List of anatomical variations

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.

Head and neck

Skeletal variations

• Occipitalization of the atlas
• Basilar tubercle of clivus
• Clivus bony canal
• Condylus tertius
• Epipteric bone
• Foramen tympanicum
• Ossified petrosphenoid ligament
• Ossification anomalies of the atlas (C1)
• Craniopharyngeal canal
• Canalis basilaris medianus
• Fossa navicularis magna
• Transverse basilar fissure (Saucer's fissure) (see Clivus)
• Arcus praebasiocipitalis
• Stafne bone cavity
• Arcuate foramen
• Ossiculum terminale (of dens)
• Os odontoideum
• Intermediate condylar canal
• Innominate canal of Arnold
• Arcus praebasiocipitalis
• Inca bone
• Haller cell
• Sphenoethmoidal air cell (Onodi cell) (see Sphenoid sinus)
• Accessory maxillary ostium (see Maxillary sinus)
• Thyroid foramen (see Thyroid cartilage)
• Collateral eminence
• Wormian bones

Muscular variations

• Levator glandulae thyroidea (levator muscle of thyroid gland)
• Accessory belly of digastric muscle (see Digastric muscle)
• Atlantomastoid muscle^[1]
• Styloauricularis muscle^[2]
• Transversus nuchae muscle
• Pterygoideus proprius muscle
• Levator claviculae muscle
• Levator glandulae thyroidea muscle
• Cleidoatlanticus muscle
• Cleidocervical muscle
• Cleidofascialis muscle
• Cleidohyoideus muscle
• Cleidomastoideus muscle
• Cleido-occipitalis cervicalis muscle
• Cricocorniculate muscle
• Cricohyoid muscle (variation of thyrohyoid)
• Sternoclavicularis anticus muscle
• Styloauricularis muscle

Vascular variations

• Persistent primitive olfactory artery
• Artery of Percheron
• Stapedial artery
• Thyroid ima artery
• Fourth thyroid vein (of Kocher) (see Inferior thyroid veins)
• Falcine sinus
• Hypoglossal artery
• Persistent left superior vena cava
• Trigeminal artery

Nervous variations

• Trigeminal nerve duplication
• Aberrant facial nerve course
• Accessory hypoglossal nerve

Other variations

• Preauricular sinus
• Supernumerary nipple
• Darwin's tubercle
• Anisocoria
• Diagonal ear lobe crease
• Empty sella turcica
• Epicanthic fold
• Crease of the upper eyelid (Single or Double eyelid)
• Zuckerkandl's tubercle
• Pyramidal lobe of thyroid gland

Vertebral column and ribs

Skeletal variations

• Atlanto-occipital fusion (see Atlanto-occipital joint)
• Butterfly vertebrae
• Cervical ribs
• Coccygeal ribs
• Block vertebrae
• Sagittal cleft vertebrae
• Lumbosacral transitional vertebrae
• Split cord malformation
• Sternal cleft
• Spondylolisthesis
• Oppenheimer's ossicle
• Spondylolysis
• Sprengel's deformity

Thorax

Skeletal variations

• Sternal foramen and xiphoid foramen
• Episternal ossicles
• Manubriosternal fusion (see Sternum)
• Sternoxiphoidal fusion
• Bifid xiphoid process (see Xiphoid process)
• Bifid rib

Muscular variations

• Sternalis muscle (rectus thoracis)
• Costocoracoideus  muscle

Other variations

• Azygos lobe of the lung
• Tracheal bronchus (see Bronchus)
• Cardiac bronchus (see Bronchus)
• Supernumerary lung fissures
• Horseshoe lung

Upper limb

Skeletal variations

• Bifurcated clavicle
• Coracoclavicular joint
• Os acromiale (see Acromion)
• Carpal coalition
• Carpal boss
• Bipartite capitate
• Supracondylar process of the humerus
• Scapular foramina and tunnels

