Pharynx Anatomy

Updated: Nov 18, 2013
  • Author: Arjun S Joshi, MD; Chief Editor: Thomas R Gest, PhD  more...
  • Print
Overview

Overview

The pharynx is a fibromuscular tube that is semicircular in cross section and is situated directly anterior to the vertebral column. It extends from the skull base to the lower border of the cricoid cartilage. Six muscles are predominantly responsible for the voluntary actions of the pharynx: three pharyngeal constrictor muscles that are roughly circularly layered on top of one another and three vertically oriented muscles (stylopharyngeus, salpingopharyngeus, and palatopharyngeus). These muscles aid in the act of swallowing. [1]

The pharynx serves as a continuation of the digestive cavity, providing a route from the oral cavity proper to the esophagus. In addition, the pharynx communicates with the nasal cavity, the middle ear cavity, and the larynx. The pharynx is often described from an exterior view and an interior perspective. Based on the location, the interior of the pharynx is often separated into three sections—the nasopharynx, oropharynx, and laryngopharynx. [2]

The video below shows a view of the pharynx through the mouth.

A view of the pharynx through the mouth. The patient is supine on the operating room table. A Crowe-Davis mouth gag has been placed in the patient's mouth to open and expose the oropharynx. At the superior aspect of the pharynx (bottom of the screen) is the inferior aspect of the soft palate with the dangling uvula. The large structures on the lateral aspect of the pharynx are the tonsils. The posterior aspect of the pharynx is lined by the posterior pharyngeal wall and soft tissue that covers the cervical spine. The tongue is retracted by the mouth gag and is visible in the top of the picture. The base of tongue forms the base of the pharynx. The base of tongue contains the lingual tonsils. Video courtesy of Ravindhra G. Elluru, MD, PhD.
Next:

Gross Anatomy

To best interpret the anatomy of the pharynx, the pharynx is often divided into exterior and interior sections. The external surface is typically described from posterior and lateral views and includes external surface muscles that compose the wall of the pharynx, associated nerves, and blood supply. However, the interior of the pharynx is typically described from either a sagittal cross-section or a posterior view as a dissection in which the external wall of the pharynx is split midline. The remaining halves are retracted laterally to reveal the internal anatomical landmarks and muscles of nasopharynx, oropharynx, and laryngopharynx. [3] The following sections describe the exterior and interior pharynx in detail.

Exterior of the Pharynx

From the posterior view, the exterior surface of the pharynx lies anterior to the cervical vertebrae. It connects to the occipital bone anterior to the foramen magnum. The exterior surface of the pharynx consists of voluntary muscle covered externally by a fine buccopharyngeal fascia, which is continuous with the external surface of the buccinator muscle.

Found directly on top of the buccopharyngeal fascia are the pharyngeal venous plexus and the pharyngeal nerve plexus. Posterior to the buccopharyngeal fascia but anterior to the alar fascia (prevertebral fascia), a loose connective tissue-occupying space exists, known as the retropharyngeal space. Specifically, the retropharyngeal space extends superiorly to the skull base and inferiorly to the infrahyoid region of the neck.

Within the retropharyngeal space slightly superior to the bifurcation of the carotid artery is a large retropharyngeal lymph node along with minor lymph nodes that drain most of the pharynx’s lymphatics. Continuous with the retropharyngeal space but extending laterally around the pharynx exist the left and right parapharyngeal spaces. The parapharyngeal spaces are bound superiorly by the skull base, but unlike the retropharyngeal space extend inferiorly only to the sheath of the submandibular gland in the suprahyoid region. These spaces are bound medially by the pharynx and laterally by pterygoid muscles of the infratemporal fossa and the parotid fascia.

The exterior wall of the pharynx consists primarily of four muscles: superior pharyngeal constrictor, middle pharyngeal constrictor, inferior pharyngeal constrictor, and stylopharyngeus. The three pharyngeal constrictors muscles are quite simply arranged as they overlap each other in a vertical arrangement. Although the three pharyngeal constrictor muscles have different origins anteriorly, their fibers all insert in the midline posteriorly to form the pharyngeal raphe.

The superior pharyngeal constrictor muscle originates from multiple anatomical sites on the lateral aspect of the face prior to forming the posterior wall of the pharynx. Specifically, it originates from the posterior border of the pterygomandibular raphe, pterygoid hamulus of the sphenoid bone, posterior end of the mylohyoid line of the mandible, and lateral aspect of the tongue. Once the fibers reach the posterior aspect of the pharynx, they attach to the pharyngeal raphe, which attaches to the pharyngeal tubercle on the occipital bone.

