Editing Appendix (anatomy) (section)

== Structure ==
The human appendix averages {{convert|9|mm|in|abbr=on}} in length, ranging from {{convert|5|to|35|mm|in|abbr=on}}. The diameter of the appendix is {{convert|6|mm|in|abbr=on}}, and more than {{convert|6|mm|in|abbr=on}} is considered a thickened or inflamed appendix. The longest appendix ever removed was {{convert|26|cm|in|abbr=on}} long.<ref name="record">{{cite web |url=https://www.guinnessworldrecords.com/world-records/largest-appendix-removed |title=Largest appendix removed |date=26 August 2006 |publisher=[[Guinness World Records]] |access-date=22 May 2017 |url-status=live |archive-url=https://web.archive.org/web/20201126014839/https://www.guinnessworldrecords.com/world-records/largest-appendix-removed |archive-date=26 November 2020}}</ref> The appendix is usually located in the lower right [[quadrant (anatomy)|quadrant]] of the [[abdomen]], near the right [[iliac fossa|hip bone]]. The base of the appendix is located {{convert|2|cm|in|abbr=on}} beneath the [[ileocecal valve]] that separates the large intestine from the small intestine. Its position within the abdomen corresponds to a point on the surface known as [[McBurney's point]].

The appendix is connected to the [[mesentery]] in the lower region of the [[ileum]], by a short region of the [[mesentery|mesocolon]] known as the [[mesentery#Segments|mesoappendix]].<ref name="auto">{{cite journal |last1=Golalipour |first1=M.J. |last2=Arya |first2=B. |last3=Jahanshahi |first3=M. |last4=Azarhoosh |first4=R. |date=2003 |title=Anatomical Variations Of Vermiform Appendix In South-East Caspian Sea (Gorgan-IRAN) |url=https://medind.nic.in/jae/t03/i2/jaet03i2p141.pdf |journal=J. Anat. Soc. India |access-date=1 October 2014 |url-status=live |archive-url=https://web.archive.org/web/20200711120812/https://medind.nic.in/jae/t03/i2/jaet03i2p141.pdf |archive-date=11 July 2020}}</ref>

===Variation===
Some identical twins—known as [[Twin#Mirror image twins|mirror image twins]]—can have a [[situs inversus|mirror-imaged anatomy]], a [[congenital disorder|congenital condition]] with the appendix located in the lower left quadrant of the abdomen instead of the lower right.<ref>{{cite web|url=https://www.multiplesofamerica.org/research/unusual-types-of-twins/|title=Unusual Types of Twins|publisher=Multiples of America|url-status=dead|archive-url=https://web.archive.org/web/20140502001856/http://www.nomotc.org/index.php?option=com_content&task=view&id=59&Itemid=54|archive-date=2 May 2014|access-date=30 April 2014}}</ref><ref>{{cite journal | vauthors = Gedda L, Sciacca A, Brenci G, Villatico S, Bonanni G, Gueli N, Talone C | title = Situs viscerum specularis in monozygotic twins | journal = Acta Geneticae Medicae et Gemellologiae | volume = 33 | issue = 1 | pages = 81–5 | year = 1984 | pmid = 6540028 | doi = 10.1017/S0001566000007546 | doi-access = free }}</ref> [[Intestinal malrotation]] may also cause displacement of the appendix to the left side.

While the base of the appendix is typically located {{convert|2|cm|in|abbr=on}} below the [[ileocecal valve]], the tip of the appendix can be variably located—in the [[pelvis]], outside the [[peritoneum]] or behind the cecum.<ref name="Surgery">{{Cite book|author=Paterson-Brown, S. |chapter= 15. The acute abdomen and intestinal obstruction |editor1=Parks, Rowan W. |editor2=Garden, O. James |editor3=Carter, David John |editor4=Bradbury, Andrew W. |editor5=Forsythe, John L. R. |title=Principles and practice of surgery |publisher= Churchill Livingstone |location=Edinburgh |year=2007 |isbn=978-0-443-10157-1 |edition=5th}}</ref> The prevalence of the different positions varies amongst populations with the retrocecal position being most common in [[Ghana]] and [[Sudan]], with 67.3% and 58.3% occurrence respectively, in comparison to [[Iran]] and [[Bosnia]] where the pelvic position is most common, with 55.8% and 57.7% occurrence respectively.<ref>{{cite journal | vauthors = Clegg-Lamptey JN, Armah H, Naaeder SB, Adu-Aryee NA | title = Position and susceptibility to inflammation of vermiform appendix in Accra, Ghana | journal = East African Medical Journal | volume = 83 | issue = 12 | pages = 670–3 | date = December 2006 | pmid = 17685212 | doi = 10.4314/eamj.v83i12.9498 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Bakheit MA, Warille AA | title = Anomalies of the vermiform appendix and prevalence of acute appendicitis in Khartoum | journal = East African Medical Journal | volume = 76 | issue = 6 | pages = 338–40 | date = June 1999 | pmid = 10750522 }}</ref><ref>{{cite journal|vauthors=Ghorbani A, Forouzesh M, Kazemifar AM|year=2014|title=Variation in Anatomical Position of Vermiform Appendix among Iranian Population: An Old Issue Which Has Not Lost Its Importance|journal=[[Anatomy Research International]]|volume=2014|pages=313575|doi=10.1155/2014/313575|pmc=4176911|pmid=25295193|doi-access=free}}</ref><ref>{{cite journal | vauthors = Denjalić A, Delić J, Delić-Custendil S, Muminagić S | title = [Variations in position and place of formation of appendix vermiformis found in the course of open appendectomy] | language = bs | journal = Medicinski Arhiv | volume = 63 | issue = 2 | pages = 100–1 | year = 2009 | pmid = 19537667 }}</ref>

In very rare cases, the appendix may not be present at all ([[laparotomy|laparotomies]] for suspected appendicitis have given a frequency of 1 in 100,000).<ref>{{cite journal | vauthors = Zetina-Mejía CA, Alvarez-Cosío JE, Quillo-Olvera J | title = Congenital absence of the cecal appendix. Case report | journal = Cirugia y Cirujanos | volume = 77 | issue = 5 | pages = 407–10 | year = 2009 | pmid = 19944032 }}</ref>

Sometimes there is a semi-circular fold of [[mucous membrane]] at the opening of the appendix. This ''valve of the vermiform appendix'' is also called [[Joseph von Gerlach|Gerlach's]] valve.<ref name="auto"/>