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Tonsillitis is an inflammation or infection of the tonsils, caused by either bacteria or viruses. The tonsils usually become swollen and very painful, making swallowing difficult. Sometimes the tonsils have spots of exudates (usually leukocytes) or pus on the surface. The surface of the tonsils is covered by recesses or crypts (cryptae tonsillares) that may branch and extend deep into the tonsil. The crypts often hold a variety of bacteria, some of which can cause tonsillitis.

The tonsils are conglomerations of lymphoid nodules, covered by a mucous membrane. They help to provide immune responses by, for example, providing lymphocytes and antibodies. There are three types of tonsils that form an irregular, circular band (Waldeyer's ring) around the throat, at the very back of the mouth. Tonsils are strategically located, guarding the opening to the digestive and respiratory tracts. The pharyngeal tonsils (adenoids) are embedded in the posterior wall of the pharynx. The lingual tonsils are located at the base of the tongue, and the palatine tonsils are the oval shaped masses situated on both sides of the throat.

The palatine, lingual, and pharyngeal tonsils. Illustration by Hans & Cassidy. Courtesy of Gale Group.

It is usually the prominent, palatine tonsils that become infected or inflamed, and these are the tonsils that are removed surgically (tonsillectomy) when medically indicated, to treat chronic tonsillitis or repeated episodes of acute tonsillitis. Occasionally the pharyngeal tonsils or adenoids are also removed surgically (adenotonsillectomy) if they cause ear infections, or block the Eustachian tubes or nasal passages. Adenoviruses (upper respiratory infection or "common cold") are the most common cause of viral tonsillitis. The Epstein-Barr virus (infectious mononucleosis) can also cause tonsillitis. The most common bacteria to cause tonsillitis are any of the group A streptococcus bacteria (Streptococcus pyogenes). Bacterial tonsillitis is treated with antibiotics. However, antibiotics are ineffective with viral tonsillitis. Symptoms can be relieved with aspirin (or other anti-inflammatories), gargling with saltwater, and rest.

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