Variation archive

854 published articles

• Encyclopedia entry9 August 2026

  Splenic Artery

  When the splenic artery divides terminally near the spleen (~1-2 cm from the hilus) it is called a magistral splenic. This occurs in about 30% of individuals. When the division of the splenic occur earlier, as in about 70% of individuals, in the prepancreatic segment, it is called a distributing splenic. The variations of the splenic artery are numerous. It may divide into two branches that reunite, the splenic vein passing through the loop thus formed. It may give rise to branches normally derived from other vessels, such as the left gastric, middle colic, and left hepatic.

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• Encyclopedia entry9 August 2026

  Common Iliac Artery

  The common iliac arteries are as short as 1.2 cm or as long as 11 cm; the usual length is 3.7-7.5 cm in 72% of individuals studied. The remaining 28% were divided equally, being longer or shorter than usual length.These variations in length may depend on whether the aorta bifurcates above or below the usual point, or on whether the common iliac arteries divide higher or lower than usual. A low aortic bifurcation is more common than a high bifurcation, as is also the case with the common iliacs. The bifurcation of the common iliacs varies.

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• Encyclopedia entry9 August 2026

  Radial Recurrent Artery

  The radial recurrent artery may be absent, in which case it may be replaced by a branch of the superior ulnar collateral artery that crosses over the humerus to reach the lateral side of the elbow.

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• Encyclopedia entry9 August 2026

  Pulmonary Artery

  The pulmonary artery (carrying deoxygenated blood) may appear as a branch at the origin of the arch of the ascending aorta. Conversely, the aorta may be a branch of the pulmonary trunk (subject living 20 years) or even a branch of the right ventricle (subject living 13 years). The right branch of the pulmonary artery is occasionally doubled, with the second branch arising from the right ventricle. A pulmonary artery may be absent. The right and left branches may be doubled. The left branch may provide a branch to the left subclavian, and the right a branch to the brachiocephalic trunk.

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• Encyclopedia entry9 August 2026

  Popliteal Artery

  Bardsley and Staple report variations in the branches of the popliteal occurred in 7.2% of 235 limbs. The small number of variations are, nonetheless, clinically significant. If the branching pattern is "normal" (usual) in one limb, there is an 8% chance that the contralateral limb will have a variant. If one limb has a variant there is a 50% chance that the other limb will also be variable.

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• Encyclopedia entry9 August 2026

  Middle Cerebral Artery

  In a study of 25 brains (50 middle cerebral arteries), 10 forms of division were found. The principal forms of variation included: a) a single vessel arising proximal to the sylvian fissure (34%), b) more than one major vessel arising proximal to the sylvian fissure (26%), c) a trifurcation at the mouth of the sylvian fissure (34%), and d) a bifurcation at the mouth of the sylvian fissure (16%). The middle cerebral may be absent or replaced by a branch from the deep cerebral.

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• Encyclopedia entry9 August 2026

  Posterior Communicating Artery

  This artery may be absent or replaced by a branch from the middle cerebral. In one review of nine studies of 2362 brains, the posterior communicating artery was absent unilaterally in 3.09% and bilaterally in 0.3%. The posterior communicating artery is sometimes joined with the middle cerebral artery instead of the trunk of the internal carotid.

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• Encyclopedia entry9 August 2026

  Peroneal Artery

  The peroneal artey was found to be well-developed in 31 of 209 cadavers, about 15% of legs. It may arise (unusually) in the distal leg. It may also be absent or replaced by the posterior tibial. On occasion it gives rise to the anterior tibial, or rejoins the posterior tibial. An accessory peroneal artery has also been noted.

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• Encyclopedia entry9 August 2026

  Profunda Femoris Artery

  This artery may course lateral, medial or anterior to the femoral artery. If it arises from the medial aspect of the femoral, the femoral may appear to split into three vessels of almost equal caliber: femoral, profunda and lateral circumflex. Srb (1860) though that its position depended on whether it furnished the medial circumflex or not; the lateral circumflex tends to draw the profunda laterally. The profunda may pass medially superficial to the vein, and then continue in its usual way.

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• Encyclopedia entry9 August 2026

  Thoracoacromial Artery

  The thoracoacromial artery may be missing. In Poynter's series it was the second branch in 47% of individuals studied. In some cases the arteries that make up the trunk arise separately, and in other cases it may have four branches; supreme (superior) thoracic, thoracic branch of the thoracoacromial, accessory pectoral branches, and lateral thoracic. The thoracoacromial artery may send a branch to pectoralis minor (8%) This artery may have a common origin with some other artery in 24% of individuals.

