Vascular Anatomy of the Upper Extremity



Vascular Anatomy of the Upper Extremity


Amber Jones and Monica Smith Pearl


In this chapter, the classic arterial and venous anatomy of the upper extremity will be presented. Congenital variants will be discussed, as well as clinical correlates. It should be noted that fuller descriptions can be found in standard anatomy texts.



Vascular Imaging of the Upper Extremity


Imaging of the arterial and venous systems is an important component of the evaluation in many vascular disorders involving the upper extremity. In combination with clinical and laboratory observations, imaging provides crucial information for both diagnosis and management of these complex processes. This section will provide a brief overview of vascular imaging, including ultrasonography (US), computed tomographic angiography (CTA), magnetic resonance angiography (MRA), and conventional angiography. For a complete discussion of vascular imaging techniques, please see Chapters 2 and 3.


Real-time grayscale and color Doppler US is a useful, rapid, and portable imaging modality used to evaluate both the arterial and venous systems of the upper extremity. Arterial interrogation may be performed to assess for suspected limb ischemia, arterial stenosis, or patency of a hemodialysis arteriovenous fistula or graft. Assessment of the integrity of the venous side of the dialysis graft or fistula is also important, as is evaluation of thrombosis or compression of upper extremity veins. US can investigate flow hemodynamics along with vessel lumen and wall morphology. It is, however, operator dependent, does not fully evaluate upper extremity arterial inflow and central thoracic venous anatomy, and is limited in spatial display.1


CTA is a widely available technique that may be performed on all existing multidetector CT (MDCT) scanners (4 through 320 channels) to assess upper extremity vasculature. An excellent review on state-of-the-art techniques and clinical applications of CTA in the upper extremity by Hellinger et al. proposes four upper extremity CTA protocols: Aortic Arch with Upper Extremity Runoff, Upper Extremity Runoff, Upper Extremity Indirect CT Venography (CTV), and Upper Extremity Direct CTV based upon different clinical indications.1 This review highlights the various clinical scenarios in which CTA is useful and provides the technical parameters for acquisition, which are beyond the scope of this chapter.


Contrast-enhanced MRA is a rapid noninvasive imaging technique that aids in treatment planning and preoperative mapping of various vascular disorders of the upper extremity.2 It evaluates vascular integrity and patency, which may be compromised in cases of trauma, atherosclerosis, vasculitis, and malignancy. MRA not only defines the site, degree, and extent of stenosis or occlusion but also demonstrates collateral pathways in these processes. Advantages of contrast-enhanced MRA in the upper extremity include its noninvasive nature, lack of flow artifact, multiangular projection capability, and ability to delineate the small vessels of the hand. Limitations of this imaging technique in the upper extremity include limited coverage of 40 to 50 cm, variable circulation time among individuals, and overlapping of the arteries and veins in the hand.2 Other considerations include the effects of partial volume averaging and susceptibility artifacts, which may lead to an overestimation of stenosis in small blood vessels.


Conventional angiography is the gold standard for vascular imaging of the upper extremity, but it is an invasive procedure and is currently reserved for situations in which clinical questions remain despite information provided by the above-described noninvasive imaging modalities. It may also be used as the primary diagnostic modality when direct hemodynamic analysis is required for treatment planning or when there is intent to perform endovascular intervention in one combined procedure.1



Arterial Anatomy of the Upper Extremity


Subclavian Artery


The arterial blood supply of the upper extremity originates with the subclavian artery, whose typical diameter is 8 to 10 mm. The right subclavian artery arises from the brachiocephalic trunk, whereas the left subclavian artery is a direct branch from the aortic arch (Fig. 30-1). From its origin to the lateral border of the first rib, the subclavian artery supplies blood to the upper part of the chest, arms, and central nervous system (via the vertebral artery). The subclavian artery is divided into three segments based on its medial, posterior, or lateral relationship to the anterior scalene muscle. The first segments of the right and left subclavian arteries differ, whereas the second and third are nearly identical bilaterally. The first segment of the right subclavian artery begins at its origin from the brachiocephalic (innominate) trunk posterior to the upper border of the right sternoclavicular joint. It arches superolaterally, passes anterior to the extension of the pleural cavity in the root of the neck, and extends to the medial margin of the right anterior scalene muscle. It ascends variably 2 to 4 cm above the clavicle. The first segment of the left subclavian artery begins as a direct branch of the aortic arch after the origin of the left common carotid artery at the level of the third and fourth thoracic intervertebral disk spaces. It also ascends into the neck and arches laterally to the medial border of the left anterior scalene muscle. The second segment of the subclavian artery is posterior to the anterior scalene muscle. It is short and the most superior part of the vessel. The third segment descends from the lateral margin of the anterior scalene muscle and extends to the lateral border of the first rib, where it becomes the axillary artery. This portion is the most superficial part of the artery and lies partly in the supraclavicular triangle, the lower and smaller subdivision of the posterior cervical triangle.



