Video: Triangles of the neck

The neck, or the cervical region, is perhaps one of the most anatomically complex regions of the body. Despite being a relatively small region, the neck certainly packs in a large amount of structures such as muscles, blood vessels, and nerves. But is there a way to organize and remember all these structures? Well, fortunately, there is, and today, we’re going to be exploring just that as we learn about the triangles of the neck.

The triangles of the neck are simply an organization method that parcels or compartmentalizes the vast amount of anatomic detail that is found in the anterior and lateral aspects of the neck into manageable and easy to remember study units – a trail map to the neck if you like. So, in this tutorial, we’re going to be examining each of the triangles of the neck and we’re going to learn about the anatomical landmarks and structures that we can see in and around these triangles.

When we’re looking at the anatomy of the neck, we must remember that the neck can be divided into two symmetrical halves by the median line of the neck which runs from the mandibular symphysis down to the manubrium of the sternum. So when we’re looking at the triangles of the neck, don’t forget in most cases, there will be two of the same triangles – a left one and a right one.

If we change to a lateral view of the neck and remove the skin, the platysma, and the superficial layer of deep cervical fascia, we can now get a better appreciation for the structures that bound and course within these triangles. The triangles of the neck can be divided into two main groups – the anterior triangle and the posterior triangle – where the point of division is at the sternocleidomastoid muscle, which is the big muscle that bulges out when you turn your head from side to side. We’ll first discuss the anterior triangle of the neck which encompasses the area of the neck as seen here highlighted in green.

The anterior triangle is bordered laterally by the sternocleidomastoid muscle whose muscle belly can be seen just here, and it’s bordered medially by the median line of the neck which we saw earlier and superiorly by the body of the mandible which makes up the lower jaw. And you can imagine that the apex of the anterior triangle is pointing towards the manubrium of the sternum.

The anterior triangle of the neck is further divided into smaller triangles – the submandibular triangle, the submental triangle, the carotid triangle, and the muscular triangle – which will be discussed shortly.

Let’s now have a look at the submandibular triangle, which is situated inferior to the mandible where the submandibular glands are located just as the name suggests. The triangle is bordered superiorly by the mandible and the anterior and posterior bellies of the digastric muscle. The floor of the submandibular triangle is made by the mylohyoid muscle as well as the hyoglossus muscle which also forms the floor of the oral cavity. The triangle is also covered by the skin, fascia, and the platysma, which is the thin superficial muscle of the neck and the covering or the roof of all the triangles will be the same.

The submandibular triangle contains many structures, therefore, making it an important anatomical location. The mylohyoid muscle divides the submandibular triangle into a superficial and deep compartment, and in the superficial layer of the triangle, you’ll find the submandibular gland and its lymph nodes. The facial artery with its corresponding vein runs through the gland and gives off a branch called the submental artery, which will supply the chin area together with the submental vein. The mylohyoid nerve, which arises from the mandibular branch of the trigeminal nerve innervates the mylohyoid muscle and the anterior belly of the digastric muscle and can also be found in the submandibular triangle.

In the deep layer of the submandibular triangle, the geniohyoid muscle that is seen in the midline of the floor of the oral cavity, and the hyoglossus muscle, which is one of the tongue muscles, are seen. And this small highlighted lingual artery and vein can also be found in the deep layer of the submandibular triangle.

We’re going to change to an anterior view of the neck again for a moment to view the second anterior triangle which is the submental triangle, seen here medial to the submandibular triangles. And this triangle is a median triangle, meaning that it is located on the midline of the neck, and occupies both the superior portions of the right and left anterior triangles. And this submental triangle is bordered laterally by the two anterior bellies of the digastric muscles and inferiorly by the hyoid bone. And the body of the hyoid bone forms the triangle’s base and the apex of the triangle points towards the mandibular symphysis. And the floor is formed by the mylohyoid muscle and is covered by the platysma, fascia, and the skin just like the submandibular triangle.

The submental triangle is very small and contains small veins such as the submental veins that drain to the anterior jugular vein. And these structures that are found in the triangle include the submental lymph nodes seen here highlighted in this picture looking up towards the chin on top of the mylohyoid muscles.

The next triangle is different from the other two triangles that we’ve discussed as the two muscular triangles share a border at the median line of the neck. The muscular triangle which is also known as the omotracheal triangle is bordered superiorly by the hyoid bone, superolaterally by the superior belly of the omohyoid muscle, and inferolaterally by the sternocleidomastoid muscle, and the base of the triangle will be the shared median line of the neck as we have discussed earlier. The apex of the triangle will be at the point where the sternocleidomastoid and the superior belly of the omohyoid muscles intersect.

In this triangle, we’ll find a number of structures including the infrahyoid muscles and these include the thyrohyoid, the sternothyroid, and the sternohyoid muscles and also in this area, you’ll be able to find some important organs and these include the thyroid gland and the parathyroid gland, which makes important hormones for the proper functioning of the body.

The vessels supplying the organs will also be found in this area such as the superior thyroid artery and vein, the inferior thyroid artery and vein, and the anterior jugular vein.

The last triangle of the subdivisions of the anterior triangle is the carotid triangle which is an important anatomical landmark as it contains some important vessels and nerves. It is bordered anteriorly by the superior belly of the omohyoid muscle, superiorly by the posterior belly of the digastric muscle, and posteriorly by the anterior border of the sternocleidomastoid muscle. The floor is made by part of the thyrohyoid muscle which is this short muscle below the hyoid bone, the hyoglossus muscle which is the muscle above the hyoid bone, and by the middle and inferior constrictors of the pharynx.

The carotid triangle is also covered by the deep and superficial fascia, platysma, and the skin as with all the other triangles.

