Anatomy, Head and Neck: Tonsils

Structure and Function

Like other lymphoid tissues, the tonsils contribute to immune defense by responding to infections and foreign antigens. The tonsils are strategically located at the junction of the respiratory and digestive tracts, where they initiate lymphokine and immunoglobulin production in response to inhaled or ingested pathogens.

Composed primarily of B-cell lymphoid tissue, the tonsils support mucosal secretory immunity. Specialized antigen-capturing cells, known as M cells, are present on the tonsillar surface and facilitate the uptake of microbial antigens. After antigen recognition, M cells stimulate resident T and B lymphocytes, initiating a localized immune response.[3] Activated B cells proliferate within the germinal centers of the tonsils, where memory B cells mature and are retained for future antigen exposure.[4] These B cells also produce immunoglobulin A, a key antibody in mucosal immunity. The cellular architecture of the tonsils closely resembles that of the Peyer patches in the gastrointestinal tract, which monitor and regulate intestinal bacterial populations.

The lymphoid tissue of the upper aerodigestive tract forms the Waldeyer ring, named for its noncontinuous, circumferential configuration in the oropharynx. This ring comprises the palatine, tubal, pharyngeal, and lingual tonsils (see Image. Tonsils and Throat).

The palatine tonsils are located in the posterior oral cavity, positioned bilaterally between the palatoglossal and palatopharyngeal arches within the tonsillar fossae (see Image. Oral Cavity and Palatine Tonsils). The free medial surfaces of these structures project into the oropharynx and are readily visible on clinical examination, while the lateral surfaces are covered by a fibrous hemicapsule. This capsule, along with intervening loose areolar tissue, separates the tonsils from the underlying superior pharyngeal constrictor muscle.

The lingual tonsil lies in the submucosa of the posterior 3rd of the tongue and consists of nodular lymphoid tissue forming the midline component of the Waldeyer ring at the oropharyngeal level. The pharyngeal tonsil is situated in the roof of the nasopharynx and consists of submucosal lymphoid tissue collections. The tubal tonsils, positioned laterally, surround the pharyngeal openings of the eustachian tubes and complete the ring.

Embryology

Tonsils are derivatives of the 2nd pharyngeal pouch.[5] These structures typically appear around the 4th or 5th month of gestation and continue to develop after birth, reaching full size at puberty. Tonsillar and adenoidal tissues exhibit peak immunologic activity between 4 and 12 years of age, followed by progressive atrophy beginning after puberty.[6][7]

Blood Supply and Lymphatics

The palatine tonsils lie along the lateral wall of the oropharynx, situated in a fossa between the anterior and posterior pillars. Five arteries contribute to the vascular supply of these structures. The primary source is the tonsillar branch of the facial artery, which enters at the lower pole. Additional arterial input arises from the ascending palatine, dorsal lingual, ascending pharyngeal, and lesser palatine arteries.[8] Venous drainage occurs mainly via the peritonsillar venous plexus, which empties into the pharyngeal and lingual veins before reaching the internal jugular vein.

Although the internal carotid artery does not directly supply the tonsils, it lies approximately 2.5 cm posterolateral to their position. Surgical manipulation in this region requires caution to prevent vascular injury.[9]

Nerves

The tonsils receive afferent innervation from the tonsillar plexus, which includes contributions from the trigeminal nerve (cranial nerve V) via the lesser palatine nerves, and the glossopharyngeal nerve (cranial nerve IX). The glossopharyngeal nerve extends beyond the tonsillar region to provide general sensory and taste innervation to the posterior 3rd of the tongue. Among the nerves in this region, the glossopharyngeal nerve is the most vulnerable to injury during tonsillectomy.

Surgical Considerations

Tonsillectomy

Surgical removal of the tonsils is referred to as a "tonsillectomy." Hemorrhagic tonsillitis constitutes an absolute indication for the procedure.[10] Relative indications include recurrent or chronic pharyngotonsillitis, peritonsillar abscess, and streptococcal pharyngitis.

