Anatomy clinical correlates: Viscera of the neck

The neck houses a number of important anatomical structures and serves as the gateway between our head and body. These structures include major blood vessels and nerves, parts of the respiratory and digestive tract, as well as important endocrine glands such as the thyroid and parathyroid glands. However, the neck is very exposed and vulnerable to injury, and all of these important structures in the neck are susceptible to a variety of clinical conditions. So take a quick moment, stretch out your neck, and let's get started!

Let's begin with the thyroid gland. When there is abnormal growth of the thyroid gland, it is called a goiter. When the gland gets big enough, it can be seen as a bulge in the lower part of the neck, and may even extend deep to the sternum. Causes of a goiter include iodine deficiency, autoimmune disorders such as Hashimoto’s thyroiditis and Graves disease, thyroid cancer, or a thyroid cyst. 

The thyroid gland can enlarge anteriorly, posteriorly, inferiorly, laterally, or even substernally, but it won't enlarge superiorly because of the superior attachments of the overlying sternothyroid and sternohyoid muscles. 

If it enlarges, it has the potential to compress nearby structures such as the trachea, causing difficulty breathing; the esophagus, leading to difficulty swallowing; the recurrent laryngeal nerves, leading to hoarseness; as well as the jugular veins, leading to thrombosis and superior vena cava syndrome in rare cases. 

Another condition that causes swelling of the neck is a thyroglossal duct cyst, which is the most common congenital cyst in the neck. This condition occurs because during development, the thyroid gland actually develops in the floor of the embryonic pharynx in a small area identified as the foramen cecum which is found on the dorsum of the tongue. During development, the thyroid gland migrates from the tongue into the neck passing anterior to the hyoid bone through the thyroglossal duct. This duct attaches the developing thyroid gland to the foramen cecum and normally disappears after birth, however, sometimes parts of this duct remain, and a thyroglossal duct cyst can form along any part of it.

This cyst is usually located along the midline of the anterior neck, close or just inferior to the hyoid bone, and can form a visual and palpable mass. Most cysts are asymptomatic, but sometimes they can cause neck pain and dysphagia. Other complications include infections or rupture, where rupture can lead to a thyroglossal fistula. In rare cases, a thyroglossal duct cyst carcinoma can develop from the ectopic thyroid tissue within the cyst. Clinically, the neck mass will move with swallowing or tongue protrusion as the duct is tethered to the tongue, which is the way to distinguish it from other neck swellings. 

Now, when a tumor of the thyroid is diagnosed, partial surgical removal of the gland called a partial thyroidectomy, or complete removal called a thyroidectomy, is required. However during a thyroidectomy, caution is needed in order to prevent damage to other important surrounding structures. 

For example, sometimes the parathyroid glands can also be removed during a thyroidectomy due to their small size and variable location within the thyroid gland, particularly the inferior parathyroid glands. Removal of the parathyroid glands will lead to hypoparathyroidism and can result in tetany, which is a severe neurologic syndrome caused by low calcium levels in the blood due to the decrease in parathyroid hormone. This manifests as muscle twitches, cramps, and contractions, and sometimes can even progress to death if the laryngeal and respiratory muscles are involved. 

To prevent removal of the parathyroid glands during a thyroidectomy, surgeons usually preserve the posterior part of the lobes of the thyroid gland. If that’s not possible, the parathyroid glands are carefully isolated with their blood vessels intact, and can be transplanted back into the body, for example into the arm so they won’t be damaged by subsequent thyroid surgery or radiation therapy. 

Also remember, during a thyroidectomy a few other structures can be damaged as well. The recurrent laryngeal nerves run near the inferior pole of the thyroid gland and pass near the inferior thyroid artery, which needs to be ligated and cut, as well as the the external branch of the superior laryngeal nerve, which may be damaged, during removal of the superior portions of the thyroid gland. 

Ok then! Now let’s switch gears and look at the larynx, which is responsible for voice production and maintaining a patent airway. The larynx contains the vocal cords and the rima glottidis which are responsible for voice production. In fact, the pitch of the voice is changed by variations in the tension and length of the vocal folds, the width of the rima glottidis, and the intensity of the expiratory effort. However one of the greatest changes to the larynx occurs during puberty. 

During puberty in biological males, the increased production of testosterone strengthens the walls of the larynx and enlarges the laryngeal cavity, where in biological females the size of the larynx only slightly increases. Furthermore in biological males, the laryngeal cartilages enlarge and the laryngeal prominence becomes more apparent. The anteroposterior diameter of the rima glottidis almost doubles its size and the vocal folds become longer and thicker. This is the reason why the voice in biological males typically becomes lower pitch after puberty - and why there’s that awkward transition stage while the anatomy of the larynx matures during puberty!

So can you recall a few causes of a neck mass? How about the structures damaged during a thyroidectomy? 

Let's talk a bit more about the larynx. Now, everyone loves to hear someone who is good at singing, but have you ever wanted to take a look at their vocal cords to see what makes them an amazing singer? Or maybe take a look at what makes your friend who never stops singing a bad singer? Ok, looking at the vocal cords might not tell us what makes a good singer, but visualizing the larynx can help us identify a variety of clinical conditions. 

To look at the larynx a laryngoscopy can be performed, which is a procedure that helps visualize the interior of the larynx. This can be done under direct laryngoscopy, when the larynx is examined with a tubular endoscopic instrument, called a laryngoscope. Laryngoscopy is indicated in many clinical scenarios. It may be needed in acute scenarios during respiratory compromise in order to facilitate tracheal intubation, or intubation during general anesthesia. It can also be used to visualize the larynx if cancer is suspected, or visualize the vocal cords to investigate vocal cord pathology such as polyps or paralysis.