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Chapter 11
Nervous system diseases
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Diseases of the nervous system present with a rather bewildering combination of clinical symptoms and signs. For a clinician to make sense of these, it is necessary to have some knowledge of the anatomy and of the pathologies that may occur.
Clinical examination should help to identify the anatomical site of the problem, and a knowledge of the possible pathologies that may occur should be a guide to the further investigations, immediate treatment and further management.
The major pathologies encountered are
Pathology of the arteries or veins which result in cerebrovascular accidents (CVA’s or strokes)
Abnormalities in the circulation of the cerebro spinal fluid (CSF)
Congenital anomalies
Neural tube defects
General diseases
Dementia:for example, Alzheimer’s disease in adults and tuberous sclerosis in children
Parkinson’s disease
Multiple sclerosis
Infections
Tumours
Benign, malignant and metastatic
The pathological entities to be illustrated in this chapter provide a basis for the practical knowledge needed to interpret the clinical findings in patients presenting with diseases of the nervous system.
Normal anatomy
Before embarking on a discussion of the pathology of the nervous system it is necessary to know something about the normal anatomy so as to be able to understand and interpret the symptoms and signs of diseases of the nervous system with which patients present.
Anatomical parts of the brain
1(a) and (b)
(a) These diagrams indicate the main gross features of the brain as seen from above and from the under surface of the brain.
The brain surface is folded (concertinered) so that a large surface area can be packed into a smaller space. These folds are called gyri.
The wavy black lines in the diagrams are spaces between the gyri and they are called sulci.
Black arrows frontal lobe.
Blue arrows occipital lobe.
Green arrow temporal lobe.
Grey arrow parietal lobe.
Red arrow cerebellum.
Brown arrow pons.
Yellow arrow medulla (or medulla oblongata) The anterior part of the medulla contains the pyramids which carry the motor fibres from the cortex to the spinal cord.
Orange arrow spinal cord.
Light blue arrow in the right hand diagram is the central sulcus. The gyrus anterior to this sulcus is the central gyrus and it contains the motor neurons in its grey matter. It is sometimes called the motor cortex.
Purple arrow indicates the two optic nerves and the optic chiasm in which half the sensory fibres from each eye cross to the other side of the brain.
(b) This is a normal brain for comparison with the diagram.
The black arrow indicates where some of the leptomeninges have been stripped from the surface of the brain. The cortex to the right of the arrow has no leptomeninges, while to the left the leptomeninges are intact.
2(a) and (b)
(a) The right lateral view of the brain with the same coloured arrows as before. The light blue arrow indicates the lateral sulcus that marks the superior extent of the temporal lobe.
When this sulcus is opened, the insula which runs vertically in its base can be seen
The other coloured arrows are as in the previous figures.
(b) This is a view of the right lateral surface of the brain of an adult who had dementia caused by Alzheimer’s disease.
The leptomeninges have been stripped off so that the cortical surface can be seen more clearly.
The brain is atrophied and smaller than normal. The gyri are thinner than normal which makes the distinction between gyri and sulci more obvious.
Can you identify the various parts of the brain from the diagram in 03?
3(a) and (b)
(a)
5 The left medial view of the brain. The arrows are the same colours as before except for the following:
The light blue arrow indicates the pituitary gland.
The yellow arrow is the corpus callosum.
The grey arrow is the fornix.
The orange arrow is the choroid plexus.
(b)Left medial view of the brain shown in Fig 04.
Can you identify the various anatomical features illustrated in the diagram, and can you identify some other anatomical features not mentioned in the diagram?
4(a) and (b)
(a)The cranial nerves are paired.
Red arrow. Cranial nerve I (olfactory nerve) sense of smell. Its distal end is widened and this is called the olfactory bulb.
Purple arrow cranial nerve II. (optic nerve) sense of sight.
Yellow arrow cranial nerve III (oculomotor nerve) Eye movements
Orange arrow cranial nerve IV. It is thin and is the motor nerve to the superior oblique muscle which moves the eye downwards and outwards.
Black arrow cranial nerve V. A big nerve that arises from the middle of the pons and is sensory to the face.
Nerves VI, VII and VIII arise from the lower border of the pons.
Green arrow cranial nerve VI which is motor to the lateral rectus muscle of the eye.
Light blue arrow the medial half of this nerve bundle is cranial nerve VII (facial nerve) motor to the face muscles.
Light blue arrow the lateral half of the nerve bundle is cranial nerve VIII (auditory nerve) sense of hearing.
Cranial nerves IX to XII arise from the anterolateral surface of the brain stem.
Brown arrow cranial nerves IX, X and XI.
