 |issn=0748-7983|url-access=subscription}}</ref>.
In a retrospective cohort study, the five-year survival rate for patients with carcinomas as the RSJ was significantly lower than that of patients with tumors in the sigmoid colon or upper rectum<ref name=":2" />. However, other large-scale registry data show that when adjusted for comorbidities in patients, RSJ and rectal cancers could have slightly better survival chances than proximal colon cancers in specific demographics<ref name=":3">{{Cite journal |last1=Yu|first1=Shou-Chun|last2=Liao|first2=Kuang-Ming|last3=Chou|first3=Chia-Lin|last4=Tian|first4=Yu-Feng|last5=Wang|first5=Jhi-Joung|last6=Ho|first6=Chung-Han|last7=Shiue|first7=Yow-Ling|date=2022|title=Impact of Tumor Location on Survival in Patients With Colorectal Cancer: A Retrospective Cohort Study Based on Taiwan's Cancer Registry Database|journal=Clinical Medicine Insights. Oncology|volume=16|article-number=11795549221111713|doi=10.1177/11795549221111713|issn=1179-5549|pmc=9301104|pmid=35875416}}</ref>.
== References == {{reflist}}
== See also == * Taenia coli
Category:Human anatomy Category:Muscular system Category:Large intestine Category:Rectum
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