Arachnoid Cysts
167 Art. II.?. :Author: J. Crichton Browne, M.D., P.R.S.E. Medical Director, West Riding Asylum.
Of the pathological changes that present themselves to obser- vation in the post-mortem theatre of an asylum, there are few more striking or distinctive than those membranous bags or films that have been designated arachnoid cysts. Lining the dura mater, and covering the surface of the hemispheres, which they sometimes compress to no inconsiderable degree, they are calculated, by their situation, by their glistening surface, their variegated tints, their essentially morbid appearance, to impress and dwell in the memory. Once seen they are not easily forgotten, and once pictured in the mind’s eye by the aid of an accurate description, there can be but little danger that when thereafter encountered they might be mis- taken for anything else. Descriptions of such cysts abound in the records of most asylums, and it may be well to open -what I have to say regarding them by quoting a description from the archives of the West Riding Asylum, selected not because it is unusually precise or excellent, but because it is the first that comes to hand, and refers to the last case here in which arachnoid cysts were discovered.
H. H. died in the West Riding Asylum on the 11th of .June last, having completed the dreary curriculum of general paralysis, unvaried in his case by any exceptional incidents. The post-mortem examination of his body took place thirty-five hours after his death, and revealed the presence of arachnoid cysts on his brain. The instant that the skull was opened the presence of these cysts was suspected, for the dura mater was not so white as it ordinarily is, but had a diffused bluish tinge, and fluctuated perceptibly when touched. The reflection of the dura mater brought the cysts into view, lying upon both hemispheres, and covering what was exposed of them entirely, so that no convolution was visible. Between the dura mater and the cysts a certain degree of adhesion existed, which could, however, be readily broken down by the finger tip, except at a few scattered points over the left hemisphere, where threads of greater tenacity bound them together, requiring the point of a knife for their severance. The inner surface of the dura mater, wherever in contact with the cysts, had a rusty reddish brown colour, due to an exceedingly fine layer of deposit capable of being scraped off. The cysts themselves were quite distinct from each other, and that on the left side was much the larger of the two. It formed a large membranous bag with fluid contents, and it not only covered the upper aspect of the hemisphere, but was wrapped round its edges and ends, and continued as a toughly glutinous layer over the orbital lobule to the middle sulcus, and over the whole contour of the tempero-sphenoidal lobe. In colour it varied from a dull buff over the parietal eminence to a pale pink at its outer margins, dabbled with sanguine blotches, and with irregularly interspersed greenish and brownish tints. In its walls, which were smooth and moist, ramified minute vessels, and in its interior were several ounces of clear fluid of a greenish red colour. This fluid occupied the cavity of the cyst, which was co-extensive with the parietal and posterior portions of the frontal lobe. Beyond these limits the two layers of the cyst became adherent, though for some distance they could be torn asunder. Ultimately, however, towards the base of the brain, they became intimately and inseparably connected, and formed one delicate membrane of the consistence of the most toughly organised clots found in the cardiac cavities. The cyst covering the right hemisphere in all respects resembled that on the left side, except that its walls were everywhere thinner, and that it contained a less amount of fluid. When the two cysts were removed from the hemispheres, from which they could be readily peeled off, being only adherent by a few reddish threads (blood vessels) binding them to the arachnoid and pia mater beneath, the brain was seen to be generally flattened and compressed. The convolu- tions looked as if they had been smoothed out, and the sulci were scarcely discernible. This was especially the case on the left side, where the compression of the brain was most marked, the frontal lobe having an attenuated and pointed appearance. Beneath the cysts, the visceral layer of the arachnoid, opaque and milky in some places, was distinctly seen, and beneath it was the pia mater, intimately adherent to the cineritious matter of the gyri. A few of the gyri on the left side?the ascend- ing parietal, postero-parietal lobule, and angular gyrus?pre- sented an unusual appearance, the outer surface of their cortical matter being stained of a deep reddish yellow or mahogany colour. This staining, unlike the adhesions of the pia mater, was not confined to the summits of the gyri, but dipped down along their sides, even to the bottom of the sulci. When removed from the brain and emptied of their fluid contents, the two cysts weighed exactly 39 grammes.
