Where Does Dorsal Scapular Artery Come From

The dorsal scapular artery, a vital blood vessel in the shoulder region, plays a crucial role in supplying oxygen and nutrients to several muscles essential for shoulder movement and stability. Understanding its origin, course, and distribution is paramount for medical professionals, particularly surgeons and radiologists, as well as students in anatomy and related fields. This article delves into the anatomical origins of the dorsal scapular artery, its variations, and its clinical significance.

Anatomical Origins of the Dorsal Scapular Artery

The origin of the dorsal scapular artery is somewhat variable, which is an important consideration in surgical planning and diagnostic imaging. Classically, it is described as arising from one of two main sources:

The Subclavian Artery: In the majority of individuals, the dorsal scapular artery originates directly from the subclavian artery. The subclavian artery is a major vessel that arises from the aortic arch on the left side of the body and from the brachiocephalic trunk on the right. It courses laterally, passing over the first rib, and continues into the axilla as the axillary artery. When the dorsal scapular artery arises from the subclavian artery, it typically emerges between the scalenus anterior and scalenus medius muscles.
The Transverse Cervical Artery: In a significant proportion of cases, the dorsal scapular artery arises as a branch of the transverse cervical artery. The transverse cervical artery itself is a branch of the thyrocervical trunk, which in turn originates from the subclavian artery. When the dorsal scapular artery arises from the transverse cervical artery, the transverse cervical artery is often referred to as the cervicodorsal artery. This variation is important because the cervicodorsal artery must then give off a superficial branch (the typical transverse cervical artery) to supply the trapezius muscle, and a deep branch (the dorsal scapular artery) that continues along the medial border of the scapula.

Detailed Course and Distribution

Regardless of its origin, the dorsal scapular artery follows a consistent course through the posterior triangle of the neck and along the medial border of the scapula:

Emergence and Initial Course: Whether arising directly from the subclavian artery or as a branch of the transverse cervical (cervicodorsal) artery, the dorsal scapular artery emerges in the lower part of the neck. It typically passes posteriorly through the brachial plexus and between the trunks or divisions of the plexus. This close proximity to the brachial plexus means that surgical procedures in this area carry a risk of injury to both the artery and the nerves.
Passage through or deep to the Scapular Muscles: As it descends towards the scapula, the dorsal scapular artery usually passes deep to the levator scapulae muscle. In some instances, it may pierce the levator scapulae. It continues its course deep to the rhomboid muscles (rhomboid minor and rhomboid major).
Supply to the Scapular Region: The dorsal scapular artery supplies blood to the following muscles:
- Levator Scapulae: This muscle elevates the scapula and assists in neck movements.
- Rhomboid Minor and Rhomboid Major: These muscles retract and rotate the scapula, helping to maintain its position against the thoracic wall.
- Trapezius: Although the trapezius is primarily supplied by the superficial branch of the transverse cervical artery (or the transverse cervical artery itself when the dorsal scapular artery arises from it), the dorsal scapular artery may contribute to its blood supply, particularly the lower portion of the muscle.
Anastomoses: The dorsal scapular artery participates in anastomoses (connections) with other arteries around the scapula, ensuring a collateral blood supply to the region. These anastomoses include connections with the suprascapular artery (a branch of the thyrocervical trunk) and the circumflex scapular artery (a branch of the subscapular artery from the axillary artery). These connections are crucial because if one artery is blocked or injured, the other arteries can provide sufficient blood flow to maintain tissue viability.

Variations in Origin and Course

The variations in the origin of the dorsal scapular artery are well-documented in anatomical studies and have significant clinical implications. Understanding these variations is crucial for surgeons performing procedures in the neck and shoulder region, as well as for radiologists interpreting imaging studies.

