1-If we look to the brain we observe that is formed of two cerebral hemispheres, brain stem and also two cerebellar hemispheres.
2-In transverse sections of the brain we can classify the sections into three groups.
3-The first group is from the base of the skull till you can see the lateral ventricles.
4-The second group is the sections running through lateral ventricles.
5-The third group of sections are the sections running from the second group till reaching the vertex of the skull.
6-The land mark of the first group is the fourth ventricle where you can find in front of it the brain stem and posterior to it the cerebellar vermis while postero-lateral to it is the cerebellar hemispheres.
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7-The brain stem is formed from three parts which are from above to down the mid brain, pons then the medulla.
8-The largest part of the fourth ventricle when meeting the largest part of the brain stem which is the pons.
9-So when the fourth ventricle is in its biggest size, I will know that the part in front of it from the brain stem is the pons.
10-Junction between the cerebellum and pons is known as middle cerebellar peduncle.
11-The cerebellum is connected to the brain stem by three peduncles
-Superior peduncle connects mid brain with cerebellum.
-Middle peduncle connects pons with cerebellum.
-While inferior peduncle connects medulla oblongata with cerebellum.
-The middle cerebellar peduncle is the only one can be seen which also known as cerebello-pontine junction.
-The area in front of the pons is formed of cerebro-spinal fluid which is known as pre pontine cistern which contains basilar artery supplying the brain stem.
12-If we go down or up from the level of pons we observe that the fourth ventricle becomes smaller in size.
13-When we are down so the part of the brain stem in front of it is medulla.
14-When we are up so the part of the brain stem in front of it is mid brain, here you can notice that there is a very important structure which is quadrigeminal cistern which appears as a plate surrounding the mid brain.
15-The land mark of the second group is the lateral ventricles.
16-Each one is formed from anterior to posterior by frontal horn, body, occipital horn then temporal horn.
17-Each one of these lateral ventricle opens in the third ventricle by foreman of Monroe.
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| Red area is caudate nucleus while dark yellow area is the lentiform nucleus, light green area is the thalamus while the light blue area between the thalamus and lentiform nucleus is the posterior limb of the internal capsule, light yellow area between the caudate nucleus and lentiform nucleus is the anterior limb of internal capsule then the light area area outside the lentiform nucleus is the external capsule |
18-The first level of the second group is known as the level of basal ganglia which are formed from the caudate nucleus, lentiform nucleus and the thalamus.
19-The caudate nucleus(red area) is lying inside the concavity of the frontal horn then to the outside of it is lentiform nucleus(dark yellow) and on each sides of the third ventricle is the thalamus(light green).
20-The internal capsule is formed from anterior limb, posterior limb and genu.
21-The anterior limb(light yellow) is passing in between the caudate nucleus and lentiform nucleus.
22-While the posterior limb(light blue) is passing in between the thalamus and lentiform nucleus.
23-Finally the genu is the part connecting anterior and posterior limbs of the internal capsule.
24-External capsule(light yellow) is running outside the lentiform nucleus.
25- Normal anatomy of the vellum interpositum
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| Noncontrast CT scan of the head. Red arrow: Calcifications in the pineal gland. Yellow arrow: Internal cerebral veins. |
The cavum velum interpositum
Comment: The velum interpositum (Latin: the interposed roof) refers to the structures forming the roof of the third ventricle, in particular, the tela choroidea. The tela choroidea is a double layer of pia mater that covers the thalamus below and the floor of the body of the lateral ventricle above. The space between is subarachoid space which extends laterally ending at the choroidal fissure.
26- The second section in the second level is cutting in the body of ventricles which surounded by right and left hemispheres which are formed from white and grey matter.
28-How we can know that the lesion is in what lobe of the brain.
A-At the level of the caudate nucleus we make an anterior line transversely passing through the frontal horns of the lateral ventricles and another posterior line passing through the occipital horns.
-The part of the brain anterior to the anterior line is the frontal lobes.
-The part of the brain posterior to the second line is occipital lobes.
-The part between the anterior and posterior lines, look if you can see the third ventricle, so you are down and what is beside are the temporal lobes, if you can not see the third ventricle, so you are up where you can see the parietal lobes on both sides.
B-If you are at the level of the body of the lateral ventricle, draw an anterior line in the anterior end of the body and another line in the posterior end of the body of the lateral ventricle, anterior part of the brain anterior to this anterior line is frontal lobes while posterior line posterior to it is occipital lobes and in between two lines is parietal lobes.
C-If you go more up after disappearance of the lateral ventricles,you can divide the slice to four quarters, the anterior quarter is the frontal lobes, the second quarter posterior to the anterior one is the parietal lobes, the third quarter is also parietal lobes and then the posterior quarter is the parietal lobes also. So the anterior quarter is belong to the anterior lobes while the other three quarters are belong to parietal lobes.
D-Till you reaches the vertex where the only brain seen is the parietal lobes.
Comment: The velum interpositum (Latin: the interposed roof) refers to the structures forming the roof of the third ventricle, in particular, the tela choroidea. The tela choroidea is a double layer of pia mater that covers the thalamus below and the floor of the body of the lateral ventricle above. The space between is subarachoid space which extends laterally ending at the choroidal fissure.
26- The second section in the second level is cutting in the body of ventricles which surounded by right and left hemispheres which are formed from white and grey matter.
28-How we can know that the lesion is in what lobe of the brain.
A-At the level of the caudate nucleus we make an anterior line transversely passing through the frontal horns of the lateral ventricles and another posterior line passing through the occipital horns.
-The part of the brain anterior to the anterior line is the frontal lobes.
-The part of the brain posterior to the second line is occipital lobes.
-The part between the anterior and posterior lines, look if you can see the third ventricle, so you are down and what is beside are the temporal lobes, if you can not see the third ventricle, so you are up where you can see the parietal lobes on both sides.
B-If you are at the level of the body of the lateral ventricle, draw an anterior line in the anterior end of the body and another line in the posterior end of the body of the lateral ventricle, anterior part of the brain anterior to this anterior line is frontal lobes while posterior line posterior to it is occipital lobes and in between two lines is parietal lobes.
C-If you go more up after disappearance of the lateral ventricles,you can divide the slice to four quarters, the anterior quarter is the frontal lobes, the second quarter posterior to the anterior one is the parietal lobes, the third quarter is also parietal lobes and then the posterior quarter is the parietal lobes also. So the anterior quarter is belong to the anterior lobes while the other three quarters are belong to parietal lobes.
D-Till you reaches the vertex where the only brain seen is the parietal lobes.
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