In this case the arachnoid cysts were of great size and extent, and belonged, indeed, to the most marked type of these morbid formations which are seen in other cases of very varied dimensions, but all partaking of the same characters. Even in those cases where the reparative process has advanced furthest in the removal of the cysts, they are found as thin, transparent, cloudy membranes, investing the frontal or parietal lobes, separable towards the middle into two layers, perhaps closely applied, or even adherent to each other, but continued as one attenuated membrane towards the periphery.
Arachnoid cysts are, as I have said, perhaps the most striking, and they are certainly not the least frequent, of the intra-cranial pathological appearances found on inspection of the bodies of the insane. I have carefully gone over the reports of 1,240 post-mortem examinations performed under my own supervision in the West Eiding Asylum during the last nine years, and I find that in exactly 59 of these cases were arachnoid cysts discovered. The induction is sufficiently large to warrant the conclusion that such cysts exist in nearly 5 per cent, of all lunatics dying in asylums. In the 59 cases I have of course included cysts in every stage of development, and all sub- arachnoidal haemorrhages, except such as were connected with clots in the cerebral substance, and were really dependent upon the breaking out of the clot on the surface of the brain or on the escape of blood from the ventricles. Wherever extravasa- tion of blood had taken place into the arachnoid cavity, whether that extravasation had become organised or not, I have con- sidered the case one of arachnoid cyst, and have embraced it in my statistics. The cases, however, in which the extravasa- tion was of recent origin, and remained as a film of fluid blood or a simple clot, were only 11 in number, leaving 48 cases in which a membranous formation and persistent sac had taken the place of the original coagulum. The 11 cases, too, in which the cysts were in their incipient stage all presented features making the true character of the sanguineous effusion into the arachnoid quite unmistakable.
Of the 59 patients in the West Eiding Asylum in whom arachnoid cysts were shown to exist on post-mortem examina- tion, 43 were males and 16 females, so that the liability of the male sex to this particular pathological change seems to be nearly three times as great as that of the female sex. The explanation of this singular disparity is to be sought in the much higher liability of males to suffer from those serious organic diseases of the cerebrum upon which as a rule arach- noid cysts supervene. The following table shows at a glance the diseases and degenerations which afflicted and caused the death of those 59 patients in whom arachnoid cysts were recorded:?
Disease Hale Female Total General paralysis of the insane Chronic disorganisation of the brain Senile atrophy of the brain Epilepsy, with domentia . Chorea, with mania . Meningitis, with mania . Bright’s disease, with mania Phthisis, with chronic mania
26 11 3 1 1 1 29 16 4 3 2 2 2 1 Total 43 16 59
We thus see that in nearly one-half of the whole number of cases in which arachnoid cysts were found general paralysis was the disease causing death, and that in every case, there is reason to suppose, there was antecedent degeneration of the brain or its blood-vessels. The ages at the time of death of the patients in whom the morbid change under consideration existed correspond of course with those periods of life in which organic diseases of the brain and its membranes have their maximum frequency. As is shown in the accompanying- table 28, or nearly one-half of the whole number of arachnoid cysts, were found in patients dying between the ages of 35 and 45. A distinction is thus pointed out between arachnoideal haemorrhages and those taking place in the substance of the cerebrum, which have their maximum frequency at a much later period of life.
