Anatomy of pharynx

Introduction

• Pharynx is a conical fibromuscular tube forming upper part of the air and food passages.

• 12-14 cm long, extending from base of the skull to the lower border of cricoid cartilage where it becomes continuous with the oesophagus.

• The width of the pharynx is 3.5 cm at its base and this narrows to 1.5 cm at pharyngo-oesophageal junction.

Structure of Pharyngeal Wall

• From within outward it consists of four layers :– Mucous membrane– Pharyngeal aponeurosis– Muscular coat– Buccopharyngeal fascia

Killian’s dehiscence

• Inferior constrictor muscle has two parts ; thyropharyngeus with oblique fibres and cricopharyngeus with transverse fibres.

• Between this two parts exists a potential gap call Killian’s dehiscence.

• Also called ‘gateway of tears’ as perforation can occur at this site during oesophagoscopy.

• Also site for herniation of pharyngeal mucosa in cases of pharyngeal pouch.

Waldeyer’s ring

• Scattered throughout the pharynx in its subepithelial layer is the lymphoid tissue which is aggregated at place to form masses, collectively called Waldeyer’s ring. The masses are :– Nasopharyngeal tonsil (adenoids)– Palatine tonsils– Lingual tonsil– Tubal tonsils (in fossa of Rosenmuller)– Lateral pharyngeal bands– Nodules (in posterior pharyngeal wall)

Pharyngeal spaces

• There are two potential spaces in relation to the pharynx where abscesses can form.1. Retropharyngeal space, situated behind the

pharynx and extending from the base of skull to the bifurcation of trachea.

2. Parapharyngeal space, situated on the side of pharynx. It contains carotid vessels, jugular vein, last four cranial nerves and cervical sympathetic chain.

Division of the pharynx

• Anatomically, pharynx is divided into three parts :– Nasopharynx– Oropharynx– Hypopharynx or Laryngopharynx

Nasopharynx

• Is the uppermost part of the pharynx, also called epipharynx.

• It lies behind nasal cavities and extends from the base skull to the soft palate.

• Roof basisphenoid and basiocciput.• Posterior wall arch of atlas vertebra covered by

prevertebral muscle and fascia.• Floor soft palate anteriorly but is deficient posteriorly.

It is through this space --- nasopharyngeal isthmus, that the nasopharynx communicates with the oropharynx.

• Anterior wall posterior nasal apertures or choanae, separated from each other by the posterior border of nasal septum.

• Lateral wall each lateral wall presents the pharyngeal opening of eustachian tube situated 1.25cm behind the posterior end of inferior turbinate.

Nasopharyngeal tonsil (adenoids)

• It is subepithelial collection of lymphoid tissue at the junction of roof and posterior wall of nasopharynx and causes the overlying mucous membrane to be thrown into radiating folds.

• It increase in size up to the age of six years and then gradually atrophies.

Nasopharyngeal bursa

• It is an epithelial-lined median recess found within the adenoid mass and extends from pharyngeal mucosa to the periosteum of the basiocciput.

• It represents the attachment of notochord to the pharyngeal entoderm during embryonic life.

• When infected, it may be the cause of postnasal discharge or crusting.

• Sometimes an abscess can form in bursa (Thornwaldt’s disease)

Rathke’s pouch

• It is represented clinically by a dimple above adenoids and is reminiscent of the buccal mucosal invagination, to form the anterior lobe of pituitary.

• A craniopharyngioma may arise from it.

Tubal tonsil

• It is collection of subepithelial lymphoid tissue situated at the tubal elevation.

• It is continuous with adenoid tissue and forms a part of the Waldeyer’s ring. When enlarged due to infection, it causes eustachian tube occlusion.

Sinus of Morgagni

• It is space between the base of skull and upper free border of superior constrictor muscle.

• Through it enters :– The eustachian tube– The levator veli palatini– Tensor veli palatini– Ascending palatine artery – brance of facial artery

Passavant’s ridge

• It is a mucosal ridge raised by fibres of palatopharyngeus.

• It encircles the posterior and lateral walls of nasopharyngeal isthmus.

• Soft palate, during its contraction, makes firm contact with this ridge to cut off nasopharynx from the oropharynx during the deglutition or speech.

Epithelial lining of nasopharynx

• Functionally, nasopharynx is the posterior extension of nasal cavity.

• It is lined by pseudostratified ciliated columnar epithelium.

Lymphatic drainage

• Lymphatics of the nasopharynx, including those of the adenoids and pharyngeal end of eustachian tube, drain into upper deep cervical nodes either directly or indirectly through retropharyngeal and parapharyngeal lymph nodes.

• They also drain into spinal accessory chain of nodes in the posterior triangle of the neck.

• Lymphatics of the nasopharynx may also cross midline to drain into contralateral lymph node.

Functions of nasopharynx

• Acts as conduit for air• Ventilates the middle ear and equalises air

pressure on both sides of tympanic membrane• Cut of nasopharynx from oropharynx

(swallowing, vomitting, gagging, and speech)• Acts as resonating chamber during voice

production.• Acts as a drainage channel for the mucus

secreted by nasal and nasopharyngeal glands.

Oropharynx

• Extend from the plane of hard palate above to the plane of hyoid bone below.

• It lies opposite the oral cavity with which it communicates through oropharyngeal isthmus.

Boundaries of oropharynx

• Posterior wall related to retropharyngeal space and lies opposite the second and upper part of third cervical vertebrae.

• Anterior wall deficient above, where oropharynx communicates with the oral cavity, but below it presents :– Base of tounge– Lingual tonsils– Valleculae

• Lateral wall it presents :– Palatine tonsil– Anterior pillar– Posterior pillar

Lymphatic drainage

• Drain into upper jugular chain particularly the jugulodigastric (tonsillar) node.

• The soft palate, lateral and posterior pharyngeal walls and the base of tounge also drain into retropharyngeal and parapharyngeal nodes and from there to the jugulodigastric and posterior cervical group.

• The base of tounge may drain bilaterally.

Function of oropharynx

• As a conduit for passage of air and food• Helps in the pharyngeal phase of deglutition• Forms part of vocal tract for certain speech

sounds• Helps in appreciation of the taste• Provide local defence and immunity against

harmful intruders into the air and food passages

Hypopharynx (laryngopharynx)

• Lowest part of the pharynx and lies behind partly on the sides of the larynx.

• Its superior limit is the plane passing from the body of hyoid bone to the posterior pharyngeal wall, while the inferior limit is lower border of cricoid cartilage where hypopharynx becomes continuous with oesophagus.

• Lies opposite the 3rd, 4th, 5th, 6th cervical vertebrae.• Clinically, it is subdivided into three region :

– Pyriform sinus– Post-cricoid region– Posterior pharyngeal wall

Lymphatic drainage

• Pyriform sinus is richly supplied by lymphatic which exit through the thyrohyoid membrane and drain into the upper jugular chain

• Lymphatics of posterior wall terminate in the lateral pharyngeal or parapharyngeal nodes and then to the deep cervical lymph nodes

• Lymphatics of post-cricoid region also drain into the parapharyngeal nodes

Function of hypopharynx

• Pathway for air and food• Vocal tract for resonance of certain speech

sounds• Helps in deglutition