The Anatomy of the Internal Jugular Vein

The internal jugular vein is the largest vein in the neck that serves as the main source of blood flow down from the head. Obstruction of blood flow through the internal jugular vein can cause backflow of blood into the brain, increasing intracranial pressure, which can cause serious brain damage if left untreated.

veins and arteries of the neck

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Anatomy

Veins carry deoxygenated blood from organs, muscles, and other structures back to the heart. They typically have a lower blood pressure than arteries.

While their walls are thinner, veins are usually larger in diameter than arteries and hold about 80% of the body’s total blood, whereas arteries typically only circulate 20% of the blood.

Structure

The walls of the internal jugular vein consist of three layers:

  • The tunica adventitia, or the outermost layer of the vein's wall, is the thickest of all layers. It is composed of loose connective tissue that connects to other tissues in the body
  • The tunica media, or middle layer, is made up of collagen, elastic fibers, and smooth muscle
  • The tunica intima, or innermost layer, is the thinnest layer of the vein’s wall, and is composed of an internal elastic membrane and connective tissue

The internal jugular vein has a dilated portion at its beginning, called the superior bulb, and another dilated portion at its end, called the inferior bulb, that connect with other veins.

The internal jugular vein also contains the internal jugular vein valve near its end to promote blood flow in one direction toward the heart and prevent backflow toward the brain.

Location

There is an internal jugular vein on both the right and left sides of the neck that originates from an opening on each side of the skull called the jugular foramen. The internal jugular vein dilates at its origin to form the superior bulb of the internal jugular vein, and is a direct continuation of the sigmoid sinus that drains blood from the brain.

The internal jugular vein runs vertically down each side of the neck behind the sternocleidomastoid muscle within the carotid sheath, a tube of connective tissue that runs from the base of the skull to the first rib. The carotid sheath surrounds the internal jugular vein, common carotid artery, and vagus nerve on each side of the neck. The left jugular vein is generally smaller than the right jugular vein.

The end of the internal jugular vein dilates to form the inferior bulb of the internal jugular vein, which contains the internal jugular vein valve. The internal jugular vein comes together with its smaller counterpart, the external jugular vein, and the subclavian vein to form the right and left brachiocephalic, or innominate, veins positioned behind the area where the clavicle meets the sternum

The brachiocephalic veins join together to form the superior vena cava, a large vein that directly drains all the deoxygenated blood from circulation of the head, neck, and arms into the right atrium of the heart to be pumped to the lungs to become oxygenated again.

Function

Blood Flow

The internal jugular vein is the largest vein in the neck and is the main source of venous drainage, or blood flow, down from the brain, returning deoxygenated blood back from the head and neck to the heart, where it will be pumped to the lungs to become oxygenated again.

The internal jugular vein also serves as the main channel to drain blood from the face and neck via the inferior petrosal sinus, facial vein, lingual vein, pharyngeal vein, and superior and middle thyroid veins that empty into it.

Central Venous Pressure

Evaluating the pulse via the internal jugular vein, called the jugular venous pulse, is a useful indicator for indirectly assessing central venous pressure, a measurement used to diagnose many heart conditions. Jugular venous pressure results from the expansion and contraction of the internal jugular vein that occurs with pressure changes in the right atrium of the heart.

Backflow of Blood

The internal jugular vein contains the internal jugular vein valve located near the vein’s end where it connects to the brachiocephalic vein. The internal jugular vein valve prevents backflow of blood from going back into circulation in the brain.

With a strong Valsalva maneuver (taking a large breath and holding it in), the internal jugular vein valves can malfunction due to the increased pressure. This can subsequently increase the blood pressure in the head as the blood backflows into the brain.

When there is a reduction in blood flow through the internal jugular veins, commonly observed in patients with head injury, cerebral hemorrhage, brain tumors, and hydrocephalus, blood can also backflow into the brain. This causes the cerebral blood volume of the brain to increase and results in increased intracranial pressure. If left untreated, increased intracranial pressure can cause serious brain damage.

Internal jugular vein blood flow can also be disrupted from compression caused by an enlarged thyroid gland, tumors, or abnormalities with the surrounding blood vessels and valves.

Clinical Significance

Conditions involving the internal jugular vein affect proper blood flow down from the head and neck, and can cause serious complications with backflow of blood and increased intracranial pressure in the brain.

Complications affecting the internal jugular vein include:

  • Stenosis, or narrowing, of the internal jugular vein can occur in patients with thoracic outlet syndrome, where nerves and blood vessels in the neck and/or shoulder become compressed from surrounding structures. Physical therapy or surgical measures can help decrease compression of the internal jugular vein
  • Aneurysm, or dilation of a blood vessel at least 1.5 times its normal diameter, occurs from weakening of the blood vessel walls. It occurs more commonly in arteries than in veins, but can occur in the internal jugular vein and increase the risk of vein rupture and hemorrhage. Surgery can be performed to treat an internal jugular vein aneurysm, where an excision venotomy is performed to cut through and repair part of the wall of the vein
  • Thrombosis, or blood clot, in the internal jugular vein can result in an enlarged neck mass on the side of the neck with swelling, redness, and pain. An internal jugular vein thrombosis is rare as the blood vessels in the head and neck are less susceptible to clotting because gravity aids in their blood flow down back to the heart. An internal jugular vein thrombosis is a potentially fatal condition that can result from cancer, infection, or central venous catheterization, although symptoms may be vague or absent altogether. Treatment includes oral blood thinner medication for several months to decrease the clotting
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