The posterior cervical triangle of the neck is located in the lateral aspect of the neck in direct continuity with the upper limb. It is bordered anteriorly by the posterior edge of the sternocleidomastoid muscle, posteriorly by the anterior edge of the trapezius muscle, and inferiorly by the middle third of the clavicle. Its apex is the occipital bone, just posterior to the mastoid process where attachments of the trapezius and sternocleidomastoid converge. About 2.5 cm above the clavicle, it is crossed by the inferior belly of the omohyoid muscle, which divides the posterior triangle into the occipital and supraclavicular triangles.


All major nerves that innervate the upper limb originate from the brachial plexus, a somatic plexus that begins in the neck and passes laterally and inferiorly over the first rib into the axilla. Medially to laterally, it is composed of roots, trunks, divisions, and cords. The roots are formed by the anterior rami of C5 to C8 and most of T1. The roots and trunks enter the posterior triangle of the neck by passing between the anterior and middle scalene muscles and lie superior and posterior to the subclavian artery. The proximal parts of the brachial plexus are posterior to the subclavian artery in the neck, whereas more distal regions of the plexus surround the axillary artery (Fig. 30-2).



Variations in subclavian arterial anatomy are related to its origin and pathway. The right subclavian artery may arise above or below the sternoclavicular level as a distinct aortic arch branch, either the first or the last. When it arises as the first branch, it is in the position of a brachiocephalic trunk, as in the “classic” anatomy. If it arises as the last branch off the aortic arch, it ascends obliquely to the right and courses behind the trachea, esophagus, and right common carotid artery; alternatively in this scenario, it may pass between the trachea and esophagus. Occasionally, the left subclavian artery is combined at its origin with the left common carotid artery. Other variations in the pathway of the subclavian artery have also been described in relation to the anterior scalene muscle: perforating the muscle or, very rarely, passing anterior to it. Most of the branches of the subclavian artery arise from the artery’s first segment. Its branches include the vertebral artery, thyrocervical trunk, internal thoracic artery, and costocervical trunk (Fig. 30-3). These branches all arise from the first segment of the subclavian artery on the left. On the right, the costocervical trunk usually originates from the second segment of the subclavian artery. Additionally, on either side the dorsal scapular artery may arise from the third or, less often, the second segment of the subclavian artery or continue as the deep branch of the transverse cervical artery, a branch of the thyrocervical trunk.




Vertebral Artery


In more than 80% of cases, the vertebral artery originates from the superoposterior aspect of the first segment of the subclavian artery as its most proximal and largest branch. The vertebral artery ascends and enters the transverse foramen of the sixth cervical vertebra and continues superiorly through the foramina of the fifth through first cervical vertebrae. At the superior border of the first cervical vertebra, the artery curves medially, crosses the posterior arch of the first cervical vertebra, and passes through the foramen magnum to enter the posterior cranial fossa. Size of the vertebral arteries is variable, but a left-dominant artery is more common.


Variations involving the vertebral artery are related to its origin, usually a more proximal one. The left vertebral artery originates from the aortic arch between the left common carotid and the left subclavian artery in up to 5.8% of cases (Fig. 30-4). Its entrance into the cervical transverse foramen is also variable, but it most commonly enters at the level of the fifth cervical vertebra. Other rare variations involving the left vertebral artery that have been described include an origin from the aortic arch distal to the left subclavian artery, an origin from the left common carotid artery, or an origin from the external carotid artery. In less than 1% of cases, the right vertebral artery originates from the right common carotid artery or the aortic arch.




Thyrocervical Trunk


The thyrocervical trunk is the second branch of the subclavian artery, and it arises just distal to the vertebral artery from the superior surface of the first segment of the subclavian artery. Near the medial border of the anterior scalene muscle, the thyrocervical trunk classically divides into the inferior thyroid, transverse cervical, and suprascapular arteries. Only slightly more than 50% of individuals have this classic anatomy. Independent origins of one or more of these vessels from the subclavian artery are common.


The inferior thyroid artery is the superior continuation of the thyrocervical trunk. It ascends anterior to the anterior scalene muscle and turns medially just below the sixth cervical transverse process. Here it passes anterior to the vertebral vessels and posterior to the carotid sheath and its contents. It finally descends on the longus colli muscle to the inferior pole of the lateral lobe of the thyroid gland.