Age Male Female Total Between 20 and 30 . 30 ? 35 . 35 ? 40 . 40 ? 45 . 45 ? 50 . 50 ? 55 . 55 ? 60 . 60 ? 70 . 70 ? 80 . 17 6 3 6 4 2 2 2 2 20 8 6 10 6 3 2 Total . 43 16 59
As to the localisation of the cysts, I find that in 14 of the 59 cases the cyst covered the left hemisphere, in 13 the right hemisphere, while in 32 cases there were cysts over both hemispheres- Although it might seem from these figures that the two hemispheres are liable to be affected by arach- noid cysts in about equal proportion, there is other evidence indicating that the left side of the encephalon is the more chosen habitat of that particular morbid change. In 8 of the 32 cases in which cysts were spread over both hemispheres it is noted that that on the left side was much the larger and fuller of the two, whereas in only 1 case of the 32 is there a record that the right cyst exceeded the left one in size. Then in the 14 cases in which the cyst was limited to the left side the descriptions given unmistakably show that the pathological condition was more pronounced than in the 13 cases in which the right side was affected. It was in those 14 cases that the most decided instances of wasting of the hemisphere com- pressed by the cyst occurred. Thus in J. M. the left hemi- sphere, which had been enveloped in a cyst, weighed 470 grammes, while the right, which had not been so enveloped, weighed 595 grammes. In Gr. L. the left hemisphere, which had been cyst-covered, weighed 528 grammes, and the right, which had been free, weighed 570. On the other hand, in the cases in which cysts were found on the right side alone the difference in the weight of the two halves of the cerebrum was com- paratively trifling.
Respecting the mode of origin of those cysts found in the arachnoid cavities, I have already taken for granted the truth of the proposition that they result from extravasations of blood. The writings of Mr. Prescott Hewett, Dr Ogle, Dr. Wilks, Dr Henry Sutherland, and of other able observers, may be almost said to place that truth beyond cavil. The old theory that these cysts originated in the organisation of lymph poured out during an anachritis has now few supporters. The cysts have been seen in every stage * of their formation?from fluid blood up to tenacious membrane, and light has been thrown on their nature and structure by experiment and the study of various allied conditions. Thus Sperling (’ Centrall.’ 1871, 448) has made injections between the dura mater and the arachnoid over the convexity of the brain in rabbits with the following results :?Eight days after the injection of fresh blood it began to be organised into a connective-tissue mem- brane, which was complete after two or three weeks. After the latter period new blood-vessels were found in the new mem- brane, which agreed in all characters with the membrane of pachymeningitis. The organisation of the blood occurred over the convexity of the brain on the inner surface of the dura mater without any adhesions to the arachnoid. The formation of the new membrane was due to the organisation of the fibrin contained in the blood. That this was so was shown by the fact that no new formation was found after the injection of defibrinated blood, which was completely re-absorbed. Injections of iodine and other irritating fluids was not followed by any new formation. In some cases the dura mater was found thickened, in others there was pus. Then in the ceph al- ii asmatoma of infants we may discern an analogous origin and a series of analogous changes to those which take place in the intra-cranial hsematomata of adults.
It is no uncommon occurrence to find in the infant whose head has been subjected to severe and long-continued pressure during parturition, by the os uteri or against the walls of the pelvis, large extravasations of blood both without and within the cranium. The pressure to which the infant’s head has been subjected has bruised its tissues, and the difficulties con- nected with the establishment of a new current of circulation and a new respiratory process have interfered with the free return of the blood from the cephalic vessels, as the tumid and livid features seen at such a time abundantly testify, and so a capillary hemorrhage or oozing takes place. If the extrava- sation be within the cranium and be of considerable amount, death, preceded by coldness of the surface, laboured breathing, slowing of the pulse, and muscular twitchings or convulsions, takes place. If it be within the cranium, but of less amount, a false membrane is formed, the cerebrum is compressed and restricted in growth, and incurable idiocy results. And if it be within the cranium, and of still less amount, it may be altogether absorbed and produce no unpleasant consequences. If, on the other hand, the extravasation be without the cranium, little or no danger attends it, and facilities are offered for watching its formation and the changes which it undergoes. Under such circumstances it first becomes perceptible within a few hours of birth, on one or both of the parietal bones, as an elastic fluctuating tumour, which goes on slowly enlarging for several days, until it sometimes attains the size of an orange. When it has reached its full dimensions the cephal- hematoma?for so the tumour is designated?remains stationary for some time, and then retrogrades in a definite manner. A ring of hard consistence forms at the circumference of its base, the clot separates into serum and crassamentum, the latter is gradually deprived of its colouring matter, a steady diminution in size goes on, until complete absorption has taken place. For long, however, after the cephalhematoma has dis- appeared, a slight elevation may be found at the site which it occupied.
