"NERVOUS SYSTEM (SURGERY). - The purpose of this article is to give a general view of the scope and limitations of surgery as applied to injury and disease of the nervous system. It is essentially concerned therefore with the principles of modern surgical neurology rather than with clinical, pathological or technical details.
The nervous system (see 19.400) is unique among the various systems into which the body is conventionally divided by the descriptive anatomist in being everywhere sharply marked off by definite anatomical and physiological boundaries from all the other tissues. It is a system in the strictest sense of the term. Its substance is elaborately insulated from contact with nonneural tissues except at the minutely limited points where contact is necessary for function, and correspondingly its pathology comprises principles which are characteristic and peculiar to it. In the mechanisms of injury or disease, in the processes of recovery and repair and in the response to the action of drugs the nervous system displays qualities which are special to it and not to be found elsewhere. It is natural therefore that the general principles of surgery need to be qualified in certain ways before they can be applied satisfactorily to surgical neurology.
The three great divisions of the nervous system - brain, spinal cord and peripheral nerves - coincide nearly enough with differences of surgical principle to allow the surgery of them to be dealt with under corresponding heads.
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The brain differs from all other organs of the body in being enclosed in a capsule of bone, and in a capsule therefore which is incapable of being stretched by any physiological force. The normal response of other organs to injury or disease is swelling, and this possibility of the occurrence of swelling allows of the presence of inflammatory products, of extravasated blood or oedema fluid without the circulation of blood through the organ being grossly impeded. In the case of the brain swelling the result of injury or disease is strictly limited by the skull, with the result that products of inflammation (or extravasated blood) or oedema fluid press on the vessels of the brain - veins, venules and capillaries according to the amount of exudation - and limit the circulation through them. The consequence is that any intracranial lesion other than a purely degenerative one is always accompanied by more or less wide-spread circulatory disturbances in the brain.
Now the functional activity of the brain is immediately dependent on blood supply, so that a cerebral lesion, as it necessarily interferes with blood supply, must always produce disturbances of function by this mechanism. In the case therefore of a given lesion such as a tumour or a haemorrhage the symptoms will be produced in two ways. First there will be symptoms due to loss of the function of the piece of brain occupied and destroyed by the tumor or haemorrhage, and secondly there will be symptoms due to disturbance of function in the surrounding region of brain where the circulation is impeded by pressure.
This dual causation of symptoms is a fundamental principle in cerebral pathology, and there are two corollaries of it of equal importance. In the first place the loss of function due to circulatory disturbance may be and frequently is as complete as if it were due to actual destruction of the brain substance; and in the second place the symptoms due to circulatory disturbance are in the majority of cases more conspicuous and more important than those due to the directly destructive effect of the lesion. It follows from these considerations that in many cases in which surgery is unable to deal curatively with the actual diseases itself it can produce benefit by dealing with secondary circulatory disturbance through the relief of pressure. Since the secondary pressure effects of many cerebral tumours are extremely distressing (severe headache, persistent vomiting and failure of vision), the merely palliative relief of abnormal intracranial tension is an important function of cerebral surgery.
While disturbance of function due to circulatory embarrassment can be got rid of if the abnormal intracranial tension can be completely relieved, loss of function due to destruction of the brain substance is permanent. There is no such thing as regeneration of the brain tissue, or the taking over of the actual function of a destroyed part by another part, and surgery can do nothing to restore a piece of brain that has been destroyed.
Having defined the general limitations within which the surgeon works in dealing with injury or disease of the brain we may next indicate in a summary way the chief procedures he is called upon to undertake.
By this term is meant procedures which are intended to do away with the primary cause of the symptoms in a given case, but it is of course to be understood that any element in the symptoms that may be due to destruction of brain tissue is necessarily irremediable.
When the brain has been severely bruised either locally or diffusely - a common result of head injury in civil and military practice - the subsidence of the contusion is very slow, and may be indefinitely delayed owing to the effects of the rigid encapsulation by the skull. In these circumstances the patient is apt to suffer for many months or even years from severe and disabling symptoms of which the most conspicuous is headache. Such symptoms can be arrested by the making of an opening in the skull and dura mater, which allows the brain to expand and the contusion to subside. Apart from injury certain cases occur in which increased intracranial tension develops in a way that suggests the existence of a cerebral tumour. An operation, however, discloses no tumour but a great increase of pressure, which subsides after an opening is made in the skull.
In these two types of cases the mere relief of tension is curative and when the opening in the skull has done its work it can be closed by a plastic operation.
