There are 2 palatine tonsils (normally referred to as tonsils). Every tonsil is situated in the triangular fossa (tonsillar fossa) of the lateral wall of the oropharynx between the anterior and posterior columns of fauces and is an almond shaped mass of lymphoid tissue. The posterior column is composed by palatopharyngeal arch and anterior column is composed by palatoglossal arch.
The genuine size of tonsil is a lot bigger than it seems on oropharyngeal evaluation because parts of tonsil go upwards into the soft palate, downwards in the base of the tongue and anteriorly underneath the palatoglossal arch.
Borders of The Tonsillar Fossa/Sinus
Anterior: Palatoglossal arch consisting of palatoglossus muscle.
Posterior: Palatopharyngeal arch comprising palato pharyngeus muscle.
Apex: Soft palate, where both arches meet.
Base: Dorsal surface of the posterior one-third of the tongue.
Lateral wall(or tonsillar bed): Superior constrictor muscle (primarily).
It’s created from inside outwards by:
- Pharyngobasilar fascia,
- Superior constrictor muscle and
- Buccopharyngeal fascia.
The tonsil presents the following external features:
It’s free and bulges into the oropharynx. It’s lined by non-keratinized stratified squamous epithelium, which dips into the substance of tonsil creating crypts. The number of tonsillar crypts change from 12 to 15 and their openings can be viewed on the medial surface. 1 of the crypts situated near the upper part of the tonsil is extremely large and deep. It’s referred to as crypta magna or intratonsillar cleft and symbolizes the remnant of the second pharyngeal pouch. The crypts might be full of cheesy material being composed of epithelial cells, bacteria and food debris.
It’s covered by a well defined fibrous tissue, which creates the tonsillar hemicapsule. Between the capsule and the bed of tonsil is the loose areolar tissue (peritonsillar space), making it simple to dissect the tonsil in this plane during tonsillectomy. It’s also the site of collection of pus in peritonsillar abscess.
The superior constrictor splits this surface from these structures:
- Facial artery and 2 of its branches, the ascending palatine and tonsillar.
- Styloglossus muscle and glossopharyngeal nerve.
- Styloid process (when elongated).
- Angle of mandible and medial pterygoid muscle.
- Submandibular salivary gland
- The internal carotid artery is all about 2.5 cm posterolateral to the tonsil.
It enters underneath the palatoglossal arch.
It enters underneath thepalatopharyngeal arch.
It goes upward into the soft palate. Its medial surface is covered by a semilunar fold stretching between the anterior and posterior columns enclosing a potential space named supratonsillar fossa.
It’s connected to the tongue by a band of fibrous tissue termed suspensory ligament of the tonsil.
A triangular fold of mucous membrane goes from anterior column to the anteroinferior part of the tonsil. It encloses a potential space termed anterior tonsillar space.
The tonsil is divided from the tongue by a sulcus termed tonsillolingual sulcus.
Surface anatomy: An oval area 1.25 cm above and in front of the angle of the mandible, indicated in the parotid region of face suggests the location of tonsil on the surface.
Arterial Supply of The Tonsil
The following arteries supply the tonsil:
- Tonsillar branch of facial artery (it’s the main artery and enters the lower pole of the tonsil by piercing the superior constrictor).
- Dorsalis linguae branches of lingual artery.
- Ascending palatine, a branch of facial artery.
- Ascending pharyngeal, a branch of external carotid artery.
- Greater palatine (descending palatine), a branch of maxillary artery.
Venous Drainage of the Tonsil
The veins from tonsil drain into paratonsillar vein. The paratonsillar vein descends from the soft palate across the lateral aspect of the tonsillar capsule and pierces the superior constrictor to drain into pharyngeal venous plexus.
Lymphatic Drainage of the Tonsil
The lymphatics of tonsil pierce the superior constrictor and drain into the upper deep cervical lymph nodes, especially the jugulodigastric lymph node. It’s frequently referred to as tonsillar lymph node because it’s mostly enlarged in infection of the tonsil (tonsillitis). The tonsillar lymph node lies below the angle of the mandible.
Nerve Supply of the Tonsil
Palatine tonsil is supplied by the glossopharyngeal nerve and lesser palatine branches of the sphenopalatine ganglion.
The tonsils are the common sites of acute infection particularly in school-going kids. It might impact adults also. This condition is named acute tonsillitis.
It’s mainly viewed in viral infection. It’s uncommon in babies and men above 50 years old.
Acute Follicular Tonsillitis
In this state, the infection spreads into crypts, which become filled up with purulent material presenting at the openings of crypts as yellowish spots.
Bleeding From Tonsillar Fossa after Tonsillectomy
Itmost usually takes place because of damage of paratonsillar vein. The blood clots ought to be removed to be able to assess bleeding. If not removed, they interfere together with the retraction of the vessel walls by preventing the contraction of the surrounding muscles. The postoperative edema of tonsillar bed after tonsillectomy can impact the glossopharyngeal nerve resulting in loss of sense in the posterior one-third of the tongue.
Histologically, the tonsil presents these features:
- Its oral surface is lined by stratified squamous non-keratinized epithelium, which dips into underlying tissues to create crypts.
- Presence of lymphatic nodules on the sides of the crypts
- Presence of mucous glands in the deeper plane
Development of the Tonsil
The tonsil grows in the region of 2nd pharyngeal pouch. The cells of endodermal lining of pouch proliferate and develop out as solid columns/buds into the surrounding mesenchyme. The central portions of these cell columns are canalized and create tonsillar clefts. The lymphoid cells from the surrounding mesenchyme pile up around the crypts and differentiate into lymphoid follicles. The remnant of 2nd pharyngeal pouch is viewed as supratonsillar/intratonsillar cleft in the upper pole of the tonsil.