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

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 ?
Mannitol 0.5 g/kg can be given if there is evidence of coning (downward tonsillar herniation).
Death in this individual can be explained by tonsillar herniation, and distortion and compression of the medulla by the tumor.
There was right cingulate herniation, but no uncal or tonsillar herniation. On coronal sections, the right cerebral hemisphere showed a large mass lesion, which measured 5 x 4 cm in cross-section, involving the basal ganglia and internal capsule (Figure, A).
et al., "Tonsillar herniation on MRI," Neurosurgery 1988, 22, pp 77-80.
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.