Incidence of Origins: Studies have reported varying frequencies of the dorsal scapular artery arising from the subclavian artery versus the transverse cervical artery. Generally, the dorsal scapular artery arises from the subclavian artery in approximately 30-60% of cases. In the remaining cases, it originates from the transverse cervical artery (as the cervicodorsal artery).
Clinical Significance of Variations: The variations in origin can affect the surgical approach during procedures such as lymph node dissection, brachial plexus exploration, or subclavian artery catheterization. If the surgeon is unaware of the variation, there is an increased risk of inadvertently injuring the dorsal scapular artery or its parent vessel, leading to bleeding or compromising the blood supply to the scapular muscles.
Imaging Considerations: Radiologists should be aware of these variations when interpreting angiograms or CT angiograms of the neck and shoulder. Misidentification of the dorsal scapular artery or its origin could lead to diagnostic errors or inappropriate interventions.

Embryological Development

To fully understand the variations in the origin of the dorsal scapular artery, it is helpful to consider its embryological development. During early development, the arterial system undergoes significant remodeling and reorganization. Several intersegmental arteries arise from the dorsal aorta and supply the developing body wall, including the upper limb.

Early Arterial Network: Initially, a network of intersegmental arteries supplies the developing upper limb and shoulder region. These arteries anastomose with each other to form longitudinal channels.
Regression and Persistence: As development progresses, some of these intersegmental arteries regress, while others persist and become the definitive arteries of the upper limb and shoulder. The subclavian artery and its branches, including the thyrocervical trunk and transverse cervical artery, are derived from this early arterial network.
Variations Explained by Embryology: The variations in the origin of the dorsal scapular artery can be explained by the differential persistence or regression of certain segments of the early arterial network. If the intersegmental artery that normally forms the dorsal scapular artery regresses, the artery may arise from a neighboring vessel, such as the transverse cervical artery.

Clinical Significance

The dorsal scapular artery is clinically significant for several reasons:

Surgical Considerations: As mentioned earlier, the variations in the origin and course of the dorsal scapular artery are important for surgeons performing procedures in the neck and shoulder region. Injury to the artery can lead to bleeding, hematoma formation, or compromise of the blood supply to the scapular muscles. This can result in postoperative pain, weakness, or impaired shoulder function.
Thoracic Outlet Syndrome (TOS): The dorsal scapular artery, along with the subclavian artery and brachial plexus, can be compressed in the thoracic outlet, the space between the clavicle and the first rib. This compression can lead to thoracic outlet syndrome, a condition characterized by pain, numbness, tingling, and weakness in the shoulder, arm, and hand. In some cases, compression of the dorsal scapular artery can cause ischemia (reduced blood flow) to the scapular muscles, contributing to the symptoms of TOS.
Scapular Winging: Injury to the dorsal scapular nerve (which often accompanies the dorsal scapular artery) or compromise of the dorsal scapular artery itself can lead to weakness or paralysis of the rhomboid muscles and levator scapulae. This can result in scapular winging, a condition in which the medial border of the scapula protrudes posteriorly from the thoracic wall. Scapular winging can cause pain, limited range of motion, and impaired shoulder function.
Myofascial Pain: The dorsal scapular artery and its surrounding muscles can be involved in myofascial pain syndrome. Trigger points in the levator scapulae and rhomboid muscles can refer pain to the neck, shoulder, and upper back. Palpation of the dorsal scapular artery may elicit tenderness in individuals with myofascial pain in this region.
Anatomical Landmark: The dorsal scapular artery can serve as an important anatomical landmark during surgical procedures. Its consistent relationship to the brachial plexus and the scapular muscles can help surgeons identify and protect these structures during dissection.