Muscular variations

• Accessory subscapularis muscle
• Gantzer's muscle (see Flexor pollicis longus muscle)
• Chondroepitrochlearis muscle (see Pectoralis major)
• Coracocapsularis muscle
• Costodeltoideus muscle
• Axillary arch muscle
• Epitrochleoanconeus (anconeous epitrochlearis) muscle
• Extensor medii proprius muscle
• Extensor digitorum brevis manus muscle
• Extensor indicis et medii communis muscle
• Extensor pollicis et indicis communis muscle
• Extensor carpi radialis tertius (extensor carpi radialis accessorius) muscle
• Linburg-Comstock variation (conjoint flexor pollicis longus and flexor digitorum profundus of the index)
• Palmaris profundus muscle
• Flexor carpi radialis profundus muscle
• Ulnaris quinti muscle
• Pisiuncinatus muscle (pisohamatus)
• Sternohumeralis muscle
• Sternochondrocoracoideus muscle
• Subscapularis minor muscle
• Tensor semivaginae articulations humeroscapularis muscle
• Thoracobrachialis muscle^[3]

Vascular variations

• Alar thoracic artery
• Median artery
• Superficial ulnar artery
• Variation of the basilic vein

Nervous variations

• Bifid median nerve (see Median nerve)
• Nerve of McKenzie
• Martin-Gruber anastomosis
• Riché-Cannieu anastomosis
• Berrettini anastomosis
• Froment-Rauber nerve

Other variations

• Accessory nail of the fifth toe
• Osborne's ligament
• Struthers' ligament

Lower limb

Skeletal variations

• Femoral anteversion/retroversion
• Os tibiale externum
• Fabella (popliteal sesamoid)
• Calcaneonavicular coalition
• Accessory navicula
• Talocalcaneal coalition
• Cyamella (popliteal fabella)
• Sesamoid bone of the second, third, fourth, and fifth finger
• Talus accessorius
• Os trigonum

Muscular variations

• Accessory soleus muscle
• Accessory popliteus muscle
• Adductor minimus muscle
• Tensor fasciae suralis muscle
• Gastrocnemius tertius muscle (see Gastrocnemius muscle)
• Gluteoperinealis muscle
• Gluteus quartus muscle
• Popliteus biceps muscle
• Fibularis (peroneus) quartus muscle
• Peroneocalcaneus internus muscle

Vascular variations

• Marginal artery of the colon
• Corona mortis (see Obturator artery)

Nervous variations

• Sciatic nerve variations in relation to the piriformis muscle

Abdomen

Muscular variations

• Interfoveolar muscle
• Saphenous muscle
• Pubotransversalis muscle

Vascular variations

• Arc of Bühler
• Third mesenteric artery
• Marginal artery of the colon (of of Drummond)

Other variations

• Accessory spleen
• Annular pancreas
• Bifid pancreas tail
• Double common bile duct
• Agenesis of vermiform appendix (see Appendix (anatomy))
• Colon duplication
• Accessory pancreatic duct
• Pancreas divisum
• Gastropancreatic ligament

Pelvis

Vascular variations

• Uterine artery anastomoses variations

Other variations

• Bladder exstrophy
• Renal artery anomalies
• Splenogonadal fusion
• Supernumerary ovaries
• Horseshoe kidney (Ren arcuatus)
• Hirsuties coronae glandis

References

1. Lee, Rebecca; Pang, Stephen C.; Borman, William H.; Herrin, Sean O.; Bale, Logan S. W. (2022-10-01). "A prevalence study of the atlantomastoid muscle". Surgical and Radiologic Anatomy. 44 (10): 1349–1353. doi:10.1007/s00276-022-03022-6. ISSN 1279-8517. PMID 36155834.
2. Touré, Gaoussou; Anzouan-Kacou, Evelyne (2016-10-01). "The styloauricular muscle: clinical relevance and literature review of this rare muscle". Surgical and Radiologic Anatomy. 38 (8): 983–986. doi:10.1007/s00276-016-1633-x. ISSN 1279-8517. PMID 26846137.
3. Zielinska, Nicol; Karauda, Piotr; Węgiel, Andrzej; Szewczyk, Bartłomiej; Olewnik, Łukasz (2023-11-01). "A very rare case of a thoracobrachialis muscle". Surgical and Radiologic Anatomy. 45 (11): 1493–1496. doi:10.1007/s00276-023-03240-6. ISSN 1279-8517. PMC 10587252. PMID 37733018.