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Subclavian artery
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==Structure== From its origin, the subclavian artery travels laterally, passing between anterior and middle [[scalene muscles]], with the [[anterior scalene]] on its anterior side and the [[middle scalene]] on its posterior. This is in contrast to the [[subclavian vein]], which travels anterior to the anterior scalene. As the subclavian artery crosses the lateral border of the [[Rib cage|first rib]], it becomes the [[axillary artery]].<ref name="Vascular and Interventional Radiology-2006" /><ref name="Crystal-2019">{{Citation|last1=Crystal|first1=George J.|title=24 - Cardiovascular Physiology: Integrative Function|date=2019-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323481106000247|work=Pharmacology and Physiology for Anesthesia (Second Edition)|pages=473β519|editor-last=Hemmings|editor-first=Hugh C.|place=Philadelphia|publisher=Elsevier|language=en|doi=10.1016/b978-0-323-48110-6.00024-7|isbn=978-0-323-48110-6|access-date=2021-01-05|last2=Assaad|first2=Sherif I.|last3=Heerdt|first3=Paul M.|s2cid=87519432|editor2-last=Egan|editor2-first=Talmage D.|url-access=subscription}}</ref> On the right side, the subclavian artery arises from the brachiocephalic (innominate) artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta.<ref name="Vascular and Interventional Radiology-2006" /><ref name="Imaging Anatomy: Ultrasound (Second Edition)-2018" /> The two vessels, therefore, in the first part of their course, differ in length, direction, and relation with neighboring structures.<ref name="Barral-2011">{{Citation|last1=Barral|first1=Jean-Pierre|title=11 - The subclavian arteries|date=2011-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780702043512000119|work=Visceral Vascular Manipulations|pages=110β116|editor-last=Barral|editor-first=Jean-Pierre|place=Oxford|publisher=Churchill Livingstone|language=en|doi=10.1016/b978-0-7020-4351-2.00011-9|isbn=978-0-7020-4351-2|access-date=2021-01-05|last2=Croibier|first2=Alain|editor2-last=Croibier|editor2-first=Alain|url-access=subscription}}</ref> The left subclavian artery is around 9 [[Centimetre|cm]] long in [[adult]]s, while the right subclavian artery is around 6 cm long.<ref name="Barral-2011" /> Both have a width of 9-12 [[Millimetre|mm]].<ref name="Barral-2011" /> === Parts === In order to facilitate the description, each subclavian artery is divided into three parts: * The first part, also known as the prescalene part,<ref name="Barral-2011" /> extends from the origin of the vessel to the medial border of the scalenus anterior muscle.<ref name="Vascular and Interventional Radiology-2006">{{Citation|title=CHAPTER 7 - Upper Extremity Arteries|date=2006-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780721606217500123|work=Vascular and Interventional Radiology (Second Edition)|pages=182β203|editor-last=Valji|editor-first=Karim|place=Philadelphia|publisher=W.B. Saunders|doi=10.1016/B978-0-7216-0621-7.50012-3|language=en|isbn=978-0-7216-0621-7|access-date=2021-01-05|url-access=subscription}}</ref> * The second part, also known as the scalene part,<ref name="Barral-2011" /> lies behind the anterior scalene muscle.<ref name="Vascular and Interventional Radiology-2006" /> * The third part, also known as the postscalene part,<ref name="Barral-2011" /> extends from the lateral margin of the muscle to the outer border of the first rib, where it becomes the axillary artery.<ref name="Vascular and Interventional Radiology-2006" /><ref name="Crystal-2019" /> The first portions of the two vessels require separate descriptions; the second and third parts of the two arteries are practically alike. ====First part==== =====Right subclavian artery===== The first part of the right subclavian artery arises from the brachiocephalic trunk, behind the upper part of the right sternoclavicular articulation.<ref name="Vascular and Interventional Radiology-2006" /><ref name="Imaging Anatomy: Ultrasound (Second Edition)-2018">{{Citation|title=Lower Cervical Level and Supraclavicular Fossa|date=2018-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323548007500192|work=Imaging Anatomy: Ultrasound (Second Edition)|pages=124β129|editor-last=Woodward|editor-first=Paula J.|publisher=Elsevier|language=en|doi=10.1016/b978-0-323-54800-7.50019-2|isbn=978-0-323-54800-7|access-date=2021-01-05|editor2-last=Griffith|editor2-first=James F.|editor3-last=Antonio|editor3-first=Gregory E.|editor4-last=Ahuja|editor4-first=Anil T.|url-access=subscription}}</ref> It passes upward and lateralward to the medial margin of the [[scalenus anterior muscle]]. It ascends a little above the medial part of the [[clavicle]].