Anatomy of Inner Waldayer'sring

ByDr. T. Balasubramanian

Introduction:A ring of lympnoid tissue surround the naso pharynx and oro pharynx. These lymphoid tissueare collectively known as the waldayer's ring. Waldayer's ring has two components, namely theinner and outer rings. The cervical lymph nodes constitute the outer ring.The inner Waldayer's ring is formed by:1. Adenoid at the roof of nasopharynx2. Tubal tonsil of Gerlac surrounding the pharyngeal ends of eustachean tube3. Palatine tonsils on either side of oropharynx4. Lingual tonsil5. Lymphoid tissue in the submucosal plane of posterior pharyngeal wall

At this juncture it should be borne in mind that all these components are interconnected in thesubmucosal plane. If one component of the inner ring is inflammed, it goes without saying theother components also would be affected in varying degrees.Role played by the components of Waldayer's ring :Components of Waldayer's ring serve as antigen sampling centre for the immune system of thebody. Antigen from the inspired air is sampled by adenoid and tubal tonsils, processed andpresented to the immune system.The processed antigen are presented to B lymphocytes sothat immunoglobulins against the antigen can be secreted. To increase the efficiency of antigentrapping the surface of adenoid has numerous furrows. These furrows not only increases thesurface area of adenoid but also increases the efficiency of antigen sampling function ofadenoid. Similarly palatine tonsils sample ingested antigen. The surface area of tonsil isincreased by the presence of crypts. Each palatine tonsil has about 20 crypts. The largest ofthe crypt is known as crypta magna. The largest crypt of palatine tonsil is also known assupratonsillar cleft. This is a remnant of ventral portion of second pharyngeal pouch. Thesecrypts increase the surface area of palatine tonsil thereby increasing its antigen trapping ability.

Diagram showing components of Waldayer's ring

Anatomy of Palatine tonsilEmbryology:Developmentally this largest member of Waldayer's ring develops from the ventral portion ofsecond pharyngeal pouch. This portion of the second pharyngeal pouch has been ideallychristened as sinus tonsillaris. Remnants of this portion of the second pharyngeal pouch isseen in the fully developed tonsillar tissue as supra tonsillar cleft.

Diagram showing development of palatine tonsil

Position:Palatine tonsils are lodged in the tonsillar fossa on edither side of oropharynx. The tonsillarfossa is bounded anteriorly by anterior pillar (which is a mucosal fold raised by the underlyingpalatoglossus muscle) and posteriorly by the posterior pillar (mucosal fold raised bypalatopharyngeus muscle).The outer wall of palatine tonsil is encapsulated. This capsule is formed by condensation ofpharyngobasilar fascia. This fascia is also known to extend into the tonsillar tissue to formsepta that conducts blood vessels and nerves into the tonsillar tissue. Deep to this capsulartissue lie the superior constrictor muscle. Lateral to this muscle is the buccopharyngealfascia.

Figure showing anatomical relationships of palatine tonsil

In the lower part of tonsillar fossa the glossopharyngeal nerve and stylohyoid ligament passdownwards and forwards beneath the lower edge of superior constrictor. All these structurescollectively take part in the formation of tonsillar bed.Structures forming the tonsillar bed include:1. Superior constrictor of pharynx2. Pterygomandibular raphe ­ here superior constrictor and buccinator are inserted3. Middle constrictor of pharynx4. Tonsillar branch of facial artery5. Glossopharyngeal nerve6. Stylohyoid ligamentMedial surface of tonsil is free and it faces the oropharynx. This surface is covered with non­keratinizing stratified squamous epithelium which is the epithelium that lines the oral cavity. Atriangular fold of mucous membrane extends back from the palatoglossal fold to cover theantero­inferior portion of the tonsil. This fold of mucous membrane is known as plicatriangularis. In childhood this fold of mucous membrane is invaded by lymphoid tissue whichgets incorporated into the tonsil.A semilunar fold of mucous membrane passes from the upper aspect of palatopharyngealarch towards the upper pole of tonsil. This fold of mucous membrane known as plicasemilunaris separates the tonsillar tissue from uvula.

