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Anatomy clinical correlates: Vessels, nerves and lymphatics of the neck

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Eyes, ears, nose and throat

Anatomy

Head
Neck
Cranial nerves
Transcript

The neck is a compact tube, containing many vital structures such as muscles, blood vessels, nerves, and lymphatics, as well as organs of the digestive and the respiratory tract. Now, the neck is like a sheath around these structures - however, it’s still an area prone to various injuries and conditions.

First of all, let’s discuss central venous access, which is when a catheter is placed in a large vein, usually the internal jugular or the subclavian vein. A central access is usually obtained when peripheral access isn’t available, like when an individual is severely hypovolemic, for example. If a patient will need intravenous access for a long period of time for medication delivery, such as chemotherapy, then central venous access is a great option to prevent repeated peripheral IV procedures or for those certain intravenous drugs that cause damage to peripheral veins. It can be used for fluid resuscitation, blood transfusions, central venous pressure monitoring, giving medications, hemodynamic monitoring or plasmapheresis. It can also be used when emergency dialysis is needed.

So first, let’s see how we go about accessing the internal jugular vein for central access. In order to better see the anatomy and maximize the internal jugular vein’s diameter, the individual should be in Trendelenburg position, which means that their head is down at about 15 degrees compared to the rest of the body. If the catheter is placed in the right internal jugular, then the head must be turned towards the left and vice-versa. Usually, for a catheter, the right internal jugular vein is preferred, because it has a more direct path towards the superior vena cava.

Now there are some important landmarks that we can use to help us identify the internal jugular vein. First, there’s the anterior cervical triangle, which is bordered inferiorly by the clavicle, medially by the sternal head of the sternocleidomastoid muscle and laterally by the clavicular head of the sternocleidomastoid muscle. So far, so good! Now, near the lateral side of the sternal head, you can palpate the carotid artery; with the internal jugular vein lying superficial and lateral to the carotid artery. Then the introducer needle is inserted at a 40 degree angle to the skin at the apex of the anterior cervical triangle, aiming towards the ipsilateral nipple.

Now let’s switch gears and look at how you can access the subclavian vein for central access. You guessed it - it’s landmark time! So, overlying the first rib, from anterior to posterior, there’s the clavicle, the subclavian vein, the anterior scalene muscle and then the subclavian artery. Medial to the junction of the medial and middle thirds of the clavicle is where you’ll find good exposure of the subclavian vein, where it is usually targeted for catheterization using an infraclavicular approach.

There are two insertion sites: either 1 to 2 centimeters inferior to the clavicle at the junction of the medial and middle thirds or just inferior to the clavicle at its midpoint. The needle is advanced beneath the clavicle toward the sternal notch. Bear in mind that central venous access does come with associated risks, such as pneumothorax, hematomas, damage to the veins, infection, or thrombosis.

In the same vein (pun intended!), let’s see how the jugular venous pressure and its flow dynamics can help us in clinical practice. Generally, the pulsations of the internal jugular vein can provide information about heart activity, specifically, the right atrium. The vein’s pulsations can be seen on the surface of the skin as it arises from beneath the sternocleidomastoid muscle superior to the medial end of the clavicle. There are no valves in the brachiocephalic vein or the superior vena cava, so when the right atrium contracts, there is blood flow that directly passes up these vessels to the inferior bulb of the internal jugular vein.

These pulsations can be better visualized when the individual is in Trendelenburg position and we usually observe the right internal jugular vein, because it has a more direct course to the right atrium and is therefore a better reflection of its pressure and activity. With very low jugular venous pressure, the patient will need to be near supine to appreciate it, while for an individual with very high jugular venous pressure we might actually see the pulsations going up to the earlobe even when the patient is upright!

After you’ve determined the location of pulsation of the internal jugular vein, the individual can lie flat on the bed and you can measure the jugular venous pressure which can then give us an estimation of pressure in the right atrium. You’ll need two rulers. Extend the first one horizontally from the highest pulsation point of the jugular vein and cross it perpendicularly with the other ruler that you’ll place vertically at the point of the sternal angle...just for example, let’s say we obtain 9 centimeters.

To use this measurement to estimate right atrial pressure, we add 5 centimeters, which is the distance in order to get to the center of the atrium from the sternal angle. So, in this case, our estimated right atrial pressure is 14 centimeters. The internal jugular pressure increases in conditions such as mitral valve disease, which increases pressure in the pulmonary circulation and the right side of the heart.

Okay, time for our first quiz. What are the anatomical landmarks used to identify the internal right jugular vein?

Great, let’s switch gears and talk about the thyroid ima artery. Approximately 10% of people have a small, unpaired thyroid ima artery which originates from the brachiocephalic trunk. It can also arise from the aorta, the right common carotid, the subclavian artery or from the internal thoracic arteries. It then ascends on the anterior surface of the trachea to the isthmus of the thyroid gland, where it supplies branches to both of these structures.

The location of this artery is important when performing a tracheostomy. That’s when a transverse incision through the skin of the neck and anterior wall of the trachea is made, in order to establish a patent airway in individuals with upper airway obstruction. Usually the opening is made in the trachea just between the first and second tracheal rings, the second and third, or third and fourth rings. Care must be taken in these procedures to avoid damaging the thyroid ima artery if it’s present as significant bleeding can result.

A similar sounding, but vastly different procedure, is a thyroidectomy, which refers to the surgical removal of the thyroid gland. A hemithyroidectomy, on the other hand, is the removal of only one half, or lobe, of the thyroid gland. During a thyroidectomy or a hemithyroidectomy, the inferior laryngeal nerve, which is the continuation of the recurrent laryngeal nerve, can be damaged, which damages the muscles that move the vocal fold.

This leads to paralysis or weakness of the one or both of the vocal folds. With unilateral paralysis, the voice is poor because the paralyzed vocal fold can’t adduct to meet the normal vocal fold. Within weeks, the other vocal fold will adduct across the midline to compensate. However, with bilateral vocal cord paralysis, the voice is almost absent. This also results in high pitched, noisy respiration known as stridor as the laryngeal inlet is narrowed and cannot move to widen itself.

Ok! Now, to switch things up a little bit, remember that the neck is divided into an anterior and a posterior triangle, mainly based on the borders of the sternocleidomastoid and trapezius muscles, as well as other muscular and bony structures found in the neck. These regions provide a clear anatomic map for localizing the structures, injuries or pathologies involving the neck.

The posterior triangle contains the spinal accessory nerve, or cranial nerve XI, which contributes to the innervation of the sternocleidomastoid and the trapezius muscles, so nerve injury results in diminished or absent function of these muscles. This can present as an asymmetric neckline, drooping shoulder, laterally displaced scapula, and weakness with overhead abduction of the shoulder.

Now, the spinal accessory nerve is very long and has a superficial course, which makes it particularly susceptible to injury. The most common cause of spinal accessory nerve injury is iatrogenic, meaning due to medical procedures, in particular radical neck dissections and cervical lymph node biopsies. Other less common causes include blunt or penetrating trauma to the region, and in some causes, spinal accessory nerve injury may happen spontaneously.

The posterior triangle also contains the brachial plexus, and serves as an access point for this set of nerves which can really come in handy. One very important technique is the interscalene nerve block, which refers to the placement of local anesthetic around the roots or trunks of the brachial plexus at the level of the C6 vertebral body, between the anterior and middle scalene muscles.