Vasculature of the Thorax

Overview
The blood vessels of the thorax play a crucial role in supplying thoracic organs and forming a key passageway between the pulmonary and systemic circulations. This section provides an introduction to the principal arterial and venous channels found within the chest.

Key Structures
Subjects covered include the aorta, with emphasis on its anatomical course and major branches, as well as the superior vena cava, focusing on its formation, route, and contributing veins.

Clinical Relevance and Learning Focus
A sound understanding of thoracic vascular anatomy is essential for analysing mediastinal imaging, identifying acute vascular conditions, and evaluating disorders such as aneurysms, vascular obstruction, and venous congestion.

The Superior Vena Cava

Contents

• Anatomical Position
• Jugular Venous Pressure
• Tributaries
• Superior Vena Cava Obstruction

The superior vena cava (SVC) is a large vein without valves that transports deoxygenated blood from the upper part of the body back to the right atrium of the heart.

This article describes the anatomy of the superior vena cava, including its location, venous inflow, and clinical importance.

Anatomical Position

The superior vena cava is a major vein, measuring up to around 2 cm in diameter and approximately 7 cm in length.

It is formed by the confluence of the left and right brachiocephalic veins, just behind the first right costal cartilage. From this point, it descends vertically through the superior mediastinum, positioned posterior to the intercostal spaces and lying to the right of both the aorta and the trachea.

At the level of the second costal cartilage, the SVC passes into the middle mediastinum, where it becomes enclosed by the fibrous pericardium. It ends by draining into the upper portion of the right atrium, opposite the third costal cartilage.

Clinical Relevance

Jugular Venous Pressure

Because the superior vena cava lacks valves, pressure changes within the right atrium are transmitted directly into the right internal jugular vein.

Observation of the right internal jugular vein therefore provides an estimate of the jugular venous pressure (JVP), which reflects right atrial pressure. To assess the JVP, the patient is positioned at a 45° incline with the head gently turned to the left. The venous pulsation is observed between the two heads of the sternocleidomastoid muscle.

An elevated JVP may be seen in conditions such as right-sided heart failure, pulmonary hypertension, or obstruction of the superior vena cava.

Tributaries

The superior vena cava carries venous blood from the head and neck, both upper limbs, and parts of the thorax.

It is formed by the joining of the right and left brachiocephalic veins, which drain blood from the head, neck, and upper limbs. At approximately the level of the T4 vertebra, the azygos vein joins the SVC, returning blood from the thoracic wall and upper lumbar region.

Additional smaller tributaries draining into the SVC include:

• Mediastinal veins
• Oesophageal veins
• Pericardial veins

Clinical Relevance

Superior Vena Cava Obstruction

The superior vena cava has thin walls and operates under low pressure, making it susceptible to compression.

Obstruction of the SVC may result from external compression or from blockage within the vessel itself. The most frequent cause is malignancy, particularly lung cancer, lymphoma, or metastatic disease.

When venous return through the SVC is impaired, blood backs up into the veins of the upper body, leading to swelling of the face, neck, and upper limbs. Symptoms often include breathlessness and visibly distended superficial veins.

One clinical method used to assess SVC obstruction is Pemberton’s test. The patient is asked to raise both arms above the head; the test is considered positive if facial swelling or cyanosis develops after about one minute.