When as the result of injury a large collection of blood forms on the surface of the brain, death necessarily follows unless the blood clot is removed by operation. If the blood remains fairly localised and the diagnosis is made early, treatment by operation is often brilliantly successful. Haemorrhage into the brain not due to injury - apoplexy - can occasionally be evacuated by operation with success. Unless, however, the patient is relatively young and otherwise healthy the prospect of success in a given case is very small. Most of the symptoms of haemorrhage of all kinds are due to secondary circulatory disturbance, but in so far as they are due to destructive disorganization they are beyond remedy, so that while a successful operation for apoplexy may save a patient's life it may leave him permanently paralyzed.
(c) Operations for Abscess of the Brain. - Abscess in the brain is due to the entry of pus-forming micro-organisms as the result of injury such as bullet wound, to extension from an infective focus near the skull such as inflammations of the ear and nose, or to micro-organisms reaching the brain through the blood stream from an infective focus elsewhere in the body, especially in the chest. In the two types first named the evacuation of the abscess according to the general principles of surgery is frequently successful; in the third type evacuation usually fails, because there are multiple abscesses or because the patient is too enfeebled.
(d) Operations for Tumour of the Brain. - Intracranial tumours are of three principal types of structure according to the situations in which they arise - tumours of the brain substance are gliomas, tumours of the membranes of the brain are endotheliomas, and tumours of the cranial nerves are neuro-fibromas. The glioma grows in the brain substance which it usually infiltrates; sometimes it is partially differentiated from the surrounding brain by an imperfectly formed capsule. If it is to be removed with any prospect of freedom from recurrence it must be taken out with a margin of apparently healthy tissue about it. Thus in extirpating a glioma a considerable amount of gross and irrecoverable damage is as a rule necessarily inflicted on the brain. It is in fact rarely the case that the prospect even then of securing permanent freedom from recurrence is good enough to justify the disability that the operation of itself is likely to cause. Endothelioma of the membranes does not infiltrate the brain substance, and can therefore be removed without the necessary infliction of any serious damage to the brain. When in an accessible situation and recognized fairly early it is the tumour which offers the best chance of cure with the least risk. Neuro-fibroma is almost confined to one situation, the auditory nerve in its course between the brain and the temporal bone of the skull. It thus lies in close relation to the cerebellum, is usually associated with cerebellar symptoms, and being separated from the surface of the skull by the lateral lobe of the cerebellum is in an extremely inaccessible situation. The tumour in itself is benign and slow growing, and owes its seriousness solely to the great technical difficulties of the operation to remove it. In favourable circumstances, however, the operation may be satisfactory. These three representative neoplasms if untreated necessarily cause death; the only curative treatment of them is operative removal; the surgery of them while always difficult and frequently discouraging yields a sufficient number of wholly successful results to make application of it imperative in every case. At the present time the greatest obstacle to success is the difficulty of early and precise diagnosis. The dangers and difficulties of operations are greatly increased by the onset - sooner or later inevitable - of a severe and widespread increase of intracranial tension. Unfortu nately it is often only on the evidence of this complication that a diagnosis is now made. Two lines of investigation are being pursued to-day which offer some hope of greatly improved diagnosis in cases of cerebral tumour. These are the radiographic examination of the ventricles of the brain after air has been injected into these cavities, and the artificial and temporary intensification of states of cerebral disturbance so that latent symptoms become manifest.
In a large proportion of cases of cerebral tumour the surgeon is unable to carry out a radical operation. This may be because the tumour cannot be found, because its situation is inaccessible, or because the attempt at removal would involve too serious a risk or too serious a mutilation. In such cases, however, it may be possible to give great and prolonged relief of symptoms by an operation directed solely to the reduction of intracranial tension. This is the operation known as cerebral decompression. It has already been pointed out that the pressure effects of a cerebral tumour on the circulation in the adjacent brain substance are usually the source of its most distressing symptoms. These secondary circulatory symptoms are due to the rigidity of the skull, and can therefore be relieved by the making of an adequate opening in it. In favourable cases the relief given is immediate and very great, especially in regard to headache and vomiting and to the ocular changes (optic neuritis), which if allowed to progress cause blindness. The completeness and duration of such relief depend on the rapidity of the growth of the: tumour and on its situation. It occasionally happens, moreover, that the rate of growth of a glioma seems to be checked indefinitely by the operation.
When the situation of the tumour is known the decompressive operation should always be made directly over it; when unknown, the opening is best made in the temporal region on the right.
