Editing Conjoined twins (section)

== {{anchor|Types of conjoined twin}}Types ==
Conjoined twins are typically classified by the point at which their bodies are joined. The most common types of conjoined twins are:
* ''Thoracopagus'' (28% of cases):<ref name=embryology/> Two bodies fused from the upper chest to the lower chest. These twins usually share a [[heart]] and may also share the [[liver]] or part of the [[digestive system]].<ref name="duplicata">{{cite web|url=http://www.thefetus.net/page.php?id=1494|date=March 1, 2006|archive-url=https://web.archive.org/web/20090819191053/http://www.thefetus.net/page.php?id=1494|archive-date=August 19, 2009|title=Duplicata incompleta, dicephalus dipus dibrachius|first=Yuliya|last=Burmagina|website=TheFetus.net}}</ref> Survival rate is poor.<ref name=":1">{{Cite web |title=Conjoined Twins: Definition, Causes & Outlook |url=https://my.clevelandclinic.org/health/diseases/22895-conjoined-twins |access-date=2023-12-15 |website=Cleveland Clinic |language=en}}</ref>
* ''Thoraco-omphalopagus'' (18.5%):<ref name=embryology/> Two bodies fused from the upper chest to lower belly. The heart is always shared in these cases.<ref name=duplicata/> {{As of|2015}}, twins who share a heart have not been able to both survive separation; a designated twin who is allotted the heart may survive if the other twin is sacrificed.
* ''Omphalopagus'' (10%):<ref name=embryology/> Two bodies fused at the lower abdomen. Unlike thoracopagus, the heart is not shared; however, the twins often share a liver, a digestive system, a [[diaphragm (anatomy)|diaphragm]] and other organs.<ref name=duplicata/> Survival rate is 82%.<ref name=":1" />
* ''Heteropagus''<ref>{{Cite journal |last1=Sharma |first1=Gaurav |last2=Mobin |first2=Sheila S. Nazarian |last3=Lypka |first3=Michael |last4=Urata |first4=Mark |date=December 2010 |title=Heteropagus (parasitic) twins: a review |url=https://pubmed.ncbi.nlm.nih.gov/21129567/ |journal=Journal of Pediatric Surgery |volume=45 |issue=12 |pages=2454–2463 |doi=10.1016/j.jpedsurg.2010.07.002 |issn=1531-5037 |pmid=21129567}}</ref> ([[parasitic twin]]) (10%):<ref name=embryology/> Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin's organs for survival.
* ''[[Craniopagus twins|Craniopagus]]'' (6%):<ref name=embryology/> Fused [[human skull|skull]]s, but separate bodies. These twins' heads may be conjoined at the back, front, or side of the head, but not on the face or at the base of the skull.<ref name=duplicata/> Survival rate is poor.<ref name=":1" />

Other, less common types of conjoined twins include:
* ''Cephalopagus'': Two faces on opposite sides of a single, conjoined head; the upper portion of the body is fused while the bottom portions are separate. These twins generally cannot survive due to severe malformations of the brain. This is also known as janiceps (after the two-faced Roman deity [[Janus (mythology)|Janus]]).<ref name=duplicata/>
* ''Syncephalus'': One head with a single face but four ears and two bodies.<ref name=duplicata/>
* ''Cephalothoracopagus'': Bodies fused at the head and thorax, with two faces facing in opposite directions, or sometimes with a single face and an enlarged skull.<ref name=duplicata/><ref>{{cite web |url=http://www.collphyphil.org/virt_tour/museum_8.htm |title=Cephalothoracopagus Menosymmetro (Conjoined Twins) |website=collphyphil.org| publisher= Mütter Museum, The College of Physicians of Philadelphia |access-date=2014-08-03 |url-status=dead |archive-url= https://web.archive.org/web/20100815054642/http://www.collphyphil.org/virt_tour/museum_8.htm |archive-date=2010-08-15 }}</ref>
* ''Xiphopagus'': Two bodies fused in the [[Xiphoid process|xiphoid cartilage]], which extends approximately from the navel to the lower breastbone. These twins almost never share any vital organs, with the exception of the liver.<ref name=duplicata/> A famous example is [[Chang and Eng Bunker]].
* ''[[Ischiopagi|Ischiopagus]]'': Fused lower half of the two bodies, with [[Vertebral column|spines]] conjoined end-to-end at a 180° angle. These twins have four arms; one, two, three or four legs; and typically one set of external [[genitalia]] and one [[Human anus|anus]].<ref name=duplicata/> Survival rate is 63%.<ref name=":1" />
* ''Omphalo-Ischiopagus'': Fused in a similar fashion to ischiopagus twins, but facing each other, with a joined abdomen, akin to omphalopagus. These twins have four arms, and two, three, or four legs.<ref name=duplicata/>
* ''Parapagus'': Fused side by side with a shared [[human pelvis|pelvis]]. Those that are ''dithoracic parapagus'' are fused at the abdomen and pelvis, but not at the thorax. Those that are ''[[diprosopic parapagus]]'' have one trunk and two faces. Those that are ''[[dicephalic parapagus]]'' have one trunk and two heads, and may have two (dibrachius), three (tribrachius), or four (tetrabrachius) arms.<ref name=duplicata/> Survival rate is poor.<ref name=":1" />
* ''[[Craniopagus parasiticus]]'': Like craniopagus, but with a second bodiless head attached to the dominant head.
* ''Pygopagus'' or ''Iliopagus'': Two bodies joined at the pelvis.<ref name=duplicata/> Survival rate is 68%.<ref name=":1" />
* ''Rachipagus'': Twins joined along the back of their bodies, with fusion of the vertebral arches and the soft tissue from the head to the buttocks.<ref>{{cite journal |last1=Spencer |first1=Rowena |title=Rachipagus conjoined twins: They really do occur! |journal=Teratology |date=December 1995 |volume=52 |issue=6 |pages=346–356 |doi=10.1002/tera.1420520605 |pmid=8711621 }}</ref> Twins of this type cannot be separated.<ref name=":1" />
* ''Tricephalus'' (conjoined triplets): Extremely rare conjoining of 3 fetuses. Very few confirmed cases, both human and animal, are known.<ref>{{Cite journal |last1=Oostra |first1=Roelof-Jan |last2=Schepens-Franke |first2=Annelieke N. |last3=Magno |first3=Giovanni |last4=Zanatta |first4=Alberto |last5=Boer |first5=Lucas L. |date=2022-07-15 |title=Conjoined twins and conjoined triplets: At the heart of the matter |journal=Birth Defects Research |language=en |volume=114 |issue=12 |pages=596–610 |doi=10.1002/bdr2.2066 |pmid=35766259 |pmc=9546242 |s2cid=250114880 |issn=2472-1727|doi-access=free }}</ref>