Tonsil and Adenoid Anatomy

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The palatine tonsils are dense compact bodies of lymphoid tissue that are located in the lateral wall of the oropharynx, bounded by the palatoglossus muscle anteriorly and the palatopharyngeus and superior constrictor muscles posteriorly and laterally. ^[1]

The adenoid is a median mass of mucosa-associated lymphoid tissue. It is situated in the roof and posterior wall of the nasopharynx. ^[2] The adenoid was first described in 1868 by the Danish physician Meyer in his paper “Adenoid Vegetations in the Nasopharyngeal Cavity.” ^[3]

Both tonsils and adenoid are part of the Waldeyer ring, which is a ring of lymphoid tissue found in the pharynx. The lymphoid tissue in this ring provides defense against pathogens. The Waldeyer ring is involved in the production of immunoglobulins and the development of both B cells and T cells. ^[1]

The tonsils begin developing early in the third month of fetal life. They arise from the endoderm lining, the second pharyngeal pouch, and the mesoderm of the second pharyngeal membrane and adjacent regions of the first and second arches. The epithelium of the second pouch proliferates to form solid endodermal buds, growing into the underlying mesoderm; these buds give rise to tonsillar stroma. Central cells of the buds later die and slough, converting the solid buds into hollow tonsillar crypts, which are infiltrated by lymphoid tissue. ^[4]

Both right and left tonsils form part of the circumpharyngeal lymphoid ring. The size of the tonsil varies according to the age, individuality, and pathologic status. At the fifth or sixth year of life, the tonsils rapidly increase in size, reaching their maximum size at puberty. At puberty, the tonsils measure 20-25 mm in vertical and 10-15 mm in transverse diameters. ^[2]

Anatomic relations

Anteriorly and posteriorly, the tonsil is related to the palatoglossus and palatopharyngeus muscles, lying within their respective folds. A few fibers of the palatopharyngeus are found in the tonsil bed and are attached to the lower part of the capsule along with the fibers of the palatoglossus. Superiorly, the tonsil extends into the edge of the soft palate; inferiorly, the tonsillar capsule is firmly attached to the side of the tongue (see the images and videos below). ^[5]

On the lateral surface, the tonsil has a thin distinct capsule, which is formed from condensation of pharyngobasilar fascia. This fascia extends into the tonsil itself, forming septa, which allow passage of nerves and vessels. ^[1]

Deep to the pharyngobasilar fascia, in the upper part of the fossa, is the superior constrictor ; below it is the styloglossus passing forward into the tongue. The buccopharyngeal fascia is situated lateral to the superior constrictor . The glossopharyngeal nerve and stylohyoid ligament pass obliquely downward and forwards beneath the lower edge of the superior constrictor in the lower part of the tonsillar fossa. The paratonsillar vein descends from the soft palate across the lateral aspect of the capsule of the tonsil before piercing the pharyngeal wall to join the pharyngeal plexus. ^[5]

The medial free surface projects into the oropharynx and is covered by a thin layer of stratified squamous epithelium, which extends from the surface deep into the tonsil, forming crypts. ^[1] The medial surface has a pitted appearance; each tonsil has 10-20 pits. The openings of the crypts are fissurelike, and the walls of the crypt lumina are collapsed and in contact with each other. ^[2]

The mouth of the supratonsillar fossa (intratonsillar cleft) opens in the upper part of the medial surface of the tonsil. The mouth of the cleft is semilunar, curving parallel to the convex dorsum of the tongue in the parasagittal plane. ^[2] It is thought to represent a persistent part of the ventral portion of the second pharyngeal pouch. ^[5]

A triangular fold of mucus membrane is present during fetal life, extending from the lower part of the palatoglossal fold to the anteroinferior part of the tonsil. During childhood, this fold is invaded by lymphoid tissue and is incorporated into the tonsil. A semilunar fold of mucus membrane is present between the palatopharyngeal arch and the upper pole of the tonsil. This fold separates the upper pole of the tonsil from the base of the uvula. A tonsillolingual sulcus separates the tonsils from the base of the tongue. ^[5]

Vascular supply

The arterial supply of the tonsils is derived from the following arteries:

1. Tonsillar artery

2. Ascending pharyngeal artery

3. Tonsillar branch of the facial artery

4. Dorsal lingual branch of the lingual artery

5. Ascending palatine branches of the facial artery

Venous blood drains through a peritonsillar plexus. The plexus drains into the lingual and pharyngeal veins, which in turn drain into the internal jugular vein. ^[3]

Nerve supply

The tonsils are innervated via tonsillar branches of the maxillary nerve and the glossopharyngeal nerve. ^[2]

Lymphatic supply

Tonsils do not posses afferent lymphatics. Efferent lymphatics drain directly to the jugulodigastric nodes and upper deep cervical nymph nodes and indirectly through the retropharyngeal lymph nodes. ^[2]

The adenoid develops as a midline structure by fusion of 2 lateral primordia that become visible during early fetal life. ^[3] Lymphoid tissue can be identified at 4-6 weeks of gestation, lying within the mucous membrane of the roof and the posterior wall of the nasopharynx. ^[6] The adenoid is fully developed during the seventh month of gestation and continues to grow until the fifth year of life. ^[3] The lymphoid tissue of the adenoid may extend to the fossa of Rosenmuller and to the eustachian tube orifice as Gerlach’s tonsil. ^[6]

A fully grown adenoid is shaped like a truncated pyramid with its base at the junction of the roof and the posterior wall of the nasopharynx and its apex pointing toward the nasal septum (see the image and the video below). ^[2] It does not contain crypts and is not surrounded by a distinct capsule. The adenoid is formed by vertical folds of respiratory epithelium from which Arey glands extend. ^[1] These folds radiate forward and laterally from a median blind recess, the pharyngeal bursa (bursa of Luschka). ^[2]

Vascular supply

The arterial supply of the adenoid is derived from the following arteries:

1. Ascending pharyngeal artery

2. Ascending palatine artery

3. Tonsillar branch of the facial artery

4. Pharyngeal branch of the maxillary artery

5. Artery of the pterygoid canal

6. Basisphenoid artery

Venous drainage is to the pharyngeal plexus, which communicates with the pterygoid plexus and then drains into the internal jugular and facial veins. ^{[1, 2, 3]}

Nerve supply

The adenoid receives its nerve supply from the pharyngeal plexus.

