tonsillar herniation

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abnormal protrusion of an organ or other body structure through a defect or natural opening in a covering membrane, muscle, or bone. (See also hernia.)
Herniation syndromes. From Ignatavicius and Workman, 2002.
caudal transtentorial herniation transtentorial herniation.
central herniation a downward shift of the brainstem and the diencephalon due to a supratentorial lesion, causing Cheyne-Stokes respirations with pinpoint nonreactive pupils.
cingulate herniation a shift of the cingulate gyrus to below the falx cerebri.
disk herniation (herniation of intervertebral disk) (herniation of nucleus pulposus) herniated disk.
tentorial herniation transtentorial herniation.
tonsillar herniation protrusion of the cerebellar tonsils through the foramen magnum.
transtentorial herniation downward displacement of medial brain structures through the tentorial notch by a supratentorial mass, exerting pressure on the underlying structures, including the brainstem; this is a life-threatening situation because of pressure on the third cranial nerve, with symptoms including dilated, nonreactive pupils, ptosis, and a decreased level of consciousness. Called also caudal transtentorial herniation, tentorial herniation, and uncal herniation.
uncal herniation transtentorial herniation.

ton·sil·lar her·ni·a·tion

herniation of the cerebellar tonsils through the foramen magnum.

tonsillar herniation

Etymology: L, tonsilla + hernia, rupture
the herniation of tonsils of the cerebellum through the foramen magnum of the skull. It may occur as a result of intracranial pressure from an injury or tumor.

tonsillar herniation

The protrusion of the cerebellar tonsils through the foramen magnum. It causes pressure on the medulla oblongata and may be fatal.
See also: herniation
References in periodicals archive ?
Factor analysis and validity tests were performed on the initial 70-item questionnaire using a convenience sample of eight adult patients (all over 17 years old) diagnosed with CMI by MRI criteria of tonsillar herniation of 5 mm or greater.
Death in this individual can be explained by tonsillar herniation, and distortion and compression of the medulla by the tumor.
CT scan and Magnetic Resonance Imaging (MRI) of the brain revealed multiple hematomas in left frontal and high parietal lobe, in right cerebellar hemisphere, downward tonsillar herniation and indentation of the posterior eyeball suggestive of raised intracranial tension.