Palatine tonsil

The palatine tonsil is an ovoid mass of lymphoid tissue situated within the tonsillar fossa of the lateral wall of the oropharynx. It lies between the palatoglossal arch anteriorly and the palatopharyngeal arch posteriorly and forms an important component of the mucosaassociated lymphoid tissue (MALT) of the upper aerodigestive tract.

Supratonsillar fossa

The palatine tonsil occupies most of the tonsillar fossa, although it does not completely fill the space, leaving the supratonsillar fossa superiorly.

Medial surface of palatine tonsil

Medially, the tonsil projects into the oropharyngeal cavity and is covered by nonkeratinised stratified squamous epithelium continuous with the surrounding oropharyngeal mucosa. This medial surface contains numerous tonsillar crypts, which are deep epithelial invaginations that increase the surface area for antigen exposure and immune surveillance.

Lateral surface of palatine tonsil

Laterally, the palatine tonsil is enclosed by a fibrous capsule, which separates it from the superior constrictor muscle by loose areolar connective tissue forming the tonsillar bed. This plane is of major surgical importance during tonsillectomy. The lateral wall of the tonsillar fossa also contains important neurovascular structures closely related to the tonsil.

Arterial, venous, and lymphatic drainsage

The arterial supply of the palatine tonsil is rich and derived primarily from the tonsillar branch of the facial artery, with additional contributions from the ascending palatine, ascending pharyngeal, dorsal lingual, and greater palatine arteries.

Venous drainage occurs through the peritonsillar venous plexus into the pharyngeal venous plexus and facial vein.

Lymphatic drainage is mainly to the jugulodigastric lymph node, which commonly becomes enlarged in tonsillitis.

Innervation

Sensory innervation of the tonsillar region is chiefly provided by the glossopharyngeal nerve (CN IX). Because this nerve also supplies the middle ear, inflammation of the palatine tonsil may produce referred otalgia. Posterolateral to the tonsillar bed lies the internal carotid artery, approximately 2-2.5 cm from the tonsillar fossa.

Functional and clinical correlates

Functionally, the palatine tonsils contribute to immune defence by sampling inhaled and ingested pathogens and initiating lymphocytic immune responses. Together with the pharyngeal tonsil, lingual tonsil, and tubal lymphoid tissue, they form part of Waldeyers ring, a circular arrangement of lymphoid tissue guarding the entrances of the respiratory and gastrointestinal tracts.

Clinically, the palatine tonsils are commonly affected by acute and chronic tonsillitis. Recurrent infection may lead to enlargement, fibrosis, and accumulation of debris within the crypts, sometimes forming tonsilloliths. Their close vascular and neural relations make tonsillectomy a procedure of important anatomical significance.