Figure showing plica semilunaris

Blood supply of palatine tonsil:1. Tonsillar branch of facial artery is the main supply. It enters the tonsil close to its lowerpole piercing the superior constrictor muscle just above the styloglossus muscle.2. Dorsal lingual branches from lingual artery3. Ascending palatine branch of facial artery4. Ascending pharyngeal branch of external carotid artery

Venous drainage from tonsil is through the paratonsillar vein. This vein may join the facialvein or pharyngeal plexus after piercing the superior constrictor. Injury to this vein is thecommonest cause of venous bleeding following tonsillectomy.Palatine tonsils have only efferent lymphatics. These lymphatics pierce thebuccopharyngeal facia and pass to the upper deep cervical node especially thejugulodigastric group.Caution: Internal carotid artery lies 2.5 cms behind and lateral to the tonsil.Nerve supply to palatine tonsil:Glossopharyngeal nerve supplies the tonsil. During epidemics of polio it has beenpostulated that polio virus may reach the medulla of brain via this nerve causing bulbarpoliomyelitis. That is the reason why tonsillectomy is contraindicated during epidemics ofpolio.The sphenopalatine ganglion supplies the tonsil via the lesser palatine nerves.Histology of tonsil:Tonsil is made up of lymphoid follicles within a fine connective tissue matrix. Lymphocytesare closely packed over the periphery of the follicles. At the centre lymphocytes are lessclosely packed because multiplication of lymphocytes occur here, hence this area is knownas germinal centres. The medial surface of the tonsil is characterised by 15 ­ 20 openingsat irregular intervals. These openings lead to blind narrow recesses known as crypts.These crypts penetrate nearly the whole of the tonsillar tissue. The mucous membranecovering the tonsil is of non keratinizing stratified squamous type. This epithelium dipsinside to line the crypts. These crypts may contain desquamated epithelial debris. Thelargest of these crypts is known as crypta magna, which is present close to the superiorpole of tonsil.

Image showing histology of palatine tonsil

Immunology:Immunologically tonsils and adenoid are predominantly B cell organs. B lymphocytesconstitute nearly 60% of all lymphoid cell population while the T lymphocytes make up forthe rest 40%.Immunologically potent cells are found in 4 different zones of tonsil. These zones are:1. Reticular cell epithelium2. Extra follicular areas3. Mantle zone4. Germinal centre folliclesHuman tonsillar cells are immunologically most active between 4­10 years of age.Tonsillar involution begins after puberty resulting in a decrease in the ratio of T:B cells. Inpatients with inflammation of tonsils and adenoid there is sheading of immune cells andthese cells are eventually replaced by stratified squamous epithelium. These changesthus cause a reduction in the number of B cells leading on to a general reduction in thebody's immunity.

Figure showing immunoglobulin

Adenoid:This is a collection of lymphoid tissue in the mucous membrane overlying thebasisphenoid area. It is oblong shaped (more or less like a truncated pyramid). It virtuallyhangs from the roof of nasopharynx. The anterior edge of adenoid is vertical and lie inthe same plane as the post nasal aperture. Its posterior edge merges imperceptibly intothe posterior nasopharyngeal wall. Its lateral edges incline towards the midline. Itssurface is lined by ciliated columnar epithelium. The surface of adenoid is covered withfurrows. On touch adenoid feels like a bag of worms.

Endoscopic view of adenoid tissue

Blood supply of adenoid:Adenoid is supplied by1. Ascending pharyngeal artery2. Ascending palatine artery3. Pharyngeal branch of internal maxillary artery4. Artery of pterygoid canal5. Contributions from branches of tonsillar branch of facial artery

Venous drainage of adenoid is via the pharyngeal plexus which in turn drain into theinternal jugular vein.Adenoid enlargement causes a peculiar type of face known as adenoid facies. It ischaracterised by:1. Elongated face2. Pinched nostrils3. Open mouth4. High arched palate5. Shortened upper lip6. Vacant idiotic look.

Xray lateral view of skull showing enlarged adenoid

Adenoid Tonsil

Unencapsulated Encapsulated

Single Two in number

Has furrows Has crypts

Lined by ciliated columnar cells Lined by squamous cells

Present in nasopharynx Present in oropharynx

Has efferent and afferentlymphatics

Has efferent lymphatics only