In the othsematomata of the insane a connecting link may be found between the cephalhcematomata of infants and the arachnoid cysts of chronic lunatics. These othsema- tomata have been shown to depend on an accumulation of blood between the skin of the pinna and the cartilage, gradually increasing until a high state of tension of the covering is reached, and then retrograding by the formation of a coagu- lum, the adhesion of a membrane to the walls of the sac, and the steady absorption of its liquid contents, until only a few fibrous shreds and some cholesterine are left at its core. The different stages of growth and retrocession in the blood tumours of the ear agree closely with those which take place in the blood tumours beneath the dura mater, except that in the case of the ear tumours there are certain special subsequent changes attributable to degeneration and shrivelling of the cartilage, the nutrition of which had been seriously interfered with by the extravasation. In all blood tumours, in fact, the process of growth and decay is tolerably uniform. The sangui- neous effusion is gathered into a clot or disseminated into a layer. It forms a coagulum, enclosing the fluid portions of the blood, that coagulum is absorbed or becomes condensed and organised, with vessels ramifying in it, and then it remains stationary or dwindles away, according to its surroundings. The mode of origin of arachnoid cysts in the manner indi- cated is now almost universally admitted, and the point to be determined is not whether these cysts are hgemorrhagic in their source, but whence the hemorrhage has taken place. By some it is maintained that it proceeds from the ruptured vessels of a false membrane or efflorescence lining the dura mater, and resulting from a pachymengitis, and by others that it has its source in the vessels of the dura mater itself. But neither of these views seems to me to be satisfactory. The few and slender vessels which penetrate the dura mater from its outside, where its great vascular supply is situated, are incapable of pouring out so large a quantity of blood as frequently goes to the forma- tion of a cyst; and this will be especially evident when it is borne in mind that these vessels?the vctsa propria of the mem- brane?have a singular proclivity to become plugged by coagula, and so sometimes induce gangrenous changes in areas of paren- chyma thus cut off from nourishment. Then, as to the alleged false membrane of the dura mater and its bleeding capillaries, it is to be remarked, that in many cases where the cysts are largest no such membrane nor any reminiscence of it, nor any extraordinary thickening of the dura mater has been discover- able ; and that in other cases, where a gauzy shreddy lining of the dura mater, distinct from the cyst, has been discerned, its vessels also have seemed inadequate to the production of such a haemorrhage as that which goes to the making of an arachnoid cyst. The capacity of the newly developed capillary network in the way of extravasating blood may, perhaps, be gauged by the bloody points and blotches which are often seen in its sub- stance, and which do not exceed a sixpence in circumference or thickness. The gap between these blotches and an arachnoid cyst is certainly very wide. Even allowing that the capillaries in such a membrane are very capacious, and are distributed in young and lax connective tissue, and that they are, as has been said, a diverticulum or safety-valve for the increased tension of the actively congested dura mater, it is still impossible to admit the conclusion sought to be drawn from these facts, that they may, by interstitial htemorrhage, create those masses and extensive layers of clot that are transformed into arachnoid cysts. If arachnoid cysts were really derived from such efflor- escences, we should expect to find them formed most frequently at the time when the circulation in the new membrane was most active, when the pacliymengitis was at its height. But the fact is, that we never do find such cysts in cases of general paralysis or other brain disease in its early stages, when in- flammatory changes might be supposed to be most energetic. I have never encountered such a cyst or its preparatory clot in any general paralytic carried off by intercurrent disease earlier than the second stage of the malady. Arachnoid cysts are consequential and not essential changes in all the diseases in which they occur. As a rule, too, they do not begin to form until the disease has well-nigh run its course. And here we have a clue to their point of origin. If these cysts never appear until the disease is far advanced?until much wast- ing of the brain has taken place?it is fair to infer that they