<ref name="Barral-2011" /> It is covered, in front, by the integument, superficial fascia, the [[platysma muscle]], deep [[fascia]], the clavicular origin of the [[sternocleidomastoid muscle]], the [[sternohyoid muscle]], and the [[sternothyroid muscle]], and another layer of the [[deep fascia]]. It is crossed by the [[internal jugular vein]] and the [[vertebral vein]], by the [[vagus nerve]] and the cardiac branches of the vagus and sympathetic, and by the subclavian loop of the [[sympathetic trunk]] which forms a ring around the vessel. The [[anterior jugular vein]] is directed laterally in front of the artery, but is separated from it by the sternohyoid muscle and the sternothyroid muscle. Below and behind the artery is the [[pleura]], which separates it from the apex of the [[lung]].<ref name="Barral-2011" /> Behind the artery is the sympathetic trunk, the [[longus colli muscle]] and the first [[thoracic vertebra]] (T1). The [[Recurrent laryngeal nerve|right recurrent laryngeal nerve]] winds around the lower and back part of the vessel.<ref name="Barral-2011" /> =====Left subclavian artery===== The first part of the left subclavian artery arises from the [[aortic arch]], behind the [[Common carotid artery|left common carotid artery]], and at the level of the [[Thoracic vertebrae|fourth thoracic vertebra]].<ref name="Vascular and Interventional Radiology-2006" /><ref name="Imaging Anatomy: Ultrasound (Second Edition)-2018" /> It ascends in the [[Mediastinum|superior mediastinal cavity]] to the root of the neck, and then arches lateralward to the medial border of the scalenus anterior muscle. It is in relation, in front, with the [[vagus nerve]], the cardiac nerves, and the [[Phrenic nerve|phrenic nerves]], which lie parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein. It is covered by the sternothyroid muscle, the sternohyoid muscle, and the sternocleidomastoid muscle. Behind, it is in relation with the [[esophagus]], [[thoracic duct]], left recurrent laryngeal nerve, inferior cervical ganglion of the sympathetic trunk, and the longus colli muscle; higher up, however, the esophagus and thoracic duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and [[Internal jugular vein|internal jugular veins]]. Medial to it are the esophagus, [[trachea]], thoracic duct, and left recurrent laryngeal nerve. Lateral to it are the left pleura and lung.<ref name="Barral-2011" /> ====Second part==== The second portion of the subclavian artery lies behind the scalenus anterior muscle and in front of the [[Scalene muscles|scalenus medius muscle]].<ref name="Imaging Anatomy: Ultrasound (Second Edition)-2018" /><ref name="Barral-2011" /> It is very short, and forms the highest part of the arch described by the vessel. In front, it is covered by the skin, the superficial fascia, the platysma muscle, the deep cervical fascia, the sternocleidomastoid muscle, and the scalenus anterior muscle. On the right side of the neck, the [[phrenic nerve]] is separated from the second part of the artery by the scalenus anterior muscle, while on the left side it crosses the first part of the artery close to the medial edge of the muscle. Behind the artery are the pleura and the scalenus medius muscle. Above the artery is the [[brachial plexus]].<ref name="Barral-2011" /> Below the artery is the pleura.<ref name="Barral-2011" /> The subclavian vein lies below and anterior to the artery, separated from it by the scalenus anterior muscle.<ref name="Barral-2011" /> ====Third part==== The third portion of the subclavian artery runs downward and lateralward from the lateral margin of the scalenus anterior muscle to the outer border of the first rib, where it becomes the axillary artery.<ref name="Vascular and Interventional Radiology-2006" /><ref name="Crystal-2019" /> This is the most superficial portion of the vessel, and is contained in the subclavian triangle. It is covered, in front, by the skin, the superficial fascia, the platysma muscle, the supraclavicular nerves, and the deep cervical fascia.<ref name="Barral-2011" /> The external jugular vein crosses its medial part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which frequently form a plexus in front of the artery. Behind the veins, the nerve to the Subclavius descends in front of the artery. The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels. The subclavian vein is in front of and at a slightly lower level than the artery. Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the scalenus medius muscle. Above and to its lateral side are the upper trunks of the brachial plexus and the omohyoid muscle. Below, it rests on the upper surface of the first rib. ===Branches=== The subclavian arteries give off five major arteries each: the [[vertebral artery]], the [[internal thoracic artery]], the [[thyrocervical trunk]], the [[costocervical trunk]], and the [[dorsal scapular artery]].