Superior Vena Cava Tributaries (Azygos, Hemiazygos, Brachiocephalic) - Anatomy

Summary

This video explores the anatomy of the superior vena cava and its associated veins, including the azygos, hemiazygos, accessory hemiazygos, and brachiocephalic veins. It explains their structure, tributaries, and functions in draining deoxygenated blood from the upper body to the heart. Special attention is given to the variations in vein lengths and tributaries, as well as their role in conditions like liver disease. The video provides a detailed yet accessible overview, helping viewers understand the complex venous systems and their anatomical relationships.

Takeaways

• 😀 The superior vena cava (SVC) is a short, wide vein that carries deoxygenated blood from the upper half of the body, including the head, neck, upper limbs, and thorax.
• 😀 The SVC empties into the right atrium of the heart at the level of the third sternocostal joint.
• 😀 The azygos vein, located on the right side of the vertebral column, drains blood from the right thoracic wall and certain abdominal structures.
• 😀 The azygos vein is unpaired and has no valves, which makes it significant in cases of portal hypertension, where it can act as a portocaval anastomosis.
• 😀 The hemiazygos vein, located on the left side, is similar to the azygos vein and drains the left posterior thoracic wall, emptying into the azygos vein at T8–T9.
• 😀 The accessory hemiazygos vein drains the 4th–7th left intercostal veins and can communicate with either the hemiazygos or azygos veins.
• 😀 The brachiocephalic veins are formed by the union of the subclavian and internal jugular veins, and they drain blood from the head, neck, and upper limbs.
• 😀 The right brachiocephalic vein is shorter (about 3 cm) than the left, which is longer (about 6 cm).
• 😀 The tributaries of the brachiocephalic veins include the vertebral veins, inferior thyroid veins, internal thoracic veins, and intercostal veins, with specific variations between the right and left sides.
• 😀 Clinical significance includes variations in venous drainage, as veins like the azygos and hemiazygos can compensate for blocked or narrowed veins, such as in liver disease or portal hypertension.

Q & A

What is the primary function of the superior vena cava?

The superior vena cava carries deoxygenated blood from the upper half of the body, including the head, neck, upper limbs, thorax, and upper part of the back, to the right atrium of the heart.

How does the azygos vein connect to the superior vena cava?

The azygos vein ascends along the right side of the vertebral column and arches anteriorly at the level of T4, emptying into the superior vena cava.

Why is the azygos vein called 'unpaired'?

The term 'azygos' comes from the Greek words 'a-' meaning 'not' and 'zygos' meaning 'paired', indicating that this vein is unpaired and located only on the right side of the vertebral column.

What is a key difference between the azygos vein and hemiazygos vein?

The azygos vein is located on the right side of the body, whereas the hemiazygos vein is on the left side. The hemiazygos vein drains into the azygos vein around the T8-T9 vertebrae.

What role do the azygos and hemiazygos veins play in portocaval and cavo-caval anastomoses?

The azygos and hemiazygos veins are valveless, which allows them to act as alternative pathways for blood if there is an obstruction, such as a narrowed portal vein due to liver disease.

What are the tributaries of the azygos vein?

The azygos vein has both visceral tributaries (such as the esophageal, bronchial, pericardial, and mediastinal veins) and parietal tributaries (including the right superior intercostal veins and right posterior intercostal veins).

What is the relationship between the accessory hemiazygos vein and the intercostal veins?

The accessory hemiazygos vein receives blood from the 4th to 7th left intercostal veins, and may connect with the left superior intercostal veins or the azygos vein, depending on individual variations.

What is the role of the left superior intercostal vein?

The left superior intercostal vein drains the upper 3–4 intercostal spaces on the left side and connects with the left brachiocephalic vein.

What distinguishes the right and left brachiocephalic veins?

The right brachiocephalic vein is about 3 cm long, while the left one is about 6 cm long. Both receive blood from similar tributaries, including the vertebral, internal thoracic, and inferior thyroid veins, but the left also drains additional veins like the left superior intercostal and thymic veins.

What tributaries drain into the right brachiocephalic vein?

The right brachiocephalic vein receives blood from the right vertebral vein, right inferior thyroid vein, right internal thoracic vein, right supreme intercostal vein, and several other tributaries draining the thoracic region.