are drawn from some of the vessels which become over-distended when wasting is established. And the vessels which suffer most in this way are the great veins which run over the frontal and parietal lobes, conveying the blood to the longitudinal sinus. These become terribly dilated and engorged, and at the same time, being to a great extent surrounded by serous fluid, they have lost some of that support which they normally derive from the subjacent brain-substance. Then they are also in a state of permanent atony brought on by the protracted and often- repeated irritation and hyperemia of the cineritious substances of the brain in general paralysis and kindred complaints; and this state, through passive congestion and plilebectazy, distension and elongation, may lead not merely to effusion of serum and oedema of the pia mater, but also, on the occurrence of any determining cause, to actual haemorrhage. This will be parti- cularly likely to happen when the delicate walls of the veins are degenerated as well as stretched and dilated, as it is not impro- bable they are in many organic cerebral diseases. All this being so, it appears that the veins of the pia mater are, under certain circumstances, very liable to rupture; and the calibre of these veins is such that they could furnish forth the smallest and the largest of the superficial clots that are found on the surface of the brain. It is certainly an instructive fact in rela- tion to their origin, that the largest of these superficial clots invariably have their centre and thickest part precisely at those sites where wasting is always most decided and where the veins are most distended, that is to say, in the upper frontal and parietal regions.
It is scarcely to be expected that’in such haemorrhages as those into the arachnoid cavity the precise point of leakage should be detectable. If the hsemorrhage is of any age at the date of the examination the damage may have been repaired; if it is quite recent there are generally revealed by its removal a large number of oozing points in the vessels, from any- one of which it might have originated. In one case, however, which came under notice in the West Riding Asylum some years ago, conclusive evidence was obtained that an extravasa- tion into the arachnoid cavity may come from the great veins. True in that case the pathological conditions displayed were somewhat unique; but the significant fact remains that the blood poured out had flowed, not indeed from the veins of the pia mater, but from their confluence in the sinuses of the dura mater. The patient was a woman 53 years of age, who had laboured for above four years under chronic mania, and who was steadily losing health. While passing through an exacer- bation of excitement in December 1871 she suddenly, in the midst of a transport of shouting, became silent, pale, and faint. Taken to bed, she grew drowsy and stupid, and in twelve hours was in a state of deep coma, which continued for four days, and then ended in death. At the inspection of her body a large dark pulpy clot, about an eighth of an inch in thickness, was found lying upon the surface of the brain on the left side. It covered the tempero-spheroidal lobe, and extended backwards on to the occipital lobe, and upwards on to the parietal lobe. On removing the mass of the clot several small stringy clots of considerable tenacity were found proceeding from it into several small distinct holes or deficiencies in the left lateral sinus. Out of these holes the tenacious clots could be dragged, leaving patent communication with the cavity of the sinus. There were three such holes distinctly visible, and a few smaller and less distinct ones. The dura mater, where forming the left lateral sinus and in its vicinity was thin, and had a singular reticulated appearance. It looked as if it were almost cribriform, as if it had been macerated and the bundles of fibres composing* it had been dissected out and separated from each other. Along the superior longitudinal sinus there were several reticulated attenuated-looking patches resembling those seen over and about the lateral sinus.
Cases have been reported in which, from traumatic causes, the veins of the pia mater have been altogether torn away from the superior longitudinal sinus, and no difficulty need, I think, be experienced in conceiving liow minor injuries of these veins, or their rupture from extreme distension, may permit the formation of large superficial clots and arachnoid cysts. Dr Wilks, than whom no higher authority could be quoted upon such a subject, has expressed his belief that the effusions of blood which give rise to arachnoid cysts may proceed from a laceration of a vessel of the pia mater.
