The brain consists of grey and white matter structures which are differentiated on CT by differences in density. White matter has a high content of myelinated axons. Grey matter contains relatively few axons and a higher number of cell bodies. As myelin is a fatty substance it is of relatively low density compared to the cellular grey matter. White matter, therefore, appears blacker than grey matter.
CT Brain Anatomy
Brain parenchyma and lobes
Key points
- Grey matter appears grey
- White matter appears blacker
Grey matter v white matter - CT brain
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Grey matter v white matter
- White matter is located centrally and appears blacker than grey matter due to its relatively low density
Clinical significance
- Pathological processes may increase or decrease the differentiation in density between grey and white matter
Brain lobes
The brain has paired, bilateral anatomical areas or 'lobes'. These do not exactly correlate with the overlying bones of the same names.
Brain lobes - CT brain (superior slice)
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Brain lobes - CT brain (superior slice)
- On both sides the frontal lobes are separated from the parietal lobes by the central sulcus (arrowheads)
- Note: The frontal lobes are large and the parietal and occipital lobes are relatively small
Brain lobes - CT brain (inferior slice)
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Brain lobes - CT brain (inferior slice)
- The most anterior parts of the frontal lobes occupy the anterior cranial fossae
- The temporal lobes occupy the middle cranial fossae
- The cerebellum and brain stem occupy the posterior fossa
Lobes v 'regions'
CT does not clearly show the anatomical borders of the lobes of the brain. For this reason radiologists often refer to 'regions', such as the 'parietal region' or 'temporal region', rather than lobes.
If more than one adjacent region needs to be described then conjoined terms can be used such as 'temporo-parietal region' or 'parieto-occipital region'
Lobes v 'regions'
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Lobes v 'regions'
- The parietal lobe is not clearly delineated from the temporal or occipital region