- effacement of basal cisterns
- loss of grey-white differentiation
- loss of sulci
- midline shift
- herniation of cerebellar tonsils into the foramen magnum
- uncal herniation
The features of uncal herniation are:
- shift of the brainstem and distortion of adjacent cisterns
- dilatation of contralateral temporal horn
- compression of the posterior cerebral artery as it crosses the tentorium, causing a posterior cerebral artery territory infarct
PATTERN OF BRAIN HERNIATION
- Uncal transtentorial herniation: the uncinate process of the temporal lobe herniates into the anterior part of the opening of the tentorium cerebelli.
- Central tentorial herniation: there is symmetrical downward movement of the thalamic region through the opening of the tentorium cerebelli
- Subfalcine herniation: there is displacement of the cingulate gyrus under the falx and across the midline
- Foraminal herniation: there is downward herniation of the cerebellar tonsils into the foramen magnum
The level of foramen magnum is measured on the saggital T1 image. It is defined as a line between the front (basion) and the back (opisthion) of the foramen magnum. The signal of cortical bone, not marrow must be used to define these landmarks.
There are two type of cerebral oedema:
1. Cytotoxic: intracellular oedema caused by cell swelling with an intact blood brain barrier. Cytotoxic oedema affects predominantly grey matter, with subsequent loss in grey-white matter differentiation. It generally accompanies stroke and hypoxia and gives a pattern of "restricted diffusion" on MRI sequences
2. Vasogenic: extracellular oedema caused by loss of integrity of the BBB. Vasogenic odema predominantly affects white matter and spreads along white matter tracts, accentuating the grey-white matter differentiation. It generally accompanies inflammatory disease and brain tumors. It does not give a pattern of "restricted diffusion" on MRI sequences.
http://en.wikipedia.org/wiki/Brain_herniation
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