Triangles of Neck

by Stuart Enoch, PhD

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    00:01 Okay, so that’s your midline. That brings you the triangle of the neck. I’m sure you will know the basic thing.

    00:13 That's your sternocleidomastoid, trapezius, midline, here, and that's your angle of mandible.

    00:19 Okay, so these are your two big triangles. What are the subtriangles in the neck? So, what are the subtriangles here? Submandibular? Submandibular. What are the boundaries? You're right, submandibular.

    00:38 Angle of the mandible. Angle of the mandible.

    00:41 Anterior border of the sternocleidomastoid. Eh… no.

    00:48 I forgot this. Okay, someone else? What are the triangles? Just name the triangles in the neck? Carotid.

    00:55 Carotid, yup. Digastric.

    01:01 Digastric, okay. Submental.

    01:05 Submental. A lot of names coming out. Fine. The easiest way -- The easiest way is to identify the hyoid bone okay? You have the posterior belly of the digastric coming from here, swings around the hyoid and then you have the anterior belly of the digastric. So if you take it from both sides, that forms your submental triangle. Okay? What are the important structures in the submental triangle here? Pretty much nothing really. You just have some lymph nodes, some fat, you can probably feel the facial artery at the edge of the triangle, but apart from that nothing significant.

    01:54 The next triangle you see here is the submandibular triangle, which is formed by the anterior belly of the digastric, posterior belly of the digastric and the ramus of the mandible. That's one important triangle because you have the submandibular glands, submandibular lymph nodes, what else? If you are asked to do a lymph node biopsy from that area, or you do excision of a lipoma, what are the things you're worried about? What are the structures that can be affected? In the submandibular? Yeah here. We're here.

    02:35 Submandibular? Is it retromandibular vein? Retromandibular vein is quite posterior.

    02:40 Lingual nerve? Lingual nerve, one. What else? You’re right, what else can you think of? Hypoglossal nerve and nerve to mylohyoid. So lingual nerve, nerve to mylohyoid, hypoglossal, submandibular gland and submandibular lymph nodes. They are all in the submandibular triangle. That’s quite important. Okay, you mentioned the lingual nerve? Where does the lingual nerve come from? From the facial nerve? Not from the facial. Mandibular? No. Hypoglossal? No. I think I’ll just stop there. I made it confused with all these answers.

    03:34 I’ll probably come back to lingual nerve when we discuss a bit more. Fine, we’ll just remember the lingual nerve for now. What does the lingual nerve supply? What does it do? Tongue. Yeah, what in the tongue? Sensory, motor or taste? Sensory? Sensory? Sensory to what? 2/3rd.

    03:55 Anterior 2/3rd of the tongue. Okay, so because we’re already there, we’ll just cover the tongue as well. Okay, so tongue, what you need to know for the exam is the motor supply, sensory supply and taste. The whole of the tongue is by hypoglossal nerve. Motor.

    04:14 So the protrusion of the tongue, movement of the tongue, etc. is by the hypoglossal nerve. It is divided into posterior 1/3rd, anterior 2/3rd. The posterior 1/3rd, both taste and sensation is by glossopharyngeal. In the anterior 2/3rd, taste is by chorda tympani and sensory is by lingual. Where does the chorda tympani nerve come from? Facial. Facial. Okay. So these are things you need to remember in your submandibular gland. Then you mentioned about the carotid triangle, which is right. The carotid triangle. This is your carotid triangle. Okay? What are boundaries of the carotid triangle? Of the? Sternocleidomastoid. Sternocleidomastoid, um, I can’t remember.

    05:21 Posterior belly of digastric. And, is it on the midline? It’s not on the midline, because you have a muscular triangle as well.

    05:31 Omohyoid? Which one? The anterior? Superior belly. Superior belly of the omohyoid.

    05:37 That’s the superior belly of the omohyoid and this the inferior belly of the omohyoid, going into scapula. So this is the carotid triangle and this one is the called your muscular triangle. That’s where the strap muscles are. Okay, that’s your muscular triangle where the strap muscles are. Okay so this your carotid triangle. Clearly you have the carotid artery, internal jugular vein, vagus. Three mega structures, they are all in the carotid sheath. Anything else you can think of? You have the ansa cervicalis. The ansa cervicalis, what we discussed, that is embedded on the carotid sheath, mainly the superior part of the ansa cervicalis going to the strap muscles. Okay? They are all in the carotid triangle. In the muscular triangle, we discussed, there are the strap muscles. Posterior triangle, if you understand trapezius, sternocleidomastoid, then your inferior belly of the omohyoid divides into an occipital triangle which is here and a supraclavicular triangle. What are the structures here? Important structures in the occipital triangle? Lymph nodes? What else? Accessory nerve? Very good. Spinal accessory nerve. Is it superficial or deep? Deep? No, spinal accessory nerve is very superficial. I can’t see in his neck but in some people you would be able to see the external jugular vein, particularly in children when they cry, you can see the external jugular vein, that you can use for cannulation as well. So the external jugular vein lies here and the spinal accessory nerve runs along with the external jugular vein and it’s a very superficial structure.

    07:28 In this part of the neck, when we’re looking here, you don’t have any important structure at this point. Spinal accessory nerve. As you come down, as you can see here you have the triangle of the brachial plexus. Okay? What about the supraclavicular fossa, or the supraclavicular triangle? What are the important structures here? You imagine if somebody is stabbed or got an injury at this point? What are the things will injure? Subclavian artery. Which one? Subclavian artery? What did you say about the pleura? The cupola.

    08:04 The cupolar or the apex of the lung. Is the apex of the lung here or not? It’s on the medial side. The apex of the lung is the medial 2.5 cm of the clavicles. So the apex of the lung is here. If somebody is stabbed there, then you have a pneumothorax, but if you’re coming more laterally you have the brachial plexus, subclavian artery, subclavian vein.

    08:31 These are the important structures. This is what will be asked in your exam at this point.

    08:36 If the same injury happens on the left side, there’s an additional structure.

    08:41 Thoracic duct? Thoracic duct, okay very good. Tell me about thoracic duct. You’re right. Tell me a little bit more about thoracic duct, what does it do? Where does it drain? It starts from the right hand side and then crosses over to the left. What does it drain? Below the diaphragm? From where? Below the diaphragm. Very good.

    09:00 So all the lymphatic drainage from the lower limb and the abdomen is collected into the sac called cisterna chyli, cisterna chyli, which is located in front of the L2 vertebra from which you have the thoracic duct. So thoracic duct is quite lower down, then it pierces the diaphragm at what vertebral level? T12? T12. Along with the abdominal aorta, ascends up the mediastinum, comes up all the way to the angle of Louis which is lower border of the T4 vertebra or the second intercostal space, then crosses over from the right to the left and empties into the junction of the subclavian vein versus the internal jugular vein. That’s where the thoracic duct drains.

    09:55 So, if somebody sustains a stab wound to this part here, you have the thoracic duct. Okay? As well as apex of the lung. It’s very specific on the left side.

    10:13 Okay. Now we’ll just move up a little bit from the neck, to the lymph nodes back to submental area.

    About the Lecture

    The lecture Triangles of Neck by Stuart Enoch, PhD is from the course Head and Neck Anatomy—MRCS.

    Author of lecture Triangles of Neck

     Stuart Enoch, PhD

    Stuart Enoch, PhD

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