Syntopy and morphometry
The subclavian artery is projected onto the skin of the neck along a line running from the middle of the upper border of the clavicle to the angle between the clavicle and the sternal head of the sternocleidomastoid muscle (the sternoclavicular joint area).
In its initial segment, the vessel has a complex syntopy:
- Anteriorly, the venous angle (Pirogov's angle) is projected onto the artery.
- Medially, the vagus nerve passes along it.
- Laterally, the phrenic nerve descends.
- On the right, the artery borders the brachiocephalic trunk, and on the left, the common carotid artery.
The dimensions of the arteries on the right and left differ. The length of the right a. subclavia ranges from 7 to 13 cm. There is an inverse relationship: the longer the brachiocephalic trunk, the shorter the right subclavian artery. The left artery is longer than the right by approximately 4 cm due to the additional thoracic segment.
Division into parts
Topographically, the subclavian artery is conventionally divided into four parts, based on its relation to the anterior scalene muscle and the clavicle:
- First part: extends from the origin to the inner border of the anterior scalene muscle. It includes both intrathoracic and extrathoracic segments. Here, the vessel lies on the cupula of the pleura and is firmly attached to it by connective tissue cords.
- Second part: is located in the interscalene triangle (spatium interscalenum). The artery passes between the anterior and middle scalene muscles, resting on the 1st rib.
- Third part (supraclavicular part): runs from the outer border of the anterior scalene muscle to the clavicle.
- Fourth part: continues from the clavicle to the upper border of the pectoralis minor muscle. This segment is often referred to as the axillary artery and is studied within the clavipectoral triangle (trigonum clavipectorale).
Interestingly, the length of the second, third, and fourth parts is the same on both sides, measuring 5–7 cm.
Key branches
Most of the major branches arise from the first part of the artery, before it enters the interscalene triangle:
- Vertebral artery (a. vertebralis): originates 1.0–1.5 cm medial to the anterior scalene muscle. It ascends to the transverse process of the 6th cervical vertebra and continues upward within the osseous canal. Between the 1st and 2nd vertebrae, it forms a bend (siphon), enters the cranial cavity through the foramen magnum, and at the level of the lower border of the pons, joins the contralateral artery to form a single basilar artery (a. basilaris).
- Internal thoracic artery (a. thoracica interna): arises from the inferior circumference, lies on the cupula of the pleura (where it is covered by the subclavian vein), and descends onto the inner surface of the anterior chest wall.
- Thyrocervical trunk (truncus thyrocervicalis): a short trunk that arises just before the interscalene triangle and branches into 4 vessels (inferior thyroid, superficial cervical, ascending cervical, and suprascapular arteries).
- Costocervical trunk (truncus costocervicalis): in 50% of cases, it originates from the first part (between the vertebral artery and the thyrocervical trunk). It arches over the cupula of the pleura toward the spine.
- Transverse cervical artery (a. transversa colli): most frequently (50%) arises from the first part. Its most important topographical feature is that it pierces the brachial plexus, passing directly between its trunks.
Briefly: answers to topical questions
Where does the vertebral artery originate and where does it run?
The vertebral artery (a. vertebralis) originates from the first part of the subclavian artery and runs toward the brain.
It branches off 1.0–1.5 cm medial to the inner border of the anterior scalene muscle. The subsequent course of the artery:
- Enters the transverse foramen of the 6th cervical vertebra and ascends in the osseous canal.
- Forms a bend (siphon) between the 1st and 2nd vertebrae.
- Enters the cranial cavity through the foramen magnum (foramen magnum).
At the base of the brain (at the level of the pons), the right and left vertebral arteries fuse to form a single basilar artery (a. basilaris).
Which branches make up the thyrocervical trunk?
The thyrocervical trunk (truncus thyrocervicalis) typically gives rise to four branches:
- Inferior thyroid artery (a. thyroidea inferior) — ascends to the level of the 6th cervical vertebra, forms a loop (arch), and descends inferiorly and medially toward the lower third of the posterior surface of the lateral lobe of the thyroid gland.
- Superficial cervical artery (a. cervicalis superficialis) — crosses anteriorly the anterior scalene muscle, the levator scapulae muscle, and the supraclavicular part of the brachial plexus.
- Ascending cervical artery (a. cervicalis ascendens).
- Suprascapular artery (a. suprascapularis) — forms an arch with its convexity facing inferiorly and lies with the accompanying vein posterior to the upper border of the clavicle.
Class and exam questions
What is the main difference between the right and left subclavian arteries?
The right artery arises from the brachiocephalic trunk, and the left one directly from the aortic arch. Due to the presence of the thoracic segment, the left artery is approximately 4 cm longer than the right one.
Which branch of the subclavian artery passes through the brachial plexus?
Transverse cervical artery (a. transversa colli). It passes directly between the trunks of the brachial plexus, subsequently dividing into superficial and deep branches.
Where is the second part of the subclavian artery located?
It is located in the interscalene triangle (spatium interscalenum). The artery lies on the first rib between the anterior and middle scalene muscles.
What else to study on this topic
- Topography of the intracranial segment of the vertebral artery and formation of the basilar artery.
- Branches of the thyrocervical trunk: course of the superficial cervical and suprascapular arteries.
- Syntopy of the artery and the cupula of the pleura in the first segment.
- Anatomy of the branches of the costocervical trunk (highest intercostal and deep cervical arteries).
- Transition of the fourth part of the subclavian artery into the axillary artery.
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