{{Short description|Difference between the anatomical structures}} An '''anatomical variation''', '''anatomical variant''', or '''anatomical variability''' is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categorized into three types including morphometric (size or shape), consistency (present or absent), and spatial (proximal/distal or right/left).<ref>{{Cite journal |last=Yammine |first=Kaissar |date=2014 |title=Evidence-Based Anatomy |journal=Clinical Anatomy |volume=27 |issue=6 |pages=847–852 |doi=10.1002/ca.22397 |issn=0897-3806 |pmc=4282349 |pmid=24797314}}</ref>
Variations are seen as normal in the sense that they are found consistently among different individuals, are mostly without symptoms, and are termed anatomical variations rather than abnormalities.<ref name="Atlases">{{cite web |title=Anatomic variants |url=https://www.anatomyatlases.org/AnatomicVariants/Introduction.shtml}}</ref>
Anatomical variations are mainly caused by genetics and may vary considerably between different populations. The rate of variation considerably differs between single organs, particularly in muscles.<ref name="Atlases"/> Knowledge of anatomical variations is important in order to distinguish them from pathological conditions.
A very early paper published in 1898, presented anatomic variations to have a wide range and significance,<ref name="Cunningham">{{cite journal |last1=Cunningham |first1=DJ |title=The Significance of Anatomical Variations. |journal=Journal of Anatomy and Physiology |date=October 1898 |volume=33 |issue=Pt 1 |pages=1–9 |pmid=17232348|pmc=1327970 }}</ref> and before the use of X-ray technology, anatomic variations were mostly only found on cadaver studies. The use of imaging techniques have defined many such variations.<ref name="Bell">{{cite web |last1=Bell |first1=Daniel J. |title=Anatomical variants {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/anatomical-variants?lang=gb |website=Radiopaedia}}</ref>
Some variations are found in different species such as polydactyly, having more than the usual number of digits.
==Variants of structures== {{Main|List of anatomical variations}} ===Muscles=== Kopsch gave a detailed listing of muscle variations. These included the absence of muscles; muscles that were doubled; muscles that were divided into two or more parts; an increase or decrease in the origin or insertion of the muscle; and the joining to adjacent organs.<ref name="Atlases"/>
The palmaris longus muscle in the forearm is sometimes absent, as is the plantaris muscle in the leg.<ref name="Saladin2">{{cite book |last1=Saladin |first1=K |title=Anatomy and Physiology |date=2012 |isbn=9780073378251 |pages=14–15 |publisher=McGraw-Hill Education |edition=6th}}</ref>
The sternalis muscle is a variant that lies in front of the pectoralis major and may show up on a mammogram.<ref>{{Cite web|url=https://radiopaedia.org|title=Sternalis muscle|last=Garg|first=T|website=radiopaedia.org|access-date=19 September 2019}}</ref>
===Bones=== Usually there are five lumbar vertebrae but sometimes there are six, and sometimes there are four.<ref name="Saladin2"/>
===Joints=== A discoid meniscus is a rare thickened lateral meniscus in the knee joint that can sometimes be swollen and painful.<ref name="Kim">{{cite journal |last1=Kim |first1=JG |last2=Han |first2=SW |last3=Lee |first3=DH |title=Diagnosis and Treatment of Discoid Meniscus. |journal=Knee Surgery & Related Research |date=2016-12-01 |volume=28 |issue=4 |pages=255–262 |doi=10.5792/ksrr.16.050 |pmid=27894171|pmc=5134787 |doi-access=free }}</ref>
===Organs=== The lungs are subject to anatomical variations.<ref name="Moore">{{cite book |last1=Moore |first1=K |title=Clinically oriented anatomy |date=2018 |isbn=9781496347213 |page=342 |publisher=Wolters Kluwer |edition=Eighth}}</ref>
==See also== * Supernumerary body part * Visible difference
==References== {{Reflist}}
==External links== * [http://www.anatomyatlases.org/AnatomicVariants/AnatomyHP.shtml Atlas of human anatomical variations]
Category:Anatomy Category:Anatomical variations