Grey arrow cranial nerve XII. (vagus nerve)
(b)In this image the under surface of the brain is shown and the cranial nerves are arrowed.
The specimen is not perfect because the brain was not removed as carefully as it should have been. Hence not all the paired nerves can be seen.
The nerves are labelled with the same coloured arrows as in the diagram.
The orange arrow indicates where the IVth nerve should be.
The white arrow indicates the base of the brain from which the pituitary gland arises. It has been left in the base of the skull in the pituitary fossa when the brain was removed.
5This is a view of the base of the skull from which the brain has been removed.The stalk of the pituitary gland is marked by a green arrow.
The pituitary is in a bony compartment called the pituitary fossa. The blue arrows indicate the internal carotid arteries.
The outer sides of the lateral walls of the pituitary fossa are lined by layers of dura mater in which pass the cavernous sinus, the carotid artery and the cranial nerves, 111, 1V, V and VI.
Pathology in the region of the pituitary fossa causes pressure on one or more of these cranial nerves and paralysis of one of these nerves is a good sign of the site of such pathology.
Autonomic system
There are two components sympathetic and parasympathetic.
They have complex connections throughout the brain and spinal cord.
One component of the system that can be seen naked eye and which has some clinical associations is the sympathetic trunk.
This is a recognizable length of nerve fibers that has ganglia (nodules of aggregated neurons) placed at regular intervals along the ‘trunk.’
The sympathetic trunk runs along the anterolateral aspect of the vertebral bodies for the whole length of the spinal column from the base of the skull to the coccyx.
6 Diagram of the sympathetic trunk.
Clinical aspects of the sympathetic trunk
The operation of lumbar sympathectomy is done to improve the blood supply to arteries in an ischaemic leg.
The operation consists in excision of a segment of the sympathethic trunk (sometimes called the sympathetic chain).
Cervical sympathectomy may be done for similar reasons, and sometimes to relieve intractable pain.
Destruction of the upper portion of the thoracic section of the sympathetic trunk results in a clinical syndrome called Horner’s syndrome.
By far the commonest cause of this is infiltration by a lung cancer in the apical segment of the right lung.
Examples of clinical signs that can be correlated with the anatomy.
Cranial nerve palsies
7 This man has been asked to look to his right. His right eye has not moved, which indicates that he has a right lateral rectus muscle paralysis.
This was due to a pituitary tumour expanding his pituitary fossa and damaging his right VIth nerve.
8(a), (b), (c)
(a) This woman has been asked to look to her right while keeping her head still.
Her right eye has not moved, indicating that she has paralysis of the right VIth nerve.
(b) She has been asked to put out her tongue.
It deviates slightly to the right, and the right side is slightly atrophic as compared with the left side.
She has a paralysis of her right XIIth nerve.
The only place where both of these nerves can be damaged at the same time is where they leave the brain stem between the lower border of the pons where the right VIth nerve emerges, and the lower part of the medulla where the right XIIth nerve emerges from the brain stem.
In fact she had a tumour that arose from the tissue covering the brain at this site. It was removed surgically.
(c)
The blue line represents the VIth nerve arising from the lower border of the pons and running forwards through the cavernous sinus beside the pituitary gland and through the posterior aspect of the orbit and then innervates the lateral rectus muscle of the eye.
The green line represents the XIIth nerve emerging from the brain stem between the pyramid and the olive, leaving the skull via the foramen in the mastoid bone and passing forward in the floor of the mouth to innervate the tongue.
The red square represents the site of the tumour that was surgically removed from this patient.
9This boy has involvement of the middle (maxillary) branch the right Vth nerve by herpes zoster. The herpes zoster infection involves a cranial nerve or a spinal nerve trunk unilaterally. This case demonstrates the way in which the Vth nerve supplies sensation to the face.The Vth nerve has 3 branches - ophthalmic, maxillary and mandibular.
10(a) and (b)
(a) This man has paralysis of the right V11th nerve.
The right side of his forehead is not wrinkled.
His right eye will not close
and the right side of his face is drooping.
He was dribbling saliva from the right side of his mouth.
This paralysis has been accentuated by asking him to ‘show his teeth.’
The main causes of VIIth nerve palsy are CVA (stroke), Bell’s palsy and traumatic damage to the nerve.
Bell’s palsy is a sudden onset of unilateral paralysis of the VIIth nerve.
Its cause is not known except that it may follow a viral infection.
It may be transient or permanent.
(b) Operative dissection of the left VIIth nerve.
The branches of the nerve (black arrows) have been displayed after the superficial lobe of the parotid gland has been removed as treatment of a pleomorphic adenoma of the parotid.
It is important to carefully preserve all the branches of the nerve or else the patient will have post operative partial paralysis of the VIIth nerve.