Above the superior constrictor muscle exists the pharyngobasilar fascia, serving as an attachment for the pharynx to the skull base. The pharyngobasilar fascia is defined as a distinct submucosal membranous fascia that lies between the muscle and mucosal layers of the pharynx wall. It has attachments to the basilar part of the occipital bone, the petrous part of the temporal bone anterior to the carotid canal, the border of the medial pterygoid plate, and lastly to the pterygomandibular raphe. The levator veli palatini muscle, the cartilaginous end of the auditory (Eustachian) tube, and the ascending palatine artery pierce the pharyngobasilar fascia above the upper border of the superior pharyngeal constrictor muscle.

The middle pharyngeal constrictor muscle lies directly below the superior pharyngeal constrictor. Specifically, it originates from the stylohyoid ligament as well as from the greater and lesser horns of the hyoid bones. As the fibers of the middle pharyngeal constrictor muscle spread posteriorly, a portion of the fibers overlap the superior constrictor muscle and the remaining fibers are overlapped by the inferior pharyngeal constrictor muscle.

The inferior pharyngeal constrictor muscle is separated into two separate muscles, the thyropharyngeus and cricopharyngeus, because they have different origins, insertions, and functions. As the name implies, the thyropharyngeus originates from the thyroid cartilage and inserts into the pharyngeal raphe. However, the cricopharyngeus originates from the lateral surface of the cricoid cartilage. Unlike the other pharyngeal constrictors, the lower fiber of the cricopharyngeus bypasses the pharyngeal raphe and inserts itself into the circular fibers of the esophagus. Due to its insertion point, the cricopharyngeus muscle serves as a superior esophageal sphincter. It is in a state of tonic contraction until swallowing is initiated to prevent regurgitation of gastric and esophageal contents into the pharynx.

Increased tone of the cricopharyngeus has a role in the development of Zenker false diverticulum, where increased pressure causes extravasation of a mucosal pouch in a weak area of pharyngeal wall. Most of the time, this occurs at the Killian triangle, which is a small area between the thyropharyngeus and cricopharyngeus without musculature.

The stylopharyngeus muscle is the fourth exterior pharyngeal muscle. As the name implies, the muscle originates from the medial surface at the base of the styloid process of the temporal bone. Portions of the fibers merge between the superior and middle pharyngeal constrictors muscles and the rest insert on the posterior border of the thyroid cartilage.

With an understanding of the major muscles of the exterior pharynx, it is easier to delve into some detail about important associated structures, including nerves and vasculature. Superiorly and posterolaterally from the pharyngobasilar fascia, the jugular foramen serves as an exit site for cranial nerves IX, X, and XI. In relation to each other, cranial nerve IX exits the jugular foramen anterior to both cranial nerve X and cranial nerve XI. Cranial nerve IX travels posteriorly along the stylopharyngeus muscle and enters the space between the superior and middle pharyngeal constrictor muscle as the stylopharyngeus muscle does.

Posterior to cranial nerves IX, X, and XI, the upper portion of internal jugular vein exits the jugular fossa. Slightly medial to the jugular foramen, cranial nerve XII exits the hypoglossal canal and travels posterolaterally across the internal jugular vein. Anteromedially to the jugular foramen is the upper end of the internal carotid artery as it enters the posterior part of the carotid canal. It should be noted that the sympathetic trunk, including the superior cervical ganglion, is directly posterior to the internal carotid artery as it travels downwards on the lateral aspect of the pharyngeal constrictor muscles and merges to form the common carotid artery.

Examining from a lateral perspective, gaps between the pharyngeal constrictor muscles exist. These gaps serve as entry points for various structures. As mentioned above, superior to the superior constrictor muscle, the gap allows entry for the levator veli palatini muscles and auditory tube. Also mentioned above, the stylopharyngeus muscle, cranial nerve IX, and the stylohyoid ligament enter between the superior and middle pharyngeal constrictor muscles.

Continuing down the exterior pharyngeal wall, the gap between the middle and inferior pharyngeal constrictor muscles allow entry of the internal branch of the superior laryngeal nerve and the superior laryngeal artery. Lastly, inferior to the inferior constrictor muscle allows entry to the recurrent laryngeal nerve.

Interior of the Pharynx

The best way to examine the interior of the pharynx is either a sagittal cross-section or posteriorly after midline dissection of the external surface of the pharynx.

