Introduction

Tonsils are lymphoid tissue aggregates situated near the entrance of the digestive and respiratory tracts and play a key role in our immune system. They act as a front-line defense forming the initial immunological response to inhaled or ingested pathogens. The lymphatic tissues located in the oropharynx are composed of a circumferential tonsillar ring, known as the Waldeyer's ring which consists of the palatine tonsils (faucial tonsils), adenoid (nasopharyngeal tonsil), lingual tonsil, and tubal tonsils. When patients and doctors discuss tonsils, they are often referring to the palatine tonsils located at the back of the throat between the two palatine arches (pillars). 

Structure and Function

Like all lymphoid tissue, tonsils play a role in the immunity and body's defense against infections and foreign pathogens. The immunologic function of the tonsils is noteworthy.[1] When antigens are inhaled or ingested, tonsils are appropriately positioned for exposure which will lead to the development of lymphokines and immunoglobulins. Composed predominately of B-cell lymphoid tissue, one of the roles served by tonsils is that of mucosal secretory immunity. On the surface of the tonsils, one can find specialized antigen-capture cells referred to as M cells. These cells permit the capture of antigens generated by micro-organisms. The M cells, after recognizing an antigen, activate T and B cells in the tonsils and trigger an immune response.[2] B cells, when stimulated, proliferate in the germinal areas of the tonsils. At the germinal center, B memory cells mature and are stored for repeated exposure to the same antigen.[3] B cells also serve to secrete IgA, an antibody that plays a vital role in the immune function of mucus.[4] Newer studies indicate that tonsils also generate T lymphocytes, but the mechanism of production is different compared to the thymus.[5]

Tonsils share a common structure and function with other lymphatic tissues located within the gastrointestinal tract (Peyer's patches) which monitor intestinal bacteria populations and prevent the overgrowth of intestinal bacteria.

Embryology

Tonsils are derivatives of the 2nd pharyngeal pouch.[6] They typically appear around the 4th or 5th months of gestation and continue to develop with the growth of the child.[7] Present at birth, tonsils tend to reach the full size between the 6th and 8th years of life. Tonsils and adenoid tissue are found to be the most immunologically active between the 4th and 12th years of life and begin to involute/atrophy shortly after the first decade.[8]

Blood Supply and Lymphatics

• Tonsils lie along the lateral wall of the oropharynx, in a fossa located between the anterior and posterior pillars. Five arteries provide blood supply to the tonsils. They include the tonsillar branch of the facial artery (main supply), ascending palatine artery, dorsal lingual artery, ascending pharyngeal artery, and lesser palatine artery.[9] The venous drainage of the tonsils occurs primarily through the peritonsillar plexus of veins into the pharyngeal and lingual veins which drain into the internal jugular vein.[6]
• While not providing direct blood supply to the tonsils, it is important to note that the internal carotid artery is approximately 2.5cm posterolateral to the tonsils and requires precaution during surgeries to avoid accidentally cutting it.

Nerves

• Tonsils receive the afferent supply from the tonsillar plexus, with contributions from the trigeminal nerve (CN 5) via the lesser palatine nerves, as well as the glossopharyngeal nerve (CN IX).
• CN IX continues distally to the tonsils supplying general sensory and taste sensation to the posterior one-third of the tongue. CN IX is the nerve most likely to be damaged during a tonsillectomy.

Surgical Considerations

Tonsillectomy

• Surgical removal of tonsils is called a tonsillectomy.
• Hemorrhagic tonsillitis is an absolute indication for tonsillectomy.[10]
• Relative indications for tonsillectomy include[10]:
  • Recurrent or chronic pharyngotonsillitis
  • Peritonsillar abscess
  • Streptococcal carriage 
• Tonsils are surgically removed by dissecting between the tonsillar capsule and the superior constrictor muscle using either the “hot” or “cold” technique.  In the “hot” tonsillectomy technique, electrocautery is employed to dissect and coagulate simultaneously. In the “cold” tonsillectomy technique, a superior incision is made through the mucosal layers, and blunt dissection is used to separate the tonsils from the underlying tonsillar bed. Tonsils are then separated along their inferior border using the snare method. Studies have shown a superiority of the cold technique when looking at the outcome of postoperative pain. However, electrocautery minimizes intraoperative blood loss.[11] Newer techniques currently in practice employ the use of CO2 lasers, ultrasound, as well as radiofrequency ablation citing reduced postoperative pain though further research is necessary.
• Complications following a tonsillectomy classify into three main categories: acute, subacute, and delayed. Acute complications include airway obstruction due to edema, bleeding, and post-obstructive pulmonary edema. Subacute complications include postoperative hemorrhage, dehydration, and weight loss. Delayed or chronic complications include velopharyngeal insufficiency and nasopharyngeal stenosis.[11]
• Good practice advocates that the serious complications of tonsillectomy (profuse hemorrhage requiring blood transfusion and potentially fatal hemorrhage) be routinely discussed during the process of obtaining informed consent for tonsillectomy, despite their low occurrence rate. 'Reasonable patients' consider these complications to be significant and expect surgeons to discuss these complications with them. Surgeons, however, on the other hand, avoid discussing these serious complications with their patients.[12]
• The literature reports cases of fatality from massive hemorrhage as a result of tonsillectomy.[13][14]