Branches of the inferior thyroid artery include muscular branches supplying the infrahyoid muscles, longus colli muscle, anterior scalene muscle, and the inferior pharyngeal constrictor, as well as pharyngeal branches supplying the lower pharynx, thyroid, and parathyroid glands. An important muscular branch is the ascending cervical artery, which arises as the inferior thyroid artery turns medially behind the carotid sheath; it ascends on the anterior surface of the prevertebral muscles, which it supplies, and sends branches to the spinal cord.


The middle branch of the thyrocervical trunk is the transverse cervical artery. This branch passes laterally and slightly posteriorly, anterior to the brachial plexus and the anterior scalene muscle, and enters and crosses the base of the posterior triangle. As it reaches the deep surface of the trapezius muscle, it divides into superficial and deep branches. The superficial branch continues on the deep surface of the trapezius muscle, and the deep branch continues on the deep surface of the rhomboid muscles near the medial border of the scapula. Alternatively, these branches may not arise in common as a transverse cervical artery. The superficial branch frequently arises directly from the thyrocervical trunk as a superficial cervical artery, and the deep branch may arise from the third or, less commonly, from the second part of the subclavian artery as the dorsal scapular artery.


The most inferior branch of the thyrocervical trunk is the suprascapular artery. It descends laterally and crosses anterior to the anterior scalene muscle, phrenic nerve, third part of the subclavian artery, and trunks of the brachial plexus. It reaches the superior scapular border, passes above the superior transverse scapular ligament, which separates it from the suprascapular nerve, and enters the supraspinatus fossa. In addition to supplying the supraspinatus and infraspinatus muscles, the suprascapular artery contributes branches to numerous structures along its course. Other alternative origins of the suprascapular artery include a direct origin from the third part of the subclavian artery or as a branch of the internal thoracic artery.



Internal Thoracic Artery


The internal thoracic artery arises from the anteroinferior aspect of the first part of the subclavian artery, directly below the origin of the thyrocervical trunk. It courses anteromedially behind the clavicle and the internal jugular and brachiocephalic veins. It descends behind the first six costal cartilages about 1 cm from the lateral sternal border, divides into numerous intermediate branches, and terminates in the musculophrenic and superior epigastric arteries at the level of the sixth intercostal space.


In the event of thoracic or abdominal aortic obstruction, the internal thoracic arteries are important potential sources of collateral blood supply via anterior anastomoses with the intercostal arteries and inferior epigastric arteries, respectively. Additionally, the internal thoracic arteries may provide collateral blood supply to the bronchial arteries.



Costocervical Trunk


The final branch of the subclavian artery in the root of the neck is the costocervical trunk. Depending on the side, it arises in a slightly different position. On the left it arises from the first segment of the subclavian artery, whereas on the right it arises from the second segment. On both sides it arches back above the cervical pleura to the neck of the first rib, where it divides into the deep cervical and supreme intercostal branches. The deep cervical artery anastomoses with the descending branch of the occipital artery and branches of the vertebral artery. In most cases the deep cervical artery arises from the costocervical trunk, but on occasion it may be a separate branch of the subclavian artery. The supreme intercostal artery descends anterior to the first rib and divides to form the posterior intercostal arteries for the first two intercostal spaces.


Clinically relevant scenarios related to stenosis or occlusion of the origin of the subclavian artery involve the potential collateral blood supply, including all the branches of the subclavian and axillary arteries. Subclavian steal, which may be associated with arm pain or central neurologic symptoms, is caused by retrograde flow in the ipsilateral vertebral artery. Additionally, steal physiology may affect other vessels in the upper extremity. For example, reversal of flow can occur in smaller subclavian artery branches such as the thyrocervical trunk and the internal mammary artery. In patients who undergo cardiac bypass surgery based on an internal mammary artery, proximal subclavian stenosis can cause a steal phenomenon involving the internal mammary artery that results in angina.


The axilla is the transition zone between the neck and arm, through which all major structures pass into and out of the upper limb. It is formed by the clavicle, scapula, upper thoracic wall, humerus, and related muscles.



Axillary Artery


The axillary artery, as a continuation of the subclavian artery, begins at the lateral margin of the first rib and ends normally at the inferior border of the teres major, where it becomes the brachial artery. The axillary artery supplies the walls of the axilla and related regions and continues as the major blood supply to more distal parts of the upper limb. Similar to the division of the subclavian artery based on its relationship to the anterior scalene muscle, the axillary artery is also divided into three segments based on its relationship to the pectoralis minor muscle: proximal, posterior, and distal.

Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Vascular Anatomy of the Upper Extremity
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