Surgical Treatment of the Subclavian and Axillary Artery

Surgical Anatomy of the Subclavian and Axillary Artery

In most cases, the right subclavian artery branches from the brachiocephalic trunk and the left subclavian artery arises as the most distal branch of the aortic arch. Each artery emerges from the mediastinum and arches over the ipsilateral cervical pleura and pulmonary apex to pass between the clavicle and the first rib. In this trajectory the arteries pass behind the respective anterior scalene muscle and between the clavicle and the first rib. Before passing behind the anterior scalene muscle, each artery gives off three branches. The vertebral arteries originate first on the superoposterior aspect of each subclavian artery and ascend to enter the transverse foramina of C6. Next, the internal thoracic arteries originate on the inferior aspect of each subclavian artery and descend along the anterior chest wall behind the costal cartilages. The short thyrocervical trunk originates anteriorly as the third branch near the medial border of the anterior scalene muscle and quickly divides into three or four smaller branches. As the subclavian arteries pass behind the anterior scalene muscle, each gives off a costocervical branch on the posterior aspect and a dorsal scapular branch on the lateral aspect.

Key anatomic features in the thoracic outlet include the tightly packed neurovascular structures of the superior thoracic aperture and the proximity of the phrenic nerve, thoracic duct, and subclavian vein. The nerves of the brachial plexus emerge between the anterior and the middle scalene muscles, descend posterior to the subclavian artery, and enter the axillary passage close to the artery at the lateral border of the first rib. The phrenic nerve runs from lateral to medial as it descends on the surface of the anterior scalene muscle. It descends into the chest between the subclavian artery and the subclavian vein, just medial to the point where the anterior scalene muscle attaches to the scalene tubercle of the first rib. The subclavian vein enters the axillary passage behind the subclavius muscle, courses anterior to the anterior scalene muscle, and joins the internal jugular vein to enter the mediastinum as a single brachiocephalic vein. On the left side, the thoracic duct arches over the subclavian artery and terminates at the junction of the internal jugular and subclavian veins.

The axillary artery extends from the lateral border of the first rib to the lateral edge of the teres major muscle. The artery is divided anatomically into three parts by the pectoralis minor muscle. The first segment, medial to the muscle, has one branch: the supreme thoracic artery. The second segment, behind the muscle, has two branches: the thoracoacromial and lateral thoracic arteries. The third segment, lateral to the muscle, has three branches: the subscapular artery and the medial and lateral humeral circumflex arteries.

The divisions and cords of the brachial plexus interdigitate around the axillary artery and form a complex array that risks injury during axillary artery dissection. The cords of the brachial plexus assume their final configuration as nerves around the third segment of the axillary artery. The truncal origins of the median nerve cross anterior to the artery at this level and are particularly prone to injury during dissection in this area.

Anatomic Considerations in an Aberrant Right Subclavian Artery

An aberrant right subclavian artery arises as the fourth branch of the aortic arch in about 1% of the population, and the prevalence is higher in individuals with other cardiovascular anomalies, such as right-sided aortic arch. The aberrant artery most often tracks across the mediastinum posterior to the esophagus and right common carotid artery to reach the right arm ( Fig. 14-2 ). Less commonly, the artery may course between the esophagus and the trachea or anterior to the trachea. A number of anatomic anomalies associated with an aberrant right subclavian artery should be considered in operative planning :

• Esophageal compression. A small percentage of individuals with the anomaly develop symptoms associated with posterior compression of the esophagus (dysphagia lusoria) ( Fig. 14-3 ). The true incidence of dysphagia lusoria and the reasons underlying late development of symptoms remain unknown. In such patients transposition of the aberrant artery can be curative and definitive in the absence of the other considerations given here.

  

• Kommerell diverticulum . Approximately 60% of individuals who have an aberrant right subclavian artery have dilation at the aortic origin known as Kommerell diverticulum. This segment is prone to aneurysmal degeneration that may result in compression of surrounding structures or catastrophic rupture. Therefore the presence of Kommerell diverticulum is an indication for repair. Typically this requires a staged approach with initial transposition of the subclavian artery, followed by open or endovascular repair of the diverticulum.