Adenotonsillectomy

• In certain conditions, both tonsillectomy and adenoidectomy (surgical removal of the adenoid) are indicated.[15]
• Surgical excision of both the tonsils and adenoid is referred to as adenotonsillectomy.
• Absolute indications for adenotonsillectomy include[10]:
  • Adenotonsillar hyperplasia with obstructive sleep apnea
  • Abnormal dentofacial growth
  • Malignancy
• Dysphagia, speech impairment, and halitosis are relative indications for adenotonsillectomy.[10]
• Removal of the tonsils and adenoid does not produce any clinically significant immunologic deficiency.
• Various acquired or inherited bleeding disorders, anemia, acute infection and patients with high anesthetic risk are contraindications for adenotonsillectomy.[11]

Clinical Significance

Tonsilloliths

Tonsilloliths (tonsil stones) are whitish, malodorous concretions that develop in the tonsillar crypts arising from bacterial growth and retained cellular debris. They are most often asymptomatic but may lead to issues including halitosis, otalgia, and foreign body sensation. Management is conservative, and patients are encouraged to extract tonsilloliths by using cotton swabs. However, large troublesome tonsilloliths require surgical extraction. Mouth rinses and gargling may be beneficial in combating halitosis caused by tonsilloliths.[16]

Bacterial Tonsillitis

Acute bacterial tonsillitis may present with the sudden onset of throat pain, enlarged erythematous or exudative tonsils, malodorous breath, and tender cervical lymph nodes. It may be challenging to differentiate bacterial from viral etiologies of tonsillitis/pharyngitis. While the treatment of viral disease is mainly supportive care, the treatment of routine, mild tonsillitis is pain control and antibiotics (amoxicillin or macrolides). For recurrent tonsillitis, tonsillectomy is the recommended course. Current guidelines provided by the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) recommend surgical intervention for recurrent tonsillitis when a patient is found to have suffered seven infections in one year, five infections per year for two years, or three infections per year for three consecutive years.[17]

Adenotonsillar Disease

Adenotonsillar disease includes recurrent tonsillitis and adenoiditis. Patients can present with both acute and chronic infections of the adenoid. Infections of the adenoid are often mistaken for viral and bacterial upper respiratory infections as symptoms overlap and are difficult to differentiate. Adenoiditis is likely to present with fever, purulent nasal drainage, nasal obstruction and is commonly associated with otalgia. Group A beta-hemolytic streptococcus (GABHS, Streptococcus pyogenes) is a common cause of acute tonsillitis. Chronic inflammation of the tonsils and adenoid can result in hypertrophy. Adenoid hypertrophy may play a role in causing obstructive sleep apnea.[18]

Peritonsillar Abscess

Peritonsillar abscess is also called quinsy.[19] It is a collection of purulent fluid in the space surrounding the tonsils between the tonsillar capsule and the superior constrictor muscle. An abscess develops when infection penetrates the capsule and enters the peritonsillar space. Presenting signs and symptoms of a peritonsillar abscess include dysphagia, odynophagia, trismus, and a classic “hot potato” or muffled voice. Physical examination of the oral cavity will expose enlarged infected tonsils, a bulging soft palate (superiorly), and often reveals unilateral deviation of the uvula towards the side contralateral to the infection. Management may include needle aspiration in the clinic or emergency room, which has been shown to be effective in as high as 90% of cases. Antibiotics are recommended following needle aspiration and emphasis is placed on those with strong gram-positive coverage such as clindamycin. Tonsillectomy should be reserved for recurrent peritonsillar abscesses and should only take place following the resolution of infection.[20]