The opening in the skull should be of an area not less than four or five sq. in., and the dura mater exposed in it should be freely incised. The effect of the operation is due to the brain expanding freely into the opening and forming a swelling under the skin.
The relief of suffering and the prolongation of life that may with reasonable confidence he expected from a decompressive operation are such that the operation should always be used in cases where the removal of the tumour is not possible.
The function of the skull is not only that of protection but also that of support, so that after any considerable opening has been made in it the brain, if the intracranial tension has become normal, tends to become depressed, and also to undergo a good deal of movement with changes of bodily posture. Thus it comes about that the mere presence of an opening in the skull may be the cause of symptoms, and it may be necessary that the opening should be closed. This should never be done unless it is certain that the intracranial tension is normal, so that the operation is practically limited to cases in which the opening has been made for the treatment of the results of injury. The actual closure is effected by embedding some foreign material in the gap or by the use of flat bone grafts.
To avoid unnecessary detail the spinal cord may be regarded simply as the great channel of communication between the brain and the rest of the body, and the problems of spinal surgery as concerned with the way in which interruptions of conductivity through this channel can be influenced by surgical measures. Interference with conductivity at a given level will produce a corresponding impairment of function in all the parts of the body connected with the spinal cord below that level, while a complete interruption of conductivity will cause a complete voluntary paralysis and insensibility in the same parts.
The spinal cord is enclosed in a strongly walled tube - the spinal canal - lying in the spinal column and mostly made up of bone. Its seclusion within the spinal canal protects the cord very thoroughly against all ordinary violence. At the same time, however, since the size of the cord is not very much less than that of the canal, any injury whereby the walls of the latter are broken or displaced, or any abnormal substance growing within it, can scarcely fail to impinge upon the cord and damage it. These then are the two sources of impaired conductivity which come before the surgeon - injury of the spine and intraspinal swellings in the nature of tumours or inflammatory deposits.
With regard to the resources of spinal surgery it is essential that it should be understood that there is no process of regeneration in the spinal cord; any destructive damage is permanent and incapable of remedy, so that if for example a part or the whole thickness of the cord is cut across conduction is finally interrupted at the divided place, and no suturing or grafting operation can restore it. Wherein, then, it may be asked, is the field of usefulness of the surgeon ? The answer lies in the fact that conduction is frequently interrupted by pressure on the spinal cord without destruction of its substance, and in so far as an interruption is due to pressure only and has not been in existence long enough to produce secondary destructive effects it can usually be relieved and unction restored by operation.
When an injury is severe enough to break the wall of the spinal canal (falls, severe blows on the back, bullet or shell wounds), the total body of spinal cord symptoms is made up of three factors. First, shock to the cord which may abolish its functions, though there may be no corresponding gross and visible injury; this shock effect tends to pass off within a period extending to three or four weeks. Secondly, destructive injury of the cord by crushing or laceration, which in so far as it is destructive is permanent. Thirdly, interference with the cord by compression; the cord may thus be pressed on by a foreign body (bullet or shell fragment), by displaced bone of the spine, by swelling of the soft tissues (including the cord itself), from bruising, and at a later period by the results of scar formation in the injured tissues.
The surgeon has to take these three factors into account before undertaking an operation for spinal injury, and he must always remember that it is the third alone that he has any power favourably to influence. He will, therefore, necessarily wait until the shock element has passed off, and will determine this by the reappearance of reflex activit y in the cord. He will then have to decide whether the probabilities are in favour of any considerable proportion of the symptoms being clue to compression rather than to destruction of the cord. The difficulty is that there is nothing in the actual symptoms themselves to decide this, but experience shows that when very gross interruption of conductivity remains complete after the shock effect has passed off the proportion of symptoms due to the factor of compression is likely to be very small. The most hopeful field in the surgery of spinal injuries lies therefore where interruption of conductivity is manifestly incomplete.