Nasal Part (Nasopharynx)

The nasopharynx is defined anatomically as the region superior to the soft palate that communicates with the nasal cavity through the choanae. Specifically, the superior border is defined as the pharyngeal fornix, a mucous membrane intimately layering the basal parts of the occipital and sphenoid bones. Laterally and posteriorly, the superior pharyngeal constrictor muscles and the pharyngobasilar fascia define the borders.

The inferior border of the nasopharynx is defined as the pharyngeal isthmus, an opening that leads into the oropharynx formed by the back of the soft palate and the posterior wall of the pharynx. The anterior border, in essence, does not exist since the nasopharynx communicates anteriorly with the nasal cavity. The most prominent feature of the nasopharynx is the pharyngeal ostium of the auditory tube—located posterolaterally from the choanae.

The ostium is surrounded by cartilage that produces a horseshoe elevation known as the torus tubarius. From the posterior aspect of the torus tubarius arises the salpingopharyngeal fold that contains the salpingopharyngeus muscle, which originates from the cartilaginous torus tubarius and blends with the palatopharyngeus muscle.

Posterior to the salpingopharyngeal fold exists a slit-like depression named the pharyngeal recess, also known as the fossa of Rosenmuller. Additionally, the salpingopalatine fold arises from the anterior border of the torus tubarius. Inferior to the torus is another fold named the torus levatorius, formed by the levator veli palatini muscle.

In the posterior, superior part of the nasopharynx and posterior portion of the auditory tube, lymphoid aggregates known as the pharyngeal tonsil and the tubal tonsil, its frequent extension, reside. When inflamed, these tonsils are referred to as adenoids and can cause obstruction of the nasopharynx, resulting in difficulty breathing.

Oral Part (Oropharynx)

The oropharynx is the middle part of the pharynx directly below the soft palate that communicates anteriorly with the oral cavity proper by the isthmus of the fauces, also known as the oropharyngeal isthmus. Specifically, the oropharyngeal isthmus is bound superiorly by the soft palate, laterally by the palatoglossal arches, and inferiorly by the posterior third of the tongue.

The oropharynx is defined anatomically by certain boundaries as well. It is bound superiorly by the undersurface of the soft palate and inferiorly by the root of the posterior tongue and the epiglottis. Anteriorly, the oropharynx is well demarcated from the oral cavity proper by the oropharyngeal isthmus mentioned above. The posterior root of the tongue exhibits numerous follicles that contain lymphatic tissue, which are known collectively as lingual tonsils. In close proximity, the lingual surface of the epiglottis curves anteriorly and is attached to the posterior tongue at the midline and lateral edges, forming the median and lateral glossoepiglottic folds. The depressions created between the median and lateral glossoepiglottic folds are termed epiglottic valleculae.

The most prominent feature of the oropharynx is the two folds that are termed the pillars of the fauces, the palatoglossal arch and the palatopharyngeal arch. The palatoglossal arch contains the palatoglossus muscle and travels anteroinferiorly from the soft palate to the lateral aspect of the tongue.

Posterior to the palatoglossal arch, the palatopharyngeal arch that contains the palatopharyngeus muscle travels posteroinferiorly from the soft palate to the lateral part of the pharynx. Because of the different insertion points and direction the arches travel within the oropharynx, they create a triangular space known as the tonsillar fossa, which contains lymphoid tissue known as the palatine tonsil. The arches are used as anatomic landmarks for the purposes of palatine tonsillar evaluation, manipulation, and surgery.

Laryngeal Part (Laryngopharynx)

The laryngopharynx is the lowest third of the interior pharynx and communicates with the larynx through the inlet of the larynx, also known as the aditus. Specifically, its superior border is the epiglottis and oropharynx and its inferior border is the posterior surface of the cricoid cartilage of the larynx.

At the level of the epiglottis, the laryngopharynx is wide but narrows at the level of the cricoid cartilage as it merges with the esophagus. At the level of the cricoid cartilage, the laryngopharynx extends to the lateral aspects of the larynx. At this location, the laryngopharynx is medially bordered by the aryepiglottic folds and laterally bordered by the thyroid cartilage, forming a sinus known as the piriform recess.

Innervation of the Pharynx

Most sensory innervation of the pharynx is derived from the glossopharyngeal nerve, specifically the pharyngeal and tonsillar branches (cranial nerve IX), except for the anterior part of the nasopharynx, which is innervated by a branch of the maxillary nerve (cranial nerve V2) called the pharyngeal nerve.