Tonsillectomy involves dissection between the tonsillar capsule and the superior pharyngeal constrictor muscle, using either a “hot” or “cold” technique. The hot technique employs electrocautery for simultaneous dissection and hemostasis. In the cold technique, a superior incision is made through the mucosa, followed by blunt dissection to separate the tonsil from its bed. Final separation along the inferior pole is achieved using a snare. Cold dissection has demonstrated superior postoperative pain outcomes, while electrocautery is associated with reduced intraoperative blood loss. Newer modalities, such as carbon dioxide laser, ultrasound, and radiofrequency ablation, have been introduced to reduce postoperative morbidity, though further evidence is needed to support widespread adoption of these approaches.

Tonsillectomy complications are classified as acute, subacute, or delayed. Acute complications include airway obstruction due to edema, bleeding, and postobstructive pulmonary edema. Subacute complications include secondary hemorrhage, dehydration, and weight loss. Delayed or chronic complications include velopharyngeal insufficiency and nasopharyngeal stenosis.[11]

Adenotonsillectomy

Surgical removal of both the tonsils and adenoids is indicated in selected cases. This combined procedure is referred to as an "adenotonsillectomy." Absolute indications include adenotonsillar hypertrophy with obstructive sleep apnea, abnormal dentofacial development, and suspected or confirmed malignancy. Relative indications include dysphagia, speech disturbance, and chronic halitosis. Adenotonsillectomy does not result in any clinically significant immunologic deficiency. Contraindications include acute infection, anemia, coagulopathy (whether inherited or acquired), and elevated anesthetic risk.[12]

Clinical Significance

Tonsilloliths

Tonsilloliths, or tonsil stones, are whitish, malodorous concretions that form within the tonsillar crypts due to bacterial colonization and retained cellular debris. Most are asymptomatic but may cause halitosis, otalgia, or a foreign body sensation. Management is typically conservative, with patients advised to dislodge stones manually using cotton swabs. Surgical extraction may be necessary for large or symptomatic lesions. Mouth rinses and gargling can provide symptomatic relief, particularly in cases of halitosis.[13]

Bacterial Tonsillitis

Acute bacterial tonsillitis presents with an abrupt-onset sore throat, enlarged erythematous or exudative tonsils, halitosis, and tender cervical lymphadenopathy (see Image. Tonsillitis). Distinguishing bacterial from viral tonsillitis can be clinically challenging. Viral infections are managed supportively, while bacterial tonsillitis is treated with analgesics and antibiotics, typically amoxicillin or macrolides. Recurrent tonsillitis may warrant surgical intervention. The American Academy of Otolaryngology–Head and Neck Surgery recommends tonsillectomy in patients with 7 documented infections in a year, 5 per year for 2 consecutive years, or 3 per year for 3 consecutive years.[14] 

Adenotonsillar Disease

Adenotonsillar disease encompasses recurrent infections of the tonsils and adenoids. Patients may present with either acute or chronic adenoiditis. Clinical distinction is often difficult because symptoms frequently overlap with those of viral or bacterial upper respiratory tract infections. Adenoiditis typically presents with fever, purulent nasal discharge, and nasal obstruction and is frequently accompanied by otalgia. Group A β-hemolytic Streptococcus (Streptococcus pyogenes) is a common bacterial cause of acute tonsillitis. Chronic inflammation may lead to hypertrophy of both the tonsils and adenoids. In particular, adenoid hypertrophy can contribute to upper airway obstruction and is implicated in the pathogenesis of obstructive sleep apnea.

Peritonsillar Abscess

Peritonsillar abscess, also known as quinsy, refers to a localized collection of purulent material between the tonsillar capsule and the superior pharyngeal constrictor muscle. This complication arises when infection extends beyond the tonsillar capsule into the peritonsillar space. Clinical features include dysphagia, odynophagia, trismus, and a characteristic muffled or “hot potato” voice.[15] Examination may reveal enlarged, inflamed tonsils, bulging of the soft palate, and uvular deviation toward the contralateral side. Management options include needle aspiration, which is effective in up to 90% of cases. Antibiotic therapy should follow aspiration, with agents such as clindamycin that provide robust gram-positive coverage. Tonsillectomy is reserved for recurrent abscess formation and should be deferred until the acute infection has resolved.