Anatomy

In order to begin to fully understand oropharyngeal cancer, it helps to understand the anatomy of the region. The oropharynx is part of the throat (along with the nasopharynx and hypopharynx) and is located in the very back of the mouth. The nasopharynx is located above the oropharynx, while the hypopharynx is located below. The oropharynx is made up of four different regions:

  • Tonsils
  • Base of tongue
  • Soft palate
  • Posterior pharyngeal wall

Tonsils

Tonsil - Palatine tonsil

The tonsils, also called the palatine tonsils, are the walnut-shaped structures located on either side of the back of the throat in the oropharynx. They are made up of lymphoid tissue, which contains infection-fighting immune cells, and they tend to swell up when someone is sick. The tonsils can cause problems such as recurrent infections (e.g. Strep throat), snoring, or a sleeping disorder known as obstructive sleep apnea, and often have to be removed.  One of the most common surgeries in the U.S. is the removal of enlarged tonsils in children. Interestingly, removing the tonsils does not hinder the body’s ability to fight infections, as the tonsils do not play a critical role in the body’s immune system. In general, each tonsil on either side of the throat should be about the same size (though some asymmetry can be normal).

In addition to palatine tonsils, there is a ring of tonsil-like tissue, called Waldeyer’s ring, located in the oropharynx. The bottom portion of the ring at the base of tongue is called the lingual tonsils (see below). As mentioned above, the  palatine tonsils make up the sides of the ring, and the pharyngeal tonsils, also known as the adenoids, form the top of the ring, located near the roof of the nasopharynx.

Some additional structures that are related to the tonsils include:

Tonsil - Soft palate
  • Anterior tonsil pillar
    This is the fold of tissue just in front of the tonsils. It is created by the palatoglossus muscle which extends from the soft palate down to the tongue.
  • Posterior tonsil pillar
    This is the fold of tissue just behind the tonsils. It is created by the palatopharyngeus muscle which extends from the soft palate to the lateral wall of the pharynx.
  • Glossotonsillar sulcus
    This is the bottom part of the tonsils where they blend into the lingual tonsil tissue on the back of the tongue. It is basically the area between the tonsils and the base of tongue.
  • Tonsillar fossa
    This is the “pocket” in which the tonsils sit. It is formed by the anterior and posterior tonsillar pillars.

Base of Tongue

Anatomy - Pharynx

The tongue is a thick, muscular organ that can be broken down into two main parts: the oral tongue and the base of tongue. These two parts are separated by a line of taste buds called the circumvallate papillae, with everything behind this line being part of the base of tongue and everything in front of it being part of the oral tongue.

The oral tongue is part of the oral cavity, and is visible when the mouth is open. It refers to the front two-thirds of the tongue. The oral tongue is capable of moving in multiple directions and also plays a critical role in articulation (or speech). It also helps to manipulate food during chewing and to prepare the food to be moved to the oropharynx.

The base of tongue is part of the oropharynx, and usually not visible when the mouth is open. The surface of this part of the tongue is lined with lymphoid tissue similar to the palatine tonsils, which are called the lingual tonsils. Underneath the tonsil tissue lies the muscle that is responsible for the movement of the tongue base. The base of tongue is very important for swallowing and protecting the airway by preventing aspiration.

Hyoid bone - Palate

Other anatomical structures related to the base of tongue include:

  • Vallecula
    This is the bottom end of the base of tongue, where it meets the epiglottis.
  • Lateral pharyngoepiglottic folds
    This is where the base of tongue transitions over to the side wall of the pharynx.

Soft Palate

The soft palate is the part of the roof of the mouth behind the hard palate . The uvula is a muscular appendage that hangs from the middle of the soft palate. The soft palate is made up of many muscles which move as someone breathes, eats, and speaks. The nasopharynx is above and behind the soft palate. When the soft palate moves up, or elevates, while eating or drinking, it closes the connection between the nasopharynx and the oropharynx, preventing food and liquids from going up into the nose. This action also prevents air from escaping into the nasal cavities during speech, causing hypernasal speech.

The lining of the soft palate is made up of a type of tissue called squamous epithelium, just like the rest of the throat and mouth. Under the squamous epithelium are minor salivary glands, nerves, blood vessels and lymphatics.

The deep portion of the soft palate is made up of five different muscles: 

  • Tensor veli palatini (TVP)
    This muscle is responsible for elevating the soft palate (in order to close off the connection between the nasopharynx and the oropharynx) and for opening up the Eustachian tube, which helps ventilate the middle ear space. It is controlled by a branch of the fifth cranial nerve (trigeminal nerve).
  • Levator veli palatini
  • Musculus uvulae
  • Palatoglossus (anterior tonsil pillar)
  • Palatopharyngeus (posterior tonsil pillar)

All of these muscles, except the TVP, are controlled by branches of the tenth cranial (vagus) nerve.

Posterior Pharyngeal Wall

Lingual tonsils - Tonsil

The posterior pharyngeal wall refers to the back wall of the oropharynx. It may be visible all the way at the back of the throat if a doctor asks a patient to stick out their tongue and say “ahhh.” The posterior pharyngeal wall is also lined with squamous epithelium similar to the soft palate. Just deep to the lining of the pharyngeal wall is a thin muscle known as the superior pharyngeal constrictor.  This muscle is controlled by branches of the tenth cranial nerve (vagus) and aids in swallowing. The upper part of the bony spine is located deep to the posterior pharyngeal wall musculature.

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