• Nonrecurrent right laryngeal nerve. The associated anomaly of a nonrecurrent laryngeal nerve should always be considered in the patient with an aberrant right subclavian artery. Although a nonrecurrent laryngeal nerve has been reported on the left side, the anomaly is more common on the right. The nerve branches directly from the vagus nerve at the level of the carotid bifurcation and is at risk of injury during dissection of the carotid bulb, especially on the posterior or medial aspect. Fortunately, carotid exposure is not required at this level during modern operations to correct dysphagia lusoria (described later).

• Thoracic duct anomalies. A right-sided thoracic duct may arch over the aberrant right subclavian artery to join the confluence of the internal jugular and subclavian veins.

Avoiding Injuries to the Thoracic Duct

Chylous leak is a morbid complication of subclavian artery exposure. The complication is best avoided by meticulous ligation of lymphatics in the scalene fat pad and early identification of the thoracic duct during exposure of the left subclavian artery. The duct courses on the medial side of the fat pad and arches over the subclavian artery to reach the confluence of the subclavian and internal jugular veins. The duct should be carefully ligated and divided near its point of entry into the posterior vein wall. There may be multiple ducts that may enter the subclavian or internal jugular veins directly. A right-sided thoracic duct may be associated with an aberrant right subclavian artery.

Avoiding Injuries to the Brachial Plexus

Most brachial plexus injuries arise as a consequence of undue traction, especially during resection of cervical ribs. During exposure of the proximal subclavian artery, self-retaining retractors should be carefully placed in the posterior incision to avoid contact with nerve roots and trunks as they course downward from their cervical origins behind the anterior scalene muscle. In the lateral wound the nerve divisions descend to join the subclavian artery as it crosses under the clavicle; nerve injury can occur from misplaced arterial clamps in this area. Nerve injury can also occur during first rib resection if the nerves are not well identified and gently retracted from the cutting instrument. The nerves course over anomalous cervical ribs, and overzealous traction must be carefully avoided during rib excision.

Avoiding Injuries to the Vertebral Artery

The vertebral artery arises on the superoposterior aspect of the subclavian artery and may be at risk for injury from excessive traction or inadvertent entry during proximal exposure of the subclavian artery. To avoid these complications, the vertebral artery should be carefully identified during medial dissection. The vertebral artery can be identified in the center of the angle formed by the anterior scalene and longus coli muscles. It lies adjacent to the vertebral vein and sympathetic chain and is crossed by the inferior thyroid artery.

In patients with an aberrant right subclavian artery, the right vertebral artery is at risk of kinking as the aberrant subclavian artery is transposed anteriorly for anastomosis to the common carotid artery. This complication is avoided by ensuring that there is an adequate length of the subclavian artery that allows laxity as it is brought anteriorly to join the carotid artery.

Avoiding Injuries Behind the Clavicle

Although exposure of the subclavian vein is rarely necessary during arterial dissection, the proximity of the vein makes it prone to injury at three points. The first is near the clavicular head, where excessive traction on the confluence with the internal jugular vein may result in a tear that is difficult to control. The second is the point at which the clavicle crosses over the first rib: the vein is prone to injury during first rib resection and should therefore be carefully identified and protected during medial rib transection. The third point of potential injury is in the thoracic outlet as the vein crosses over the first rib. During arterial reconstruction, the tunnel between the supraclavicular and the infraclavicular incisions should be created under direct vision to avoid venous injury (described later).

Selection of a Conduit

Direct transposition and anastomosis of the subclavian artery onto the common carotid artery is associated with the highest 5-year patency and is preferred over free grafts whenever feasible. Direct transposition can usually be accomplished in patients with dysphagia lusoria (described later).

In patients who require repair of a subclavian artery aneurysm, short interposition grafts using prosthetic material such as ringed polytetrafluoroethylene represent a durable option after the aneurysm has been resected. Autogenous saphenous vein grafts have also been used in this position and have the theoretical advantage of resistance to infection. However, the prosthetic graft often carries the advantage of better size match, and external ring support helps prevent graft kinking in its position beneath the clavicle.

A prosthetic graft such as ringed polytetrafluoroethylene is associated with superior patency rates compared with the autogenous saphenous vein for carotid-subclavian bypass. The small caliber of the saphenous vein and the potential for kinking from neck mobility in multiple axes appear to limit its durability in this position.

The superficial femoral vein is a durable alternative to prosthetic grafts in this location and carries the advantages of resistance to infection and superior size match. This large graft also appears to resist kinking.