Diagnostic Imaging

Several imaging modalities can be used to visualize the dorsal scapular artery and assess its anatomy and pathology:

Conventional Angiography: This is an invasive procedure that involves injecting contrast dye into the subclavian artery or axillary artery and taking X-ray images to visualize the arteries. Conventional angiography is rarely used today due to the availability of less invasive techniques.
CT Angiography (CTA): This is a non-invasive imaging technique that uses computed tomography (CT) to visualize the arteries after intravenous injection of contrast dye. CTA can provide detailed images of the dorsal scapular artery, its origin, course, and relationship to surrounding structures. It is useful for evaluating variations in anatomy, as well as for detecting aneurysms, stenosis (narrowing), or other abnormalities of the artery.
MR Angiography (MRA): This is another non-invasive imaging technique that uses magnetic resonance imaging (MRI) to visualize the arteries. MRA can be performed with or without intravenous contrast dye. It provides good visualization of the dorsal scapular artery and its surrounding structures, and is particularly useful for evaluating soft tissue structures, such as the brachial plexus.
Ultrasound: Doppler ultrasound can be used to assess blood flow in the dorsal scapular artery. This technique is non-invasive and can be performed at the bedside. It is useful for detecting stenosis or occlusion of the artery, as well as for evaluating the effects of thoracic outlet syndrome on blood flow.

Surgical Considerations and Techniques

Surgical procedures involving the dorsal scapular artery require careful planning and execution to minimize the risk of injury.

Preoperative Planning: Before any surgical procedure in the neck or shoulder region, surgeons should carefully review the patient's imaging studies to identify any variations in the origin or course of the dorsal scapular artery. This information can help guide the surgical approach and minimize the risk of inadvertent injury to the artery.
Surgical Approach: The surgical approach should be tailored to the specific procedure and the patient's anatomy. In general, a meticulous dissection technique should be used to identify and protect the dorsal scapular artery and its surrounding structures.
Ligation and Reconstruction: If the dorsal scapular artery is injured during surgery, it may be necessary to ligate (tie off) the artery to control bleeding. In some cases, it may be possible to reconstruct the artery using microsurgical techniques. However, ligation of the dorsal scapular artery is usually well-tolerated, as the scapular muscles receive collateral blood supply from other arteries.
Nerve Preservation: As the dorsal scapular nerve often accompanies the dorsal scapular artery, surgeons should take care to protect this nerve during dissection. Injury to the dorsal scapular nerve can lead to weakness or paralysis of the rhomboid muscles and levator scapulae, resulting in scapular winging.

Frequently Asked Questions (FAQ)

What is the dorsal scapular artery? The dorsal scapular artery is a blood vessel that supplies oxygen and nutrients to several muscles in the shoulder region, including the levator scapulae, rhomboid minor, rhomboid major, and trapezius.
Where does the dorsal scapular artery originate? The dorsal scapular artery typically originates from either the subclavian artery or the transverse cervical artery (as the cervicodorsal artery).
Why is the origin of the dorsal scapular artery variable? The variations in origin are due to the complex embryological development of the arterial system in the upper limb and shoulder region.
What is the clinical significance of the dorsal scapular artery? The dorsal scapular artery is clinically significant because injury to the artery can lead to bleeding, hematoma formation, or compromise of the blood supply to the scapular muscles. It can also be involved in thoracic outlet syndrome and myofascial pain syndrome.
How is the dorsal scapular artery visualized on imaging studies? The dorsal scapular artery can be visualized using CT angiography (CTA), MR angiography (MRA), or Doppler ultrasound.

Conclusion

The dorsal scapular artery is a vital blood vessel in the shoulder region, supplying blood to several muscles essential for shoulder movement and stability. Understanding its anatomical origins, course, variations, and clinical significance is crucial for medical professionals involved in the diagnosis and treatment of conditions affecting the neck and shoulder. The variations in its origin, stemming from either the subclavian or transverse cervical artery, underscore the importance of detailed anatomical knowledge in surgical planning and radiological interpretation. Awareness of its potential involvement in conditions like thoracic outlet syndrome and its role as an anatomical landmark further highlights its clinical relevance. Through a comprehensive understanding of the dorsal scapular artery, clinicians can optimize patient care and minimize the risk of complications in surgical and diagnostic procedures.