These conditions interrupt conduction in the spinal cord by slowly developing compression, so that there is nothing in the actual state of the cord inconsistent with recovery provided the compression has not lasted too long. Complete recovery may follow the removal of a compression that has caused total interruption of conduction for several months. When the compression has lasted very long incomplete recovery is the rule. The actual lesions that may occur are as follows: (I) Malignant tumours of the bones of the spine, primary or secondary, and much the more commonly the latter. Radical removal of the tumour is impossible, and operation for the relief of the pressure it is exercising on the cord is justifiable only in very exceptional cases. (2) Benign tumours of the spinal bones (osteoma, chondroma), of the spinal membranes (endothelioma, ammoma, fibroma), of the spinal vessels (angeioma), of the nerves (neurofibroma), and of the substance of the cord itself. Radical removal of the tumour can be carried out in most cases of this class. In early cases when the operation is successful complete recovery is the rule, and the results are brilliantly satisfactory. Spinal angeioma and tumours of the cord substance are not usually removable. (3) Inflammatory swellings. Chronic localized meningitis (meningitis circumscripta serosa) produces a loculated collection of fluid in the arachnoid membrane and causes pressure on the cord in much the same manner as a benign tumour. The results of operative treatment are usually satisfactory. Tuberculosis of the spine by extension of the granuloma or of an abscess into the spinal canal frequently causes compression of the cord. If the condition persists in spite of adequate treatment of the primary disease operation may be necessary to relieve the pressure on the cord.
The application of surgery to the relief of compression of the spinal cord by disease is on the whole, then, very satisfactory. When secondary malignant disease of the spine has been shown not to be present, the surgeon is able to enter upon an operation for compression paraplegia with the practical certainty of being able to give relief and the fair probability of attaining a cure.
This department of surgery is almost wholly concerned with the repair of nerves which have been injured, and the relief of certain diseased conditions of which the principal symptom is pain. Outside of these two fields of activity the occasions on which surgery has to deal with the peripheral nerves are not many. There is only one common tumour of nerves and that is the neuro-fibroma. When this occurs on the auditory nerve within the skull or on a spinal nerve within the spinal canal its situation gives it an importance it does not in itself possess, which has already been referred to. Occurring elsewhere it is important only if it causes pain or tenderness, when it should be removed by operation.
It is only in the peripheral nerves that the nervous system possesses the power of regenerating after destructive injuries. The common form of such injury is the division of a nerve by an accidental wound or a wound of war. After such a division the essential part of the nerve beyond the seat of the injury disappears, leaving only the framework of protective and supporting tissue by which it had been surrounded. After such a divided nerve has been stitched together a new growth of nerve fibres pushes out from the original cut surface downwards into the surviving old framework, and ultimately reestablishes the functions that have been lost. This process of regeneration is by no means always fully accomplished even in favourable circumstances, and is very easily interfered with if the conditions are at all unfavourable. Favourable circumstances are that the divided ends should be sutured together early and with the proper operative technique, that the wound remain free from infection, and that the affected limb be kept in a state favourable for the resumption of its temporarily lost functions. Any deviation from these conditions greatly increases the normal uncertainties of the regenerative process. No limit, however, can be set to the time within which suture must be carried out in order to give some hope of effective regeneration. When so much of the length of a nerve has been destroyed that the ends cannot be brought together by any device short of a grafting operation, the chances of a satisfactory return of function are much reduced. In certain cases when recovery after nerve suture has failed to occur, or is extremely improbable, a limb satisfactorily useful from the motor point of view can be obtained by redistributing such motor power as remains by an operation of tendon transplantation. The maintenance of a healthy condition in the affected limb during the abeyance of function is an essential part of the treatment. The neglect of this aspect of the case may deprive a technically satisfactory operation of nerve suture of ultimate success.
The term neuralgia is used here to indicate the rather indefinite group of conditions in which pain is the sole or the wholly predominant symptom. To bring a given case within this group it must be shown that the cause of the pain does not lie outside the affected nerve. Only when this requirement has been satisfied can the appropriate surgical measures directed to the nerve be justifiably undertaken. This precision of diagnosis is indispensable, because the treatment to be used consists in the destruction by one means or another of the affected nerve, and it is plain that such a procedure would leave unaffected any condition of disease outside the nerve.
Injuries of nerves are a fruitful source of persistent pain of the neuralgic type under consideration. Any injury of a nerve is a potential starting point for neuralgia, but the division of nerves in an amputation is perhaps the commonest, especially in cases where the wound has become infected. Of neuralgias not associated with injury the dreaded trigeminal or trifacial neuralgia (tic douloureux) is the most frequent and most formidable. In both conditions three types of surgical procedure are in use - the removal of the terminal and affected part of the nerve, the injection of alcohol into the nerve above the affected part, or the division of the nerve close to its origin from the spinal cord or brain. The last-mentioned type of operation is not usually effective in the treatment of pain due to nerve injury, but it is curative in trigeminal neuralgia, and in spite of its gravity has in suitable circumstances to be undertaken.
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