It has been generally alleged that the effusions of blood which give rise to arachnoid cysts result from blows or injuries, and no doubt much may be said in favour of that theory. These cysts are mostly found in patients who have suffered from diseases characterised by diminished precision of muscular movement and loss of the power of equilibrium, and characterised also by restlessness and reckless excitement, so that it might well be that in such cases falls and concussions of the brain have been sustained. My own observations, however, have led me to believe that in reality blows and injuries play a comparatively insignificant part in the causation of arachnoid cysts, and that other conditions are more generally responsible for their produc- tion. Allowing at once the impossibility of proving that blows have not been instrumental in their production, particularly when the recollections of the patient himself are not available as evidence, I may still instance cases which have fallen within my own knowledge, which had been carefully watched from first to last, in which no accident of any kind had been known to have taken place, and in which these cysts were discovered post mortem. I have found these cysts in their incipient stage existing, indeed, as a dark soft clot of blood, obviously formed only very shortly before death, in patients who had been bed- ridden and incapable of spontaneous movement for weeks prior to their decease, during which they had been watched uninter- ruptedly, and who presented no vestige of a bruise or injury upon the scalp or any other part of their bodies. One very instructive case bearing upon the point at issue occurred in my practice some years ago. A patient well advanced in general paralysis, but without any muscular symptoms except thickness of speech and tremor of the face, was seized by epileptiform convulsions in my presence. He was seated at the time when the convulsions came on, and did not fall, but was at once supported and conveyed to bed, where he continued to suffer from general chronic spasms for twenty-four hours, his head, face, and neck being livid, congested, and bathed in perspira- tion throughout the seizure. After the convulsions ceased he remained in a drowsy, semi-comatose state for nearly a week, and then it was ascertained that he had, to a great extent, lost power in his right arm and leg. This condition of partial hemiplegia was subsequently in some degree mitigated, but it never entirely disappeared until his death, which happened two months after the first and only epileptiform attack from which he had suffered. At the sectio cadaveris a pulpy mem- branous clot, decolorised at its centre and containing there a cavity with fluid contents, was found stretched over, the upper surface of the left hemisphere, upon which it exercised con- siderable pressure. I think it is reasonable to infer that that clot or arachnoid cyst was formed during the epileptiform seizure, and was due not to any external violence, but to the over-distended state of the intracranial vessels during the long-sustained con- vulsive condition.
Bearing in mind that towards the close of general paralysis, and other organic diseases of the brain accompanied by wasting, the vessels are dilated, are deprived of their proper support, and are also badly nourished and degenerated, it is not difficult to understand that many other circumstances besides the jar of a concussion may lead to their rupture and the effusion of their contents. No doubt a sudden and violent vibration may and does sometimes bring about that catastrophe, but what I desire to insist upon is that there are many other agencies which are at least equally potent in inducing it. Any circumstance or condition that occasions cerebral hyperemia may be re- sponsible for its occurrence. And such circumstances and con- ditions are certainly not wanting in patients of the class liable to arachnoid cysts. They labour under a great tendency to faecal accumulations in the intestines, and these, by compressing the abdominal aorta, are particularly apt to cause cerebral conges- tion. They are rash and careless in their conduct, and often expose the skin to cold, and so set up collateral fluxionary congestion of the encephalon. They are often sedentary in their habits and voracious in their appetites, and so grow fat and plethoric for a time after the cerebral disease has spent its earliest force, and are thus again exposed to risks of hyper- emia of the brain. They are subject to transient attacks of mental excitement, during which there is active liypersemia of the cortical substances of the brain, and in which they shout and strain, and so hinder the return of blood to the thorax, and aggravate the cerebral congestion. And they are subject also to epileptiform attacks, often of great severity, in which there are trachelismus, fixture of the respiratory muscles, and an intense degree of engorgement of all the blood-carrying conduits of the head. In one and all of these conditions there is surely enough to account for arachnoid cysts in many cases without resorting to the crude hypothesis of mechanical disturbance. Were these cysts in many instances due to blows or falls we should certainly expect to find associated with them occa- sionally some of the other and more ordinary consequences of injury of the head of such severity as to cause the rupture of a vessel. Now, it is a remarkable fact that I have never in such cases seen a trace of hemorrhage outside the dura mater, although, as is well known, the meningeal vessels are most of all apt to give way when violence is applied to the head. It is remarkable, also, that I have never been able to detect any damage to the skull, any rupture or softening of the cerebral substance, or any remains of those changes which are most familiar as the results of injuries of the head. On the other hand, again, it is curious that in cases in which undoubted injuries have occurred to the head arachnoid cysts are very rarely encountered, save in general paralytics and other patients, with organically diseased brains. From all which it must, I think, be deduced that an error has been committed in attri- buting all arachnoid cysts to traumatic causes, and that we shall be justified in holding that many of them are ascribable to the spontaneous laceration of a vessel, owing to morbid changes and conditions. Such spontaneous laceration we see taking placing in hooping-cough, and also in those very diseases upon which arachnoid cysts supervene in the otheematomata (to which we have already adverted) of the external ear, which were also at one time held to be invariably the offspring of injury, but which are now known to grow up without the intervention of any outward force. It seems to me that the old formula that injuries of the head affect the surface of the brain and diseases its interior is no longer tenable, and that for practical and medico-legal purposes we are bound to depart from the notions which have long been promulgated about arachnoid cysts, and to maintain that they may and frequently do originate in what is called a spontaneous manner.
