Variation archive

854 published articles

• Encyclopedia entry9 August 2026

  Persistent Embryologic Arteries (Hyaloid, Hypoglossal, Stapedial, and Trigeminal)

  Occasionally, arteries that are found during embryologic development, that usually disappear, persist. The primitive trigeminal artery is the most common persistent carotid-basilar anastomic channel observed in adult life and has been reported as an incidental finding in 0.1 to 0.6% of consecutive cerebral angiograms or autopsy cases. See also text and references given for the Ophthalmic, Hyaloid, and Lacrymal arteries and for the Anterior Inferior Cerebellar , the Posterior inferior Cerebellar arteries , the internal carotid and the vertebral arteries .

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• Encyclopedia entry9 August 2026

  Portal Vein

  The portal vein is rarely variable. It often receives the left gastric vein, and may also receive an accessory splenic, inferior phrenic branch, pancreaticoduodenal, a pulmonary vein or right gastroepiploic vein. The hepatoduodenal ligament constitutes the anterior margin of the foramen of Winslow and enclosed the common bile duct, hepatic artery, and portal vein. Usually, the the hepatic artery is located to the left of the common bile duct, and the portal vein is situated posterior and between these two structures (Marois, et al.).

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• Encyclopedia entry9 August 2026

  Heart

  Congenital cardiac anomalies are seen in 0.6% of live births and in 2.0% of stillbirths. Common cardiac anomalies are: a) atresia or stenosis of the pulmonary trunk or aorta, b) defective closure of septal openings, c) defective closure of the ductus arteriosus, d) reverse rotation of the heart and, e) mirror imaging. Situs inversus are examples of d and e. Incomplete closure of the foramen ovale, "probe patency," is common (~25% of adult hearts) and may be regarded as a normal variant rather than an abnormality. The foramen is closed physiologically but patent anatomically.

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• Encyclopedia entry9 August 2026

  Inferior Vesical Artery

  The inferior vesical may arise in common with the middle rectal, or from a common trunk with the internal pudendal and superior gluteal or as a branch from the internal pudendal. It is usually a single branch. Anastomoses between the inferior vesical and uterine arteries were found in 60-70% of subjects reported. In the report of the Committee of Collective Investigation of the Anatomical Society of Great Britian and Ireland, Parsons and Keith reported on 58 observations of the inferior vesical artery.

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• Encyclopedia entry9 August 2026

  Lateral Sacral Artery

  Usually the second branch of the posterior division of the internal iliac, these vessels show great irregularity in development, according to Poynter. They represent two separate vessels, a superior and an inferior vessel. They are frequently associated with the superior gluteal artery in early development, a condition that is reflected in adult statistics (in 92% of cases, Parsons). Poynter found the lateral sacral single in 55%, doubled in 45%, and arising from the hypogastric (internal iliac) in 22%. These vessels from both sides may arise in common.

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• Encyclopedia entry9 August 2026

  Femoral Vein

  The femoral vein may be doubled in part of, or throughout its length. It may split into two and encircle the femoral artery. It occasionally passes through the adductor magnus above the femoral artery and runs independently from the artery until it joins the profunda vein to form the common femoral vein. The femoral may run with the sciatic nerve and pierce the the adductor magnus at the level of the lesser trochanter. When this occurs, the femoral artery is usually small, and the inferior gluteal (sciatic) artery is the primary (developmental) vessel of the thigh.

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• Encyclopedia entry9 August 2026

  Dorsospinal Artery

  A dorsospinal artery from the aorta may supply the anterior spinal artery but it has been rarely reported. The dorsospinal artery has been reported three times, 1) on the right side at the T9 level, 2) once on the left at the T10 level, and 3) on the right side at the T8 level. An isolated dorsospinal artery has been found to supply the anterior spinal artery in only two cases. In one of the cases, the anterior spinal artery had a dual blood supply. A recent angiographic study by Lefournier, et al.

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• Encyclopedia entry9 August 2026

  Great Saphenous Vein

  The entrance of veins into the great saphenous vein most commonly includes the superficial epigastric, superficial circumflex iliac, the lateral accessory saphenous which forms a common trunk and the external pudendal vein which drains into the great saphenous independently.

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• Encyclopedia entry9 August 2026

  External Iliac Artery

  The external iliac may be longer or shorter than usual, resulting from the bifurcation of the common iliac above or below its usual point. When longer, it often takes a tortous course, making a partial loop or bend that may take it below the brim of the pelvis. The artery may be much smaller in diameter than usual; this may be the case when the femoral or main vessel of the lower limb arises from the inferior gluteal or other branch of the internal iliac. It then often terminates in profunda femoris.

