This radiological view of the brain is not in exactly the same horizontal plane as the anatomical specimen shown in the previous illustration. The radiological images of the brain are often done at a slight angle in order to minimize the exposure of the stuctures of the orbit, the retina and the lens, to the potential damaging effects of the x-rays used to generate a CT scan.
A CT image shows the skull bones (in white) and the relationship of the brain to the skull. A piece of the falx cerebri can also be seen. The outer cortical tissue is visible, with gyri and sulci, but not in as much detail as an MRI (shown in the next illustration). The structures seen in the interior of the brain include the white matter, and the ventricular spaces, the lateral ventricles with the septum pellucidum, and the third ventricle. Note that the CSF is dark (black). The cerebellum can be recognized, with its folia, but there is no sharp delineation between it and the cerebral hemispheres.
Although the basal ganglia and thalamus can be seen, there is little tissue definition. Note that the head of the caudate nucleus "protrudes" (bulges) into the anterior horn of the (lateral) ventricle (as in the previous brain section). The lentiform nucleus is identified and the internal capsule can be seen as well, with both the anterior and posterior limbs, and the genu.
The CSF cistern is seen behind the tectal plate (the colliculi; also known as the tectum or the quadrigeminal plate, see Figure 9A and Figure 10) — called the quad-rigeminal plate cistern (seen also in the mid-sagittal views, Figure 17 and Figure 18, but not labeled); its "wings" are called the cisterna ambiens, a very important landmark for the neuroradiologist.
A regular CT can show an area of hemorrhage (blood has increased density), an area of decreased density (e.g., following an infarct), as well as changes in the size and shifting of the ventricles. This examination is invaluable in the assessment of a neurological patient in the acute stage of an illness or following a head injury and is most frequently used because the image can be captured in seconds. A CT can also be "enhanced" by injecting an iodinated compound into the blood circulation and noting whether it "escapes" into the brain tissue because of leakage in the BBB (discussed with Figure 21), for example, with tumors of the brain.
Gray matter White matter
Caudate n. (head)
Lentiform n. (putamen and globus pallidus)
Internal capsule: Anterior limb Genu
Posterior limb 3rd ventricle
F = Frontal lobe T = Temporal lobe
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