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Having defined the general limitations within which the sur- geon 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.

Curative Operations. 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 ele- ment in the symptoms that may be due to destruction of brain tissue is necessarily irremediable.

(a) Operations Curative by Relief of Intracranial Tension. 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.

(b) Operations for the Removal of Extravasated Blood. 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 re- moved 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 symp- toms of haemorrhage of all kinds are due to secondary circulatory disturbance, but in so far as they are due to destructive disorgani- zation they are beyond remedy, so that while a successful opera- tion 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 accord- ing 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 situa- tions in which they arise tumours of the brain substance are gli- omas, 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 pros- pect 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 opera- tion of itself is likely to cause. Endothelioma of the membranes does not infiltrate the brain substance, and can therefore be re- moved 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. N euro-fibroma is almost confined to one situation, the auditory nerve in it's 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 favour- able circumstances, however, the operation may be satisfactory.

These three representative neoplasms if untreated necessarily cause death; the only curative treatment of them is operative re- moval; 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 pur- sued 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.

Palliative Operations. 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 mutila- tion. 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 circu- lation 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 fa- vourable 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 blind- ness. 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 be 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.

Plastic Operations. The function of the skull is not only that of protection but also that of support, so that after any consider- able 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 open- ing 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.

Surgery of the Spinal Cord. To avoid unnecessary detail the spinal cord may be regarded simply as the great channel of com- munication 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 in- fluenced by surgical measures. Interference with conductivity at a given level will produce a corresponding impairment of func- tion 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, how- ever, 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.