<ref name="Vascular and Interventional Radiology-2006" /><ref name="Barral-2011" />[[File:Subclavius 1st part.png|thumb|right|250px|Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. Branch of [[vertebral artery]] and [[thyrocervical]] trunk is labeled. Internal thoracic artery branches from same segment, but inferiorily, and is therefore not visible.]] {| class="wikitable" |- ! Part ! Branches ! Course |- | rowspan=3 |'''First part''' From its origin to the medial border of [[scalenus anterior]] | [[Vertebral artery]] | Runs cranially in the [[transverse foramen|transverse foramina]] of the [[cervical vertebrae]],<ref name="Vascular and Interventional Radiology-2006" /> joins the vertebral artery on the contralateral side, forming the [[basilar artery]] and joins the [[circle of Willis]]. |- | [[Internal thoracic artery]] | Runs caudally behind the ribs, giving off [[anterior intercostal branches]], perforating vessels to the [[breast]] and terminating in the [[superior epigastric artery]] and the [[musculophrenic artery]].<ref name="Vascular and Interventional Radiology-2006" /> |- | [[Thyrocervical trunk]] | Very short. Divides into [[inferior thyroid artery]], [[suprascapular artery]] and [[transverse cervical artery]] (''also called cervicodorsal trunk'').<ref name="Vascular and Interventional Radiology-2006" /> |- | '''Second part''' Lying behind scalenus anterior | [[Costocervical trunk]] | Splits into [[superior intercostal artery]] and [[deep cervical artery]].<ref name="Vascular and Interventional Radiology-2006" /> |- | '''Third part''' Between the lateral border of scalenus anterior and the outer border of the [[first rib]] | [[Dorsal scapular artery]] | From either second or third part.<ref name="Vascular and Interventional Radiology-2006" /> Passes backwards to supply [[levator scapulae]] and rhomboids. |} ===Development=== [[embryology|Embryologically]], the left subclavian simply arises from the left 7th [[intersegmental artery]],<ref>{{cite web|title=Aortic arches|url=http://www.embryology.ch/anglais/pcardio/arterien01.html|website=www.embryology.ch|access-date=12 July 2016}}</ref> while the right subclavian arises, proximal to distal: # right 4th [[aortic arches|aortic arch]] # right [[dorsal aorta]] # right 7th intersegmental artery Essentially, the 4th aortic arch and dorsal aorta form the aortic arch on the left, but since the right dorsal aorta regresses distal to the right 7th intersegmental artery, on the right they form the proximal portion of the subclavian artery. Since the left subclavian is then a tributary of the left common carotid, they can be thought of as arising from the brachiocephalic trunk. ===Variation=== The subclavian arteries vary in their origin, their course, and the height to which they rise in the neck. The origin of the right subclavian from the innominate takes place, in some cases, above the sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery may arise as a separate trunk from the arch of the aorta, and in such cases it may be either the first, second, third, or even the last branch derived from that vessel; in the majority, however, it is the first or last, rarely the second or third. When it is the first branch, it occupies the ordinary position of the innominate artery; when the second or third, it gains its usual position by passing behind the right carotid; and when the last branch, it arises from the left extremity of the arch, and passes obliquely toward the right side, usually behind the trachea, esophagus, and right carotid, sometimes between the esophagus and trachea, to the upper border of the first rib, whence it follows its ordinary course. In very rare instances, this vessel arises from the thoracic aorta, as low down as the fourth thoracic vertebra. Occasionally, it perforates the anterior scalene; more rarely it passes in front of that muscle. Sometimes the subclavian vein passes with the artery behind the Scalenus anterior. The artery may ascend as high as 4 cm. above the clavicle, or any intermediate point between this and the upper border of the bone, the right subclavian usually ascending higher than the left. The left subclavian is occasionally joined at its origin with the left common carotid artery, forming a left brachiocephalic trunk. The left subclavian artery is more deeply placed than the right in the first part of its course, and, as a rule, does not reach quite as high a level in the neck. The posterior border of the sternocleidomastoid corresponds pretty closely to the lateral border of the anterior scalene, so that the third portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the sternocleidomastoid. Some authors describe the subclavian artery as arising from the 7th intersegmental artery.
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