The pharyngeal nerve, as alluded to previously, is a small sensory nerve that passes through the palatovaginal or pharyngeal canal with its accompanying arterial branch (pharyngeal artery branching from the maxillary artery), which is between the sphenoid and palatine bone and supplies sensation to parts of the nasopharynx and the auditory tube. [4]

The pharyngeal branch of cranial nerve IX arises prior to the glossopharyngeal nerve traveling intimately with the stylopharyngeus muscle. The pharyngeal branch then merges with the pharyngeal branch of the vagus nerve (cranial nerve X), as well as the cranial part of the spinal accessory nerve, which then proceeds to the pharyngeal plexus located within the external fascia of the pharynx. Although the pharyngeal branch provides most of the sensory innervation, the tonsillar branch of the glossopharyngeal nerve directly supplies the oropharyngeal isthmus as it communicates with the lesser palatine nerve (from cranial nerve V2).

Additionally, the lesser palatine branch of the maxillary nerve provides the sensory fibers for the soft palate. It is noteworthy to mention that both the pharyngeal and lesser palatine branches arise from the maxillary division of the trigeminal nerve in the pterygopalatine fossa.

As mentioned earlier, the pharynx consists of 6 major muscles: the superior pharyngeal constrictor, middle pharyngeal constrictor, inferior pharyngeal constrictor stylopharyngeus, salpingopharyngeus, and palatopharyngeus. All derive motor input from pharyngeal and superior laryngeal branches of the vagus nerve (cranial nerve X) through the pharyngeal plexus, except the stylopharyngeus. Instead, the stylopharyngeus muscle derives motor innervation from the glossopharyngeal nerve (cranial nerve IX) from fibers of the nucleus ambiguus.

Vasculature

The pharynx receives its blood supply from a variety of sources, depending on anatomical location. The upper part of the pharynx receives blood from the pharyngeal branch of the ascending pharyngeal artery and descending branches of the lesser palatine arteries. The lower part of the pharynx receives blood supply from inferior thyroid artery and superior thyroid artery. The rest of the pharynx receives blood from the ascending palatine and tonsillar branches of the facial artery as well as from the maxillary artery.

Table 1 specifies the major muscles and their respective blood supplies.

Table 1. Major Muscles of the Pharynx and Their Respective Blood Supplies (Open Table in a new window)

Muscle Blood Supply
Superior pharyngeal constrictor Ascending pharyngeal artery (pharyngeal branch)



Facial artery (tonsillar branch)



Middle pharyngeal constrictor Ascending pharyngeal artery (pharyngeal branch)



Facial artery (tonsillar branch)



Inferior pharyngeal constrictor Ascending pharyngeal artery (pharyngeal branch)



Inferior thyroid artery (muscular branches)



Palatopharyngeus Facial artery (ascending palatine branch)



Maxillary artery (descending palatine branch)



Ascending pharyngeal artery (pharyngeal branch)



Salpingopharyngeus Same as palatopharyngeus:



Facial artery (ascending palatine branch)



Maxillary artery (descending palatine branch)



Ascending pharyngeal artery (pharyngeal branch)



Stylopharyngeus Ascending pharyngeal artery (pharyngeal branch)

 

Pharyngeal veins drain into the pharyngeal plexus, which is located on the posterior wall of the pharynx. The pharyngeal plexus can drain either into the internal jugular vein or brachiocephalic vein via the inferior thyroid vein.

Previous
Next:

Microscopic Anatomy

The walls of nasopharynx, oropharynx, and laryngopharynx are composed of four layers. From internal (luminal side) to external, the layers are the mucosa, submucosa, muscle layer, and fibrosa. For the purposes of simplicity, the nasopharynx is discussed in detail by itself. The oropharynx and laryngopharynx are discussed as a group because the microanatomy of the two is almost identical.

Nasopharynx

The mucosal layer consists of epithelium and lamina propria. There is significant debate regarding the epithelium of the nasopharynx—whether it is predominantly respiratory epithelium or stratified squamous epithelium and where the anatomical divisions between these two types of epithelium occurred within the nasopharynx. Most literature describes that, as a whole, the nasopharynx consists of 40% respiratory epithelium and 60% stratified squamous epithelium.

The respiratory epithelium, ciliated columnar, is predominantly found directly posterior to the choanae and on the roof of the posterior wall. On the other hand, stratified squamous epithelium predominates in the anterior, posterior, and lateral portions of the lower pharyngeal walls. The remaining portion of the nasopharynx that includes the posterior wall of the mid-nasopharynx is stated to have alternating patterns of squamous and ciliated columnar epithelium sometimes called intermediate epithelium. This kind of epithelium is usually concentrated near the junction of the nasopharynx and oropharynx. This alternating pattern can also be seen with the pharyngeal tonsil.