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• Encyclopedia entry9 August 2026

  Deep Circumflex Iliac Artery

  The circumflex iliac may arise (a) like the epigastric, from the external iliac higher than usual, although seldom, if ever, as high as the epigastric; (b) more rarely, from the femoral below the inguinal ligament, or as a common trunk with the epigastric. It may be absent, doubled or tripled. The deep circumflex iliac occasionally arises in common with the inferior epigastric or from the femoral artery. This artery may give rise to the external pudendal and medial femoral circumflex, and may provide muscular branches in place of the lateral femoral circumflex. External Pudendal Superficial

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• Encyclopedia entry9 August 2026

  Circle of Willis

  This circle of anastomosing arterial vessels is extremely variable. Stehbens regards a normal circle of Willis to be one in which there is a complete anastomotic polygon, which may show considerable variability not only of its components but also its branches. The so-called normal or textbook description holds true in about 34.5% of cases based on a composit review of 1413 brains. Not even Willis's original illustration conforms to the usual textbook description. See illustrations for Circle variations.

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• Encyclopedia entry9 August 2026

  Costocervical Trunk Arteries

  The trunk commonly arises from the third part of the subclavian. This artery is inconstant (absent in 30-40%) of individuals and may arise from other parts of the subclavian. The usual branches are: superior (supreme) intercostal and the deep cervical. It is found on the right side in 75% of cases and occurs on the left in only 30% of humans. It is absent in 8-10% of cases, and thus its main branches may arise independently, most frequently from the second part of the subclavian.

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• Encyclopedia entry9 August 2026

  Recurrent Artery of Heubner

  Descriptions of the origin of the recurrent artery are inconsistent. Most of these vessels arise from the A-2 segment of the anterior cerebral artery (i.e., the segment in the interhemispheric fissure, distal to the anterior communicating artery) within 2 or 3 mm of the anterior communicating artery. However, it may arise as far as 1.0 cm proximal to the anterior communicating artery. The recurrent artery is rarely absent and is rarely doubled.

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• Encyclopedia entry9 August 2026

  Right Gastric Artery

  The most frequent origin of the right gastric artery is the proper hepatic artery (~ 53%); the common hepatic, near its point of division (~20%); or from the left hepatic branch (~15%). In some cases it arose as a branch of the gastroduodenal (~8%), or as a branch of the common hepatic (~4 %). Daseler et al. (1947) provide the following concise summary: Origin of right gastric artery: 250 cases; proper hepatic, 125; left hepatic, 81; gastroduodenal, 33; right hepatic, 10; celiac, 1.

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• Encyclopedia entry9 August 2026

  Posterior Cerebral Artery

  Occasionally, the proximal part of one of the posterior cerebral arteries is greatly reduced in size. The blood reaches the terminal region of the vessel from the internal carotid via the posterior communicating artery. The posterior cerebral may course below, rather than over, the oculomotor nerve (cranial nerve 3). It may be absent and replaced by an accessory contralateral vessel. The posterior cerebral may provide the anterior cerebral artery.

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• Encyclopedia entry9 August 2026

  Anterior Inferior Cerebellar and Posterior Inferior Cerebellar Arteries

  One of the anterior inferior or posterior inferior arteries may be missing. Occasionally, one of the anterior inferior cerebellar arteries arises from the posterior cerebellar artery. The posterior inferior cerebellar artery may provide the posterior spinal artery. The posterior inferior cerebellar artery may arise from the internal carotid artery and the embryonic explanation postulated is the persistence of a primitive communicating vessel (presegmental artery) between the anterior and posterior circulation.

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• Encyclopedia entry9 August 2026

  Ophthalmic, Hyaloid, and Lacrimal Arteries

  In a series of 170 specimens, the ophthalmic artery arose from the internal carotid in 164 cases. In four cases it arose from the internal carotid and middle meningeal artery through an enlargement of the normal anastomosis between the orbital branch of the middle meningeal and recurrent meningeal branch of the lacrimal branch. This artery occasionally arises from the posterior communicating artery (circle of Willis), or from the middle cerebral when the internal carotid is absent. The middle meningeal artery may arise from the ophthalmic instead of from the maxillary artery.

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• Encyclopedia entry9 August 2026

  Superficial Temporal Artery

  The superficial temporal occasionally gives rise to the maxillary above the zygomatic arch, or to a tympanic artery. It may be small, in which case, it is replaced by the posterior auricular. When enlarged, it may give rise to branches normally provided by the facial such as the lateral nasal and superior and inferior labial. Its transverse facial branch is sometimes doubled. The anterior temporal branch of the superficial temporal is occasionally larger than the posterior branch, and may take the place of a defective facial artery.

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• Encyclopedia entry9 August 2026

  Sternocleidomastoid Artery

  This artery may arise directly from the external carotid (Livini, 42%; Poynter, 37%). When absent, this artery may be replaced by branches from the occipital, parotid, posterior auricular, lingual, or suprascapular.

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• Encyclopedia entry9 August 2026

  Maxillary Artery

  The origin of this artery is usually constant, but very rarely it is a branch of the facial artery. It has been seen, after leaving the temporal artery below the angle of the jaw, to pierce the medial pterygoid muscle in its upward course into the zygomatic fossa. Quain reported a case where the maxillary artery provided two vessels that entered the cranial cavity (one branch through the foramen rotundum and the second through the foramen ovale) to compensate for the absence of the internal carotid. The maxillary artery itself may also be doubled.

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