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1. either of two small masses of lymphatic tissue situated one on each side of the back of the mouth
2. Anatomy any small rounded mass of tissue, esp lymphatic tissue
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


Localized aggregation of diffuse and nodular lymphoid tissue found in the region where the nasal and oral cavities open into the pharynx. The tonsils are important sources of blood lymphocytes. They often become inflamed and enlarged, necessitating surgical removal.

The two palatine (faucial) tonsils are almond-shaped bodies measuring 1 by 0.5 in. (2.5 by 1.2 cm) and are embedded between folds of tissue connecting the pharynx and posterior part of the tongue with the soft palate. These are the structures commonly known as the tonsils. The lingual tonsil occupies the posterior part of the tongue surface. It is really a collection of 35–100 separate tonsillar units, each having a single crypt surrounded by lymphoid tissue. Each tonsil forms a smooth swelling about 0.08– 0.16 in. (2–4 mm) in diameter. The pharyngeal tonsil (called adenoids when enlarged) occupies the roof of the nasal part of the pharynx. This tonsil may enlarge to block the nasal passage, forcing mouth breathing. See Lymphatic system

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


Localized aggregation of diffuse and nodular lymphoid tissue found in the throat where the nasal and oral cavities open into the pharynx.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Sagittal cervical MRI imaging are usually four (4) to five (5) millimeter slices which can miss detailed structures of the CCJ like cerebellar tonsils, which are small peg-like structures at the base of the brain, and CCJ ligaments, which average two (2) mm in diameter.
The obex position is low and the cerebellar tonsils are also herniated beyond normal range.
There was no herniation of the temporal lobe unci or cerebellar tonsils. On coronal sections, the left frontal lobe exhibited a 3-cm cavitary lesion filled with necrotic and gelatinous material.
In clinical practice, SIH may manifest itself as a loss of the prepontine cistern due to leak of CSF, with flattening of the brainstem and downward herniation of the cerebellar tonsils, which may mistakenly lead to a diagnosis of Chiari I malformation (10,11).
In pediatric clients, the Chiari I malformation may spontaneously correct as the cerebellar tonsils rise normally with growth.
Chiari I malformation consists of herniation of the cerebellar tonsils into the foramen magnum, thus crowding the craniocervical junction.
(1) cerebellar tonsils are situated above the foramen magnum, although occasionally it may pass through the foramen magnum.
Computed Tomography Scan of the head showed multiple hypodense areas in the cerebellum, inferior herniation of cerebellar tonsils with obstructive hydrocephalus.
Subsequent magnetic resonance imaging detected a herniation of the cerebellar tonsils to the level of C2 and the presence of a cervical syrinx--findings consistent with a Chiari I malformation.
Disturbances to the cerebellum result in decrease muscle tone on the ipsilateral side, poor coordination of fine motor movements and problems with gait.[23] Other problems include ataxia, intention tremor, diadochokinesia, dysmetria, hypotonia and asthenia.[11] Another important problem which may occur, especially in a hemorrhagic stroke or other situations leading to increased intracranial pressure, is the downward movement of the cerebellar tonsils through the foremen magnum resulting in a tonsillar herniation and compression of the medulla.[18]
Chiari I Malformation: Chiari I malformation is characterized by inferior displacement of cerebellar tonsils into the rostral cervical spinal canal (Figure 4).
Basal skull and cervical spine CT findings include spinal canal stenosis, mild platybasia with angulation and compression into the cervicomedullary junction, and downward displacement of the cerebellar tonsils (Figure 4).