Heinrich Wilhelm Gottfried von Waldeyer-Hartz first described the incomplete ring of lymphoid tissue, situated in the naso-oropharynx, in 1884. The ring acts as a first line of defence against microbes that enters the body via the nasal and oral routes. Waldeyer’s ring consists of four tonsillar structures (namely, the pharyngeal, tubal, palatine and lingual tonsils) as well as small collections of lymphatic tissue disbursed throughout the mucosal lining of the pharynx (mucosa-associated lymphoid tissue, MALT).
Pharyngeal Tonsil (Adenoids)
Situated superior-posteriorly to the torus tubaris (elevation around the pharyngeal opening of the Eustachian tube), in the roof of the nasopharynx, the pharyngeal tonsil is primarily responsible for ‘screening’ the air that enters through the nostrils. The pharyngeal tonsil is lined by pseudo-stratified ciliated columnar epithelium (respiratory epithelium). Unlike the other tonsils, there are no crypts (invaginations in the surface of the tonsil) present in this tonsil.
Blood supply to the pharyngeal tonsil arise from the:
- ascending pharyngeal and palatine arteries
- tonsillar branch of the facial artery
- pharyngeal branch of the maxillary artery
- artery of the pterygoid canal
- basosphenoid artery
Venous blood is returned to circulation via the pharyngeal plexus, which drains indirectly to the internal jugular veins (IJV). The pharyngeal tonsil is innervated by branches of the pharyngeal plexus and it achieves lymphatic drainage via the retropharyngeal and the pharyngomaxillary nodes.
Tubal Tonsils (Gerlach’s Tonsils)
The tubal tonsils are also located in the roof of the nasopharynx. They are bilateral and posterior to the torus tubaris, in the fossa of Rosenmüller (pharyngeal recess). Due to the relative closeness of the tubal tonsils to the torus tubaris, it is sometimes referred to as “the tonsils of the torus tubaris”. The term “tubal tonsils” is also synonymous with Eustachian tonsils and Gerlach’s tonsils.
These lymphoid structures are also lined by respiratory epithelium; additionally, crypts are present and infiltrated by lymphatic tissue. Gerlach’s tonsils receive arterial blood by branches of the sphenopalatine and the ascending pharyngeal arteries. Lymphatic drainage is achieved via the retropharyngeal and the deep cervical lymph nodes.
Palatine Tonsils (The Tonsils)
The palatine tonsils have been historically referred to as “the tonsils.” They are readily visible in the oropharynx when inflamed. These bilateral lymphoid aggregates each rest within a tonsillar cleft, bordered anteriorly by the palatoglossal arch and posteriorly by the palatopharyngeal arch. Unlike the adenoids, the palatine tonsils are covered by stratified non-keratinized squamous epithelium. They also have many invaginations to increase the probability of exposure of foreign antigens to the lymphatic tissue present in the crypts.
The tonsils receive arterial blood via the following arteries:
- ascending pharyngeal
- facial (tonsillar and ascending palatine branches)
- lingual (dorsal lingual branch)
The peritonsillar plexus (via the lingual and pharyngeal veins) return blood to the IJV. Innervation is via the tonsillar branch of glossopharyngeal nerve (CN IX) and the lesser palatine nerve, while the jugulodigastric and upper deep cervical lymph nodes are responsible for lymphatic drainage.
The numerous protrusions located at the posterior third of tongue - are collectively known as the lingual tonsils. They are also covered by stratified non-keratinized squamous epithelium. The dorsal lingual branch of the lingual artery and the lingual vein are responsible for the vascular supply and return of these lymphatic aggregates, while the glossopharyngeal nerve innervates them, along with the posterior of the tongue.
Mucosa-Associated Lymphoid Tissue (MALT)
Mucosa-associated lymphoid tissue (MALT) is found throughout the mucosal lining of the body. The nomenclature used to describe the lymphoid tissue adapts to the regional anatomy. For example, MALT in the gastrointestinal tract is referred to as gut-associated lymphatic tissue (GALT), while MALT in the respiratory airways, bronchus-associated lymphoid tissue (BALT). In the naso-oropharynx, MALT is found in the intratonsillary spaces (i.e., between the tonsillar aggregates).