11This patient has herpes zoster of the right first lumbar nerve root
The erythematous, vesicular rash involves one nerve root unilaterally.
It extends for a variable distance from the midline (the vertebral column) in the back to the midline anteriorly.
The rash demonstrates the distribution of a nerve root which sweeps downwards and around to the anterior abdominal wall.
12 Diagram of the surface markings of the nerve roots
Horner’s syndrome
13(a) and (b)
(a)
(a) This 67 year old man has a Horner’s syndrome.
He has ptosis of the right eyelid.
The right eye is smaller than the left one and it is sunken into the orbit (enophthalmos)
The pupil of the eye is small and it does not respond to light stimulus.
There is no sweating on the right side of his face although there is profuse sweating on the left side.
Note that he has the blue marks of the radiotherapist over the left side of his upper chest.
(b)
(b) Chest X-ray shows that he has an advanced lung cancer involving the apical segment of his right lung.
The tumour has invaded the upper portion of the right thoracic sympathetic trunk.
Blood supply to the brain
I will begin with the arterial supply and illustrate some of the pathology associated with arteries. Then I will illustrate the normal venous supply and the pathologies that affect the veins.
Arterial supply
The brain has a double arterial supply.
Vertebral arteries:
One vertebral artery arises from each subclavian artery in the base of the neck. They pass through foramena in the lateral processes of the cervical vertebrae and enter the skull through the foramen magnum on the anterior surface of the upper cervical cord and medulla. At the inferior border of the pons they fuse to form the basilar artery.
Internal carotid arteries:
A right and a left common carotid artery arise from the arch of the aorta. In the upper neck they divide into an internal and an external branch.
The external supplies blood to the face and neck, while the internal one enters the skull through a foramen in the base of the skull. It passes in the cavernous sinus and then forms the main blood supply to circle of Willis.
The circle of Willis consists of the internal carotid arteries, the middle cerebral arteries, the anterior cerebral arteries and the posterior communicating branch which connects with the posterior cerebral artery.
14This diagram illustrates the main arterial supply to the brain.
Yellow arrow vertebral artery
Red arrow basilar artery
Brown arrow posterior cerebral artery
Grey arrow internal carotid artery with the middle cerebral artery shown as a light blue hatched line.
Light blue arrow anterior cerebral artery. The two anterior cerebral arteries are connected by a small anterior communicating artery.
The internal carotid arteries are connected to the posterior cerebral arteries by posterior communicating branches.
Black arrow superior cerebellar artery arising from the distal end of the basilar artery.
Blue arrow anterior inferior cerebellar artery arising from the proximal end of the basilar artery.
Green arrow posterior inferior cerebellar artery arising from the vertebral artery.
(a)
(b)
15(a) and (b)These diagrams give some idea of the brain territories supplied by the three main cerebral arteries.
Blue area middle cerebral artery
Brown area posterior cerebral artery
Green area anterior cerebral artery
16 This is a real dissection of the arteries that form the circle of Willis at the base of the brain.
Brown arrows anterior cerebral arteries
Light blue arrow anterior communicating artery
Yellow arrow internal carotid arteries
Blue arrows middle cerebral arteries
Green arrows posterior communicating arteries
White arrows posterior cerebral arteries
Purple arrow superior cerebellar artery
Red arrow basilar artery
Grey arrow vertebral artery
I think that the easiest way to understand the arterial and venous systems of the brain is to see some of the effects of pathology in arteries and veins. The pathology in veins will be dealt with after the anatomy of the veins is demonstrated.
Pathology in arteries
The underlying pathology in arteries is atherosclerosis and hypertension.
Complications of these pathologies
Infarction caused by occlusion of arteries by either thrombi or emboli.
Haemorrhage from rupture of their walls as a result of hypertension.
The artery most often involved is the middle cerebral artery.
Infarction
(a)
(b)
17(a) and (b)
(a) This middle aged patient died from a ‘stroke.’
The post mortem examination of the brain indicated that there had been an infarction of the brain tissue in the distribution of the right middle cerebral artery.
The brain tissue involved felt abnormally soft.
In (a) both middle cerebral arteries are exposed.
In (b) it can be seen that the right middle cerebral artery (black arrow) is filled with thrombus because it is a solid blue colour which is different from the colour of the left artery.
The posterior communicating artery also appears to be thrombosed (blue arrow) and there is haemorrhagic infarction of the cerebral peduncles.
This would indicate that the thrombotic occlusion was at the bifurcation of the right internal carotid artery.
Can you also see a small unruptured aneurysm on the anterior communicating artery?
Small branches from the middle cerebral artery supply blood
to the internal capsule on the deep aspect of the artery