View source for Situs inversus

{{Infobox_Disease |
  Name           = Situs inversus |
  Image          = Situs inversus 1.jpg |
  Caption        = Situs inversus; heart and stomach on the right; vena cava and liver on the left |
  DiseasesDB     = 29885 |
  ICD10          = {{ICD10|Q|89|3|q|80}} |
  ICD9           = {{ICD9|759.3}} |
  ICDO           = |
  OMIM           = 270100 |
  MedlinePlus    = |
  eMedicineSubj  = radio |
  eMedicineTopic = 639 |
  MeshID         = D012857 |
}}
{{SI}}
{{CMG}}

==Overview==
'''Situs inversus''' (also called '''situs transversus''') is a rare [[Congenital disorder|congenital condition]] in which the major [[viscera]]l [[Organ (anatomy)|organs]] are reversed or mirrored from their normal positions. The normal arrangement is known as ''situs solitus''. In other rare cases, in a condition known as [[situs ambiguus]] or heterotaxy, situs cannot be determined.

The term ''situs inversus'' is a short form of the [[Latin]] phrase "''situs inversus viscerum''," meaning "inverted position of the internal organs."  [[Dextrocardia]] (the [[heart]] being located on the right side of the [[thoracic cavity|thorax]]) was first recognised by Marco Severino in 1643.  However, situs inversus was first described more than a century later by [[Matthew Baillie]].

The prevalence of situs inversus varies among different populations but is less than 1 in 10,000 people.<ref>[http://www.emedicine.com/radio/topic639.htm Situs inversus] on [[eMedicine]]</ref>

== Anatomy ==
[[Image:Situs inversus - Mirrored heart and lungs.jpg|thumb|left|160px|Situs inversus causes the positions of the [[heart]] and [[lungs]] to be mirrored.]]
The condition affects all major structures within the [[thoracic cavity|thorax]] and [[abdomen]]. Generally, the organs are simply transposed through the [[sagittal plane]]. 

The heart is located on the right side of the thorax, the [[stomach]] and [[spleen]] on the right side of the abdomen and the [[liver]] and [[gall bladder]] on the left side. 

The left lung is trilobed and the right lung bilobed, and [[blood vessel]]s, [[nerve]]s, [[lymph vessels|lymphatic]]s and the [[intestine]]s are also transposed.

If the heart is swapped to the right side of the thorax, it is known as ''situs inversus with [[dextrocardia]]'' or ''situs inversus totalis''.  

If the heart remains in the normal left side of the thorax, a much rarer condition (1 in 22,000 cases of situs inversus), it is known as ''situs inversus with [[levocardia]]'' or ''situs inversus incompletus''. 

Situs inversus with [[levocardia]], or [[dextrocardia]] without situs inversus, present much higher rates of congenital defects than situs inversus with dextrocardia.

== Significance ==

Situs inversus is generally an [[Recessive gene|autosomal recessive]] [[genetics|genetic]] condition, although it can be [[X-linked]] or found in identical "mirror" [[twins]].<ref>[Gedda L, Sciacca A, Brenci G, Villatico S, Bonanni G, Gueli N, Talone C. Situs viscerum specularis in monozygotic twins. Acta Genet Med Gemellol (Roma) 1984; 33(1): 81-5.]</ref>  

In the absence of congenital heart defects, individuals with situs inversus are [[phenotype|phenotypically]] unimpaired, and can lead normal healthy lives, without any complications related to their medical condition.  

There is a 5-10% prevalence of [[congenital heart disease]] in individuals with situs inversus totalis, most commonly [[transposition of the great vessels]]. The incidence of congenital heart disease is 95% in situs inversus with levocardia.

Many people with situs inversus are unaware of their unusual anatomy until they seek medical attention for an unrelated condition. The reversal of the organs may then lead to some confusion, as many signs and symptoms will be on the 'wrong' side. 

For example, if an individual with situs inversus develops [[appendicitis]], they will present to the physician with left lower abdominal pain, since that is where their appendix lies. Thus, in the event of a medical problem, the knowledge that the individual has situs inversus can expedite diagnosis.  People with this rare condition should inform their [[physician]]s before an examination, so they may redirect their search for [[heart sound]]s and other [[sign (medicine)|signs]]. 

Situs inversus also complicates [[organ transplantation]] operations as donor organs will almost certainly come from situs solitus donors.  As hearts and livers are [[chiral]], geometric problems arise placing an organ into a cavity shaped in the mirror image. 