Lymphatic supply

The lymphatic of the adenoid drains into the retropharyngeal and pharyngomaxillary space lymph nodes.

The tonsil consists of a mass of lymphoid follicles supported by a connective tissue framework. The lymphocytes are dense in the center of each nodule, an area commonly referred to as the germinal center (because multiplication of lymphocytes takes place at this center). The tonsillar crypts penetrate nearly the whole thickness of the tonsil and distinguish it histologically from other lymphoid organs. ^[5] The luminal surface of the tonsil is covered with nonkeratinizing stratified squamous epithelium, and it is continuous with that of the remainder of the oropharynx. ^{[1, 2]}

The adenoid is covered by a pseudostratified ciliated columnar epithelium that is plicated to form numerous surface folds. ^[3] The nasopharyngeal epithelium lines a series of mucosal folds, around which the lymphoid parenchyma is organized into follicles and is subdivided into 4 lobes by connective tissue septa (see the image below). Seromucous glands lie within the connective tissue, and their ducts extend through the parenchyma and reach the nasopharyngeal surface. ^[1]

The tonsil is more active in childhood and gradually becomes smaller during puberty. Its appearance may give a misleading estimate of its size. Some tonsils appear to lie mostly on the surface of the throat, with a shallow tonsillar fossa; others appear to be mostly buried in a deep tonsillar fossa. ^[5]

A median fold may pass forward from the pharyngeal bursa toward the nasal septum, or a fissure may extend forward from the bursa, dividing the adenoid into 2 parts, in a reflection of its paired developmental origin. ^[2]

Tonsillar involution begins at puberty; by old age, only a little tonsillar tissue remains. ^[2] Tonsillar crypts may contain desquamated epithelial debris and cells. Usually, this debris is cleared from the crypts. Rarely, the debris may remain in the crypts and become hardened and yellow in appearance. ^[5]

The adenoid grows rapidly after birth and usually undergoes a degree of involution and atrophy from the age of 8-10 years. It is rarely seen in adults. ^{[1, 2, 3]}

The lateral surface of the tonsil is covered by fibrous capsule, and it is separated from the oropharynx by loose areolar tissue. This separation makes dissection of tonsil easy during tonsillectomy. ^[5]

The bed of the nasopharyngeal tonsil is supplied by the basisphenoid artery; this is a possible source of persistent postadenoidectomy hemorrhage in some patients. ^[2]

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Susan S, Harold E, Jermiah CH, David J, Andrew W. Pharynx (chapter 35). Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 39th ed. Philadelphia: Elsevier; 2005. 619-631.

Wiatrak BJ, Woolley AL. Pharyngitis and adenotonsillar disease. Cummings CW, Fredrickson JM , Harker LA, Crause CJ, Schuller DE, Richardson MA. Otolaryngology Head and Neck Surgery. 3rd ed. London: Mosby; 1998. 188-215.

William JL, Lawrence SS, Steven P, William JS. Human Embryology. 3rd ed. Philadelphia: Elsevier; 2001. 375-376.

Beasley P. Anatomy of the pharynx and oesophagus. Kerr AG, Gleeson M. Scott-Brown’s Otorhinolaryngology. 6th ed. India: Butterworth-Heinemann publications; 1997. 1: 1/10/1 to 1/10/40.

Robb PJ. The adenoid and adenoidectomy. Gleeson M. Scott-Brown’s Otorhinolaryngology, Head and Neck Surgery. 7th ed. London: Hodder Arnold; 2008. 1: 1094-1101.

B Viswanatha, DO, MBBS, PhD, MS, FACS, FRCS(Glasg) Professor of Otolaryngology (ENT), Sri Venkateshwara ENT Institute, Victoria Hospital, Bangalore Medical College and Research Institute, India

B Viswanatha, DO, MBBS, PhD, MS, FACS, FRCS(Glasg) is a member of the following medical societies: Association of Otolaryngologists of India, Indian Medical Association, Indian Society of Otology

Disclosure: Nothing to disclose.

Arlen D Meyers, MD, MBA Professor of Otolaryngology, Dentistry, and Engineering, University of Colorado School of Medicine

Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, American Head and Neck Society

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Cerescan;RxRevu;Cliexa;Preacute Population Health Management;The Physicians Edge<br/>Received income in an amount equal to or greater than $250 from: The Physicians Edge, Cliexa<br/> Received stock from RxRevu; Received ownership interest from Cerescan for consulting; for: Rxblockchain;Bridge Health.

The authors would like to thank their teachers and family members for their encouragement.

Medscape Reference thanks Ravindhra G Elluru, MD, PhD, Associate Professor, Department of Otolaryngology Head and Neck Surgery, University of Cincinnati College of Medicine; Pediatric Otolaryngologist, Department of Otolaryngology, Cincinnati Children’s Hospital Medical Center, for the video contributions to this article.

Tonsil and Adenoid Anatomy

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