So in the carotid triangle, there’s an important structure called the carotid sheath, which is a fibrous connective tissue sheath that is part of the deep cervical fascia of the neck surrounding the vessels and the nerves that we’re now going to discuss. And this sheath contains the common carotid artery which is located medially in the sheath, the internal jugular vein which is located laterally, and the vagus nerve which is found posteriorly between the vessels. Now, the carotid sheath may also contain deep cervical lymph nodes and this is also an important place to note as it’s the place where the common carotid artery bifurcates into the external and internal carotid arteries.

So, there’s a few other structures that are found in the carotid triangle, and I want to talk about these in the next few minutes. So, several branches of the external carotid artery are found within this triangle such as the superior thyroid artery, the lingual artery, the facial artery, the ascending pharyngeal artery, and the occipital artery. The veins that drain into the internal jugular veins are also found in the carotid triangle, and they mostly correspond to the arteries that we mentioned previously.

The nerves found in this triangle are the hypoglossal nerve which is located superficial to the carotid sheath which is a small portion of the accessory nerve, and the ansa cervicalis which is a looped nerve superficial to the internal jugular vein and the common carotid artery.

We’ll now have a look at the posterior triangle and it’s located in the lateral part of the neck as you can see in this picture.

The posterior triangle is bordered anteriorly by the posterior border of the sternocleidomastoid muscle, posteriorly by the anterior border of the trapezius muscle which is part of the back muscles, and inferiorly by the clavicle. The floor of the triangle is formed by the prevertebral fascia which covers some muscles that also make the floor of the posterior triangle such as the splenius capitis, the levator scapulae, and the anterior, middle and posterior scalene muscles.

The triangle is covered by the investing layer of the deep cervical fascia and the inferior belly of the omohyoid crosses the posterior triangle dividing it into a small supraclavicular triangle and a large occipital triangle.

Let’s talk now about the supraclavicular triangle, which is also known as the omoclavicular triangle or the subclavian triangle. And this triangle is bordered superiorly by the inferior belly of the omohyoid muscle, anteriorly by the sternocleidomastoid muscle, and inferiorly by the clavicle. And the floor of this triangle is largely formed by the anterior and middle scalene muscles while it is covered the same as all the other triangles as we have discussed earlier in the video.

In this space, you can find the distal part of the subclavian artery located between the anterior and the middle scalene muscles which is this long muscle that you can see on the lateral side of the neck, and if you can, think of the scalene muscles looking like a tent over the artery. The transverse cervical artery running superficially along the two scalene muscles and the dorsal scapular artery with their veins can also be found in this supraclavicular triangle and the external jugular vein into which the retromandibular and posterior auricular veins drain is located superficially behind the sternocleidomastoid muscle and finally drains into the subclavian vein.

This triangle also contains a portion of the brachial plexus and its branches and the cervical plexus and its branches such as the phrenic nerve which innervates the diaphragm. The supraclavicular lymph nodes can also be found in this space which is an important clinical marker that will be discussed at the end of the video.

Above the supraclavicular triangle is the larger occipital triangle, also known as the omo-trapezius triangle, and this is the second part of the posterior triangle of the neck. It’s bordered anteriorly by the posterior border of the sternocleidomastoid muscle, posteriorly by the trapezius muscle, and inferiorly by the inferior belly of the omohyoid muscle. And the floor is made by the splenius capitis, the levator scapulae, and the middle scalene muscle.

In this triangle, vessels such as the occipital artery and the transverse cervical artery with its veins can be seen, and there are many nerves that can be found in the occipital triangle like the accessory nerve which runs in front of the sternocleidomastoid muscle and pierces it, and the upper part of the brachial plexus and the cutaneous branches of the cervical plexus and the phrenic nerve running down the anterior scalene muscle innervating the diaphragm are also found in this space.

So, we’ve now gone through the most important triangles of the neck, and for our clinical note today, we’re returning to the supraclavicular triangle of the posterior triangle of the neck, specifically that found on the left side. So, this triangle is clinically relevant as it’s, for example, a common site for the palpation of pathologically enlarged lymph nodes.

So as we mentioned earlier, the left supraclavicular lymph node which is found posterior to the clavicular head of the sternocleidomastoid muscle which I’ve just removed, has a significant clinical importance. So, this node which is also sometimes known as Virchow’s node, the left supraclavicular node drains lymph much of the body in particular the abdominal cavity. And if this lymph node becomes enlarged and hard, it’s known as the Troisier’s sign, which is often an indication of presence of advanced abdominal cancer, commonly gastric or pancreatic cancer, which has metastasized along the lymph vessels.

Knowledge of triangles of the neck is also of great importance for the evaluation of pulses in the cardiovascular examination. Within the carotid triangle, the carotid artery pulse can be measured to determine the central pulse, which can also be compared to the radial artery pulsation measuring the peripheral pulse. The carotid triangle also contains the carotid sinus which has sensory cells called baroreceptors that sends stretch of the artery and by feedback mechanism regulates the blood pressure.

External massage called the carotid sinus massage can also be used to slow the heart rate and decrease the blood pressure for diagnostic purposes and in emergency cases of supraventricular tachycardia.

So thanks for sticking with me throughout this tutorial. We’ve now reached the end. Let’s go over some key points that you should know.

So we’ve gone through the borders and the contents of the triangles of the neck which is very important to know as they can be good anatomical landmarks during clinical practices. And I’m just going briefly mention the main triangles and their subdivisions that have been mentioned in this tutorial.

So the triangles of the neck can be divided majorly into the anterior and the posterior triangles of the neck and firstly, the anterior triangle can be further divided into the submandibular, the submental, the muscular, and carotid triangle, while the posterior triangle can also be divided into the smaller supraclavicular and the larger occipital triangle.

So now we’ve reached the end of the tutorial. Thanks for sticking with me and happy studying!