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• Encyclopedia entry9 August 2026

  Obturator Artery

  This artery has received much attention due to its surgical interest connected with its origin from the epigastric artery. Poynter suggested that the first report of the origin of the obturator from the epigastric was that of Haller, 1745, note 9, who says ,"Non tamen perpetuum est cam arteriam a pelves truncis nasci, eam novies ex epigastrica ortam." Further that the surgical significance of the epigastric source seems to have been recognized by Monro in 1806.

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• Encyclopedia entry9 August 2026

  Middle Rectal Artery

  This artery may be absent. It may arise from the internal iliac with the inferior vesical artery. It has also been reported as arising with or from the internal pudendal, or inferior gluteal arteries. Unusual branches of the middle rectal include: the vaginal, seminal vesical, prostatic, and inferior lateral sacral arteries. In their report to the anatomical society of Great Britian and Ireland, Parsons and Keith, provided the following data. They had 45 observations.

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• Encyclopedia entry9 August 2026

  Middle Meningeal Artery

  The middle meningeal artery may be absent. In 99% of cases however, it enters the foramen spinosum. When this foramen is absent, the artery enters the foramen ovale , which is typically the foramen for the mandibular division of the trigeminal nerve. The middle meningeal gives rise, in about 50% of cases, to an accessory meningeal artery, which also enters the skull via the foramen ovale, or the emissary sphenoidal foramen (20% of cases). It may also supply a palatine branch.

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• Encyclopedia entry9 August 2026

  Middle Sacral Artery (Median Sacral)

  The middle sacral artery may deviated from the midline. It may arise in common with one or both of the fifth pair of lumbar arteries, or from the bifurcation of the aorta, or from one of the iliac arteries, more frequently from the left. It often provides, from each side, a large branch (the lowest lumbar artery), which courses backwards onto the fifth lumbar vertebra (see illustration from Tiedemann). The middle sacral artery may also provide an "accessory" renal or, a middle rectal artery. The middle sacral artery may also provide a renal artery in cases of pelvic kidney.

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• Encyclopedia entry9 August 2026

  Lumbar Arteries

  One or more pairs of the lumbar arteries may arise as a common stem from the back of the aorta. The first lumbar may be joined at its origin with the lowest intercostal artery; the third and fourth lumbar, or less often the second and third lumbars, may arise from the aorta as a common stem. The fifth pair is sometimes absent. One or both of the last pair of lumbar arteries may arise in common with the middle sacral.

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• Encyclopedia entry9 August 2026

  Lateral Thoracic Artery

  This artery may arise from the thoracoacromial (12% of individuals, Poynter). The lateral thoracic may be replaced by or it may replace the thoracodorsal. On rare occasions it gives rise to the ulnar artery, and itself may be a branch of the subscapular (8%, Poynter). In about 24% of individuals the lateral thoracic is doubled. Poynter found the distribution to the intercostal spaces to be irregular; the second space received no supply in 15% and the axillary sent another branch to supply this intercostal space in 17%.

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• Encyclopedia entry9 August 2026

  Medial and Lateral Femoral Circumflex Arteries

  Variations of the medial femoral circumflex artery include the following. It may arise from the profunda femoris before the lateral circumflex; from the femoral artery, external iliac (2%) or one of its branches, or superficial epigastric; or from the the inferior epigastric artery or it may be the source of the inferior epigastric. The artery of ligamentum teres femoris arises from the medial femoral circumflex in about 15% of cases, from the obturator and medial circumflex via an anastomotic connection in about 24%, and from both arteries independently in about 7%.

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• Encyclopedia entry9 August 2026

  Ulnar Artery

  The ulnar artery may arise from the brachial above the usual point of division or from the axillary, in which case it usually passes over the flexor muscles, but beneath the fascia, to reach its usual position in the forearm. In circumstances such as this, the artery may terminate in the proximal forearm with a persistent median artery supplying the superficial arch The recurrent arteries and the common interosseous are usually derived from the trunk vessel from which the ulnar arises.

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• Encyclopedia entry9 August 2026

  Lateral Internal Thoracic Artery

  The internal thoracic may give rise to a lateral internal thoracic as it enters the thorax. The lateral internal thoracic runs about midway between the spine and the sternum or somewhat forward, spans up to six intercostal spaces, and anastomoses with the intercostal arteries of those spaces. A lateral internal thoracic artery may arise from the costocervical trunk, thyrocervical trunk, or ascending cervical. The possible existence of this vessel must be remembered when paracentesis is performed.

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• Encyclopedia entry9 August 2026

  Variations in the Branches of the Subclavian Artery

  There is considerable variation in the branching of the subclavian artery, and the branches may be arranged differently on the two sides of the body. The usual branching order on the right side is for the vertebral, thyrocervical trunk (common trunk for the inferior thyroid, transverse cervical, and suprascapular arteries, in 50% of cases), and the internal thoracic (internal mammary) to arise from the first part of the right subclavian.

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