This article provides a comprehensive list of anatomical variations, which are naturally occurring differences in human morphology. These variations are not considered defects or abnormalities but rather normal deviations that do not inherently indicate pathology. The frequencies in the tables below are mostly derived from meta-analyses. They are reported as percentage with 95% confidence intervals.
Head and neck Skeletal variations NameOther NamesDescriptionFrequencyAccessory maxillary ostiumsee Maxillary sinusArcuate foramen9.1% (8.2%—10.1%) Arcus praebasiocipitalisBasilar tubercle of clivus9.8%Canalis basilaris medianusClivus bony canalCollateral eminenceCondylus tertiusCraniopharyngeal canalForamen tympanicumFossa navicularis magnaHaller cellsee Ethmoid SinusInterparietal boneOs Interparietale, Inca boneInnominate canal of ArnoldIntermediate condylar canalOs odontoideum0.21%, (0.00%—0.72%)Ossiculum terminale (of dens)Bergmann's ossicleOssified petrosphenoid ligamentSagittal keelSphenoethmoidal air cellOnodi cellsee Sphenoid sinusStafne bone cavity0.17% (0.14%—0.21%)Thyroid foramensee Thyroid cartilage24.5% (19.2—29.8%)Transverse basilar fissureSaucer's fissuresee ClivusTubercle at the anterior rim of foramen magnumWormian bonesSutural bones
Muscular variations NameOther NamesDescriptionFrequencyAccessory slip of levator palpebrae superiorisAccessory belly of Digastric muscleAtlantomastoid muscleCleidoatlanticus muscleCleidocervical muscleCleidofascialis muscleCleidohyoideus muscleCleidomastoideus muscleCleidooccipitalis cervicalis muscleCricocorniculate muscleCricohyoid musclevariation of thyrohyoidLevator claviculae muscleLevator glandulae thyroidealevator muscle of thyroid glandPterygoideus proprius muscleSternoclavicularis anticus muscleStyloauricularis muscleTransversus nuchae muscle
Vascular variations NameOther NamesDescriptionFrequencyPersistent primitive olfactory arteryArtery of PercheronStapedial arteryThyroid ima artery3.8% (2.7%—4.9%)Fourth thyroid veinFourth thyroid vein of Kochersee Inferior thyroid veinsFalcine sinusHypoglossal arteryPersistent left superior vena cavaTrigeminal artery
Nervous variations NameOther NamesDescriptionFrequencyAberrant facial nerve courseAccessory hypoglossal nerveTrigeminal nerve duplication
Other variations NameOther NamesDescriptionFrequencyAnisocoriaCrease of the upper eyelidSingle or Double eyelidEmpty sella turcicaEpicanthic foldDarwin's tubercleDiagonal earlobe creasePreauricular sinusZuckerkandl's tuberclePyramidal lobe of thyroid gland
Vertebral column Skeletal variations NameOther NamesDescriptionFrequencyAtlanto-occipital fusionsee Atlanto-occipital joint0.64% (0.00%–1.00 %)Atlas arch defectOssification anomalies of the atlasBlock vertebraeButterfly vertebraeCervical ribsCoccygeal ribsDiastematomyeliaSplit cord malformationLumbosacral transitional vertebraeOppenheimer's ossicleSagittal cleft vertebraeSpondylolisthesisSpondylolysisSprengel's deformityhigh scapula, scapular hypoplasia
Thorax Skeletal variations +NameOther namesDescriptionFrequencyBifid ribBifid xiphoid processsee Xiphoid processEpisternal ossiclesManubriosternal fusionsee SternumSternal cleftSternal foramenSternoxiphoidal fusionXiphoid foramen
Muscular variations NameOther namesDescriptionFrequencySternalis muscleRectus ThoracisCostocoracoideus muscle
Other variations NameOther namesDescriptionFrequencyAzygos lobe of the lungCardiac bronchussee BronchusHorseshoe lungSupernumerary lung fissuresSupernumerary nippleTracheal bronchussee Bronchus
Upper limb Skeletal variations NameOther namesDescriptionFrequencyBifurcated clavicleBipartite capitateCoracoclavicular jointCarpal bossCarpal coalitionOs acromialesee AcromionScapular foramina and tunnelsSupracondylar process of the humerus
Muscular variations NameOther namesDescriptionFrequencyAccessory subscapularis muscleAxillary arch muscleChondroepitrochlearis musclesee Pectoralis majorCoracocapsularis muscleCostodeltoideus muscleEpitrochleoanconeus muscleAnconeus epitrochlearisExtensor carpi radialis tertius muscleExtensor carpi radialis accessoriusExtensor digitorum brevis manus muscleExtensor indicis et medii communis muscleExtensor medii proprius muscleExtensor pollicis et indicis communis muscleFlexor carpi radialis profundus muscleLinburg-Comstock variationTendinous conjunction of the Flexor Pollucis Longus and Flexor Digitorum Profundus20.3% ( 14.3%–27.0%)Palmaris profundus musclePisiuncinatus musclePisohamateSternochondrocoracoideus muscleSternohumeralis muscleSubclavius posticusChondroscapularisSubscapularis minor muscleUlnaris quinti muscleTensor semivaginae articulations humeroscapularis muscleThoracobrachialis muscle
Vascular variations NameOther namesDescriptionFrequencyAlar thoracic arteryMedian artery12.2% (6.5%–19.2%)Superficial ulnar arteryVariation of the basilic vein
Nervous variations +NameOther namesDescriptionFrequencyBifid median nervesee Median nerveBerrettini anastomosisFroment-Rauber nerveMartin-Gruber anastomosisNerve of McKenzieRiché-Cannieu anastomosis
Other variations NameOther namesDescriptionFrequencyAccessory nail of the fifth toeOsborne's ligamentStruthers' ligament
Lower limb Skeletal variations NameOther namesDescriptionFrequencyAccessory naviculaCalcaneonavicular coalitionCyamellaSesamoid in the Popliteus muscle tendon.FabellaSesamoid bone in the lateral head of the Gastrocnemius muscle.Femoral anteversion/retroversionOs tibiale externumOs trigonumTalocalcaneal coalitionTalus accessorius
Muscular variations NameOther namesDescriptionFrequencyAccessory popliteus muscleAccessory soleus muscleAdductor minimus muscleFibularis quartus musclePeroneus quartusGastrocnemius tertius musclesee Gastrocnemius muscleGluteoperinealis muscleGluteus quartus musclefibulocalcaneus internus musclePeroneocalcaneus internusPopliteus biceps muscleTensor fasciae suralis muscle
Vascular variations NameOther namesDescriptionFrequencyCorona Mortissee Obturator artery
Abdomen
Muscular variations NameOther namesDescriptionFrequencyInterfoveolar musclePubotransversalis muscleSaphenous muscle
Vascular variations NameOther namesDescriptionFrequencyArc of BühlerBühler's anastomotic arteryMarginal artery of the colonMarginal artery of DrummondThird mesenteric artery
Other variations +NameOther namesDescriptionFrequencyAccessory spleenAccessory pancreatic ductAgenesis of vermiform appendixsee Appendix (anatomy)Annular pancreasBifid pancreas tailColon duplicationDouble common bile ductGastropancreatic ligamentPancreas divisum
Pelvis Vascular variations NameOther namesDescriptionFrequencyUterine artery anastomoses variations
Other variations NameOther namesDescriptionFrequencyBladder exstrophyHirsuties coronae glandisHorseshoe kidney (Ren arcuatus)Renal artery anomaliesSplenogonadal fusionSupernumerary ovaries
References