The lamina propria contains copious amounts of elastic tissue. The submucosa contains simple branched tubuloalveolar glands that are typically seromucous (mixed), producing mainly mucin. These are predominantly found near the auditory tube. Additionally, the submucosa contains lymphatic tissue. The lymphatic nodule aggregate in the posterosuperior nasopharyngeal wall forms the pharyngeal tonsil. The muscular layer consists of skeletal muscle. Lastly, the fibrosa is a thin layer of fibrous connective tissue.

Oropharynx and Laryngopharynx

The mucosal layer of the oropharynx and laryngopharynx are both lined with stratified squamous epithelium that is typically nonkeratinized. However, in autopsies of patients, stratified squamous keratinized biopsies of the oropharynx and laryngopharynx have been identified. One hypothesis is that these regions may potentially secrete keratin as a defense mechanism after years of epithelium irritation and damage. Similar to the nasopharynx, the oropharynx and laryngopharynx contain lymphoid aggregates in the submucosal and seromucous glands.

Previous
Next:

Pathophysiologic Variants

Inflammation

The most common inflammatory processes of the nasopharynx are pharyngitis and tonsillitis. Although infectious bacteria can be the cause of pharyngitis and tonsillitis, the most common etiology still remains viral upper respiratory infections. The most implicated viral pathogens are echoviruses, rhinoviruses, adenovirus, and respiratory syncytial viruses.

A typical visual presentation of viral etiology would involve erythema, edema of the nasopharynx mucosa, and enlargement of lymph tissue. As mentioned above, pharyngitis and tonsillitis can also have a bacterial etiology—namely beta-hemolytic streptococci and Staphylococcus aureus. A typical presentation of bacterial etiology would involve erythema of the nasopharynx mucosa along with an exudative membrane. Because bacterial pharyngitis and tonsillitis can be easily treated with antibiotics, the only major complications are the infections’ sequelae without proper treatment: rheumatic fever and glomerulonephritis mostly arising from streptococcal pharyngitis. [5]

Tumors

Nasopharyngeal Angiofibroma

Nasopharyngeal angiofibroma is an extremely vascularized tumor that typically occurs in adolescent males. It has a tendency to bleed during surgery. It can be seen as a smooth mass mostly in the posterior nasopharynx. It is a benign tumor that is very locally aggressive. Most patients present with nasal obstruction and epistaxis. Biopsy is particular dangerous since the tumor is so vascular. Angiofibromas have a tendency to bleed during surgery, which is why it is imperative to keep the patient hypotense to reduce the risk of bleeding. The tumor can also be embolized preoperatively to reduce bleeding even further. [6]

Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma is a tumor that epidemiologically has distinct geographic associations and can take three distinct patterns: keratinizing squamous cell carcinoma (25%), nonkeratinizing squamous cell carcinoma (15%), and undifferentiated carcinomas (60%). The pharyngeal recess is the most common anatomical location for the nasopharyngeal carcinoma.

The factors that affect the geographic distribution are heredity, age, and infection with Epstein-Barr virus. In Africa, it is a childhood cancer; in southern China, it is common in adults but rare in children; and in the United States, it is rare in both adults and children. Human papillomavirus infection may also be associated with the development of nasopharyngeal carcinoma. [7, 8]

Laryngopharynx (Hypopharynx) Squamous Cell Carcinoma

The most common tumor of the laryngopharynx is a squamous cell carcinoma (95%). It typically presents in males around the sixth and seventh decades of life. Although it can occur in the postcricoid region or posterior wall, most occur within the piriform recess. The greatest predisposing factors are alcohol and tobacco use. [9]

Parkinson Disease

The pharynx has a very important role in swallowing, and interruption of muscle innervation can cause dysphagia or even aspiration. The most common cause of death in Parkinson disease is aspiration pneumonia, and some information suggests the pharyngeal plexus can be affected by the parkinsonian pathology, causing impaired nerve sensation and impaired swallowing reflex, leading to aspiration. [10]

Obstructive Sleep Apnea

Sleep apnea can be attributed to enlarged lymphoid tissue or redundant soft palate, but it can also be attributed to oropharyngeal collapse from a number of etiologies such as smoking and obesity. Smoking increases the edematous nature of the mucosa, especially the uvular mucosa, causing a decrease in the airway diameter. Obesity and fat deposition near the pharynx, as well as edema from smoking, causes a decrease in longitudinal traction and wall tension, leading to easier collapse. There is also a role of relaxation of the pharyngeal musculature itself during sleep, during which even a minimally collapsed airway fails to respond to the appropriate mechanical load. [11, 12, 13]

Previous