For example, a person with situs inversus who requires a heart transplant needs all the vessels to the transplant donor heart reattached to their existing ones. However, the orientation of these vessels in a person with situs inversus is reversed, necessitating steps so that the blood vessels join properly.

== Kartagener syndrome ==
[[Image:autorecessive.jpg|thumb|120px|left|Situs inversus is generally inherited in an [[Recessive gene|autosomal recessive]] pattern.]]
{{see|primary ciliary dyskinesia}}
About 25% of individuals with situs inversus have an underlying condition known as [[primary ciliary dyskinesia]] (PCD). 

PCD is a dysfunction of the [[cilium|cilia]] that manifests itself during the embryologic phase of development. 

Normally-functioning cilia determine the position of the internal organs during early [[mammalian embryogenesis|embryological development]], and so individuals with PCD have a 50% chance of developing situs inversus. 

If they do, they are said to have Kartagener syndrome, characterized by the triad of situs inversus, chronic [[sinusitis]], and [[bronchiectasis]]. 

Cilia are also responsible for clearing [[mucus]] from the lung, and the dysfunction causes increased susceptibility to lung infections. 

Male sufferers of PCD are often infertile: the cilia that make up the tail of individual sperm cells are also defective, thus rendering the sperm ineffective.

==Diagnosis==
===Chest x ray===
[[Image:SitusInversus.jpg]]

==See also==
* [[Situs solitus]]
* [[Situs ambiguus]]
* [[Asplenia]]
* [[Polysplenia]]

==Notes==
{{Reflist|2}}

==References==
{{refbegin|2}}
* {{cite book
 | last = McManus
 | first = Chris 
 | year = 2002
 | title = Right Hand, Left Hand
 | publisher = Harvard University Press
 | id = ISBN 0-674-00953-3
}} this book was the 2003 Aventis winner and has a description of the history behind the discovery of this medical condition.
* {{cite journal |author=Yokoyama T, Copeland NG, Jenkins NA, Montgomery CA, Elder FF, Overbeek PA |title=Reversal of left-right asymmetry: a situs inversus mutation |journal=Science |volume=260 |issue=5108 |pages=679-82 |year=1993 |pmid=8480178 |doi=10.1126/science.8480178}}
* {{cite journal |author=Lowe LA, Supp DM, Sampath K, ''et al'' |title=Conserved left-right asymmetry of nodal expression and alterations in murine situs inversus |journal=Nature |volume=381 |issue=6578 |pages=158-61 |year=1996 |pmid=8610013 |doi=10.1038/381158a0}}
* {{cite journal |author=Levin M |title=Left-right asymmetry in vertebrate embryogenesis |journal=Bioessays |volume=19 |issue=4 |pages=287-96 |year=1997 |pmid=9136626 |doi=10.1002/bies.950190406}}
* {{cite journal |author=Levin M, Pagan S, Roberts DJ, Cooke J, Kuehn MR, Tabin CJ |title=Left/right patterning signals and the independent regulation of different aspects of situs in the chick embryo |journal=Dev. Biol. |volume=189 |issue=1 |pages=57-67 |year=1997 |pmid=9281337 |doi=10.1006/dbio.1997.8662}}
* {{cite journal |author=Logan M, Pagán-Westphal SM, Smith DM, Paganessi L, Tabin CJ |title=The transcription factor Pitx2 mediates situs-specific morphogenesis in response to left-right asymmetric signals |journal=Cell |volume=94 |issue=3 |pages=307-17 |year=1998 |pmid=9708733 |doi=10.1016/S0092-8674(00)81474-9}}
* {{cite journal |author=Stern CD, Wolpert L |title=Left-right asymmetry: all hands to the pump |journal=Curr. Biol. |volume=12 |issue=23 |pages=R802-3 |year=2002 |pmid=12477404 |doi=10.1016/S0960-9822(02)01312-X}}
{{refend}}

==External links==
*[http://www.laughs.com.au/sid/ Situs Inversus site with discussion forum]
* {{Chorus|00698}}

{{Phakomatoses and other congenital malformations not elsewhere classified}}
{{SIB}}

[[Category:Genetic disorders]]
[[Category:Cardiology]]
[[Category:Disease state]]
[[Category:Mature chapter]]

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[[ja:全臓器反転症]]
[[nl:Situs inversus]]
[[ru:Транспозиция органов]]
[[sq:Situs inversus]]

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