- < 6 hours:
hyperacute haemorrhage, significant hypodense component due to unclotted blood.
- 6 hours to 3 days:
homogeneously hyperdense, if there is ongoing active bleeding may see the swirl sign
- 3 days to 3 weeks:
isodense to cerebral parenchyma
- chronic haemorrhage:
hypodense to brain and may looks like CSF
- bilateral hypodense areas in the lentiform nuclei (“owls eyes” in the basal ganglia)
Elevated Intracranial Pressure
- effacement of the basal cisterns
- loss of grey-white differentiation
- loss of sulci
- midline shift
- herniation of cerebellar tonsils into foramen magnum
- uncal herniation (shift of brainstem and distortion of adjacent cisterns, dilation of contralateral temporal horn, compression of the posterior cerebral artery as it crosses the tentorium -> posterior cerebral artery territory infarct)
- small, deep subcortical infarcts less than 1.5cm in size
- usually involve: basal ganglia, thalamus, internal capsule, corona radiate and brainstem
- two types:
(1) cortical border zone infarctions between the territories supplied by anterior, middle and posterior cerebral arteries
(2) internal border zone infarctions between the territory of the penetrating arteries arising form the superficial pial plexus and territories of the deep penetrating arteries arising from the basal cerebral arteries (corona radiate and centrum semiovale adjacent to the lateral ventricles)
- 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 herination: displacement of the cingulated gyrus under the falx and across the midline.
- foraminal herniation: there is downward herniation of the cerebellar tonsils into the foramen magnum.
Rim contrast enhancing lesions
- infections (toxoplasmosis)