To the interesting enquiry that arises whether there are any distinctive symptoms making it clear during life that an arach- noid cyst has been formed, and making it safe to predict that one will be found after death, only an uncertain answer can be returned. A priori, one should have thought that such a for- midable-looking lesion in so infinitely important a position would have been attended by unmistakable outward signs, and indeed, when looking at a large cyst one cannot help wondering that life was for any length of time compatible with its presence within the cranium. The fact is that such an extravasation occur- ring in a previously healthy man would inevitably cause speedy death, and that it is only tolerated in those diseased persons in whom it is found because they have been prepared, as it were, to receive it and to sustain its effects. The grey matter of the cerebrum is exceedingly liable to alteration under various con- ditions, and in certain states of alteration is able to adapt itself to circumstances that in its normal state would prove fatal. In the undeveloped brain large clots are borne with impunity, and MM. Eilliet and Barthey have pointed out that in infants copious and widely diffused extravasation of blood may exist on the surface of the hemispheres without any paralysis being- present. Well, in the involuted brains of chronic lunatics a> similar insensibility exists. The degenerated, or partially dis- integrated, cerebral matter is far less susceptible to the influence of compression and irritation than it was in those days when it rejoiced in the plenitude of its power. An amount of com- pression that would at once arrest the functions of a vigorous, brain and interrupt consciousness may exert but little effect on the sluggish movements of one that is already dilapidated and may scarcely augment the helplessness of dementia. The de- generated brain is already, owing to changes in its vessels and the surrounding textures, in a state of anaemia, and cannot therefore have its blood squeezed out of it by compression to the same extent as takes place in a healthy brain in the fulness of its vascular supply when similarly treated. Therefore it comes about that in general paralysis and organic dementia the indications afforded of a superficial haemorrhage on the brain are sometimes very insignificant, especially if the haemorrhage has taken place slowly. These indications consist in some slightly increased impairment of muscular power on one or both sides of the body, and in some further deepening of the already profound fatuity, and cannot of course warrant more than a suspicion that a superficial haemorrhage has taken place. In some cases, however, there are other symptoms which may convert a suspicion into tolerable certainty, and which may even enable us to fix upon the precise time when the haemorrhage occurred and the foundations of the cyst were laid. In a case already quoted, it was tolerably clear that the haemorrhage took place during an epileptiform seizure, and in several other cases, of which I possess notes, the symptoms suggest forcibly that the clot was formed under similar circum- stances. One case may be mentioned which proves incon- testable” that extravasations of blood do occur on the surface of the brain during the convulsive seizures of organic cerebral disease. M. L., female, aged 38, was sinking quietly through the final stage of general paralysis of four years’ duration, when, on April 25th, 1873, she was seized by convulsions, which recurred frequently on that and the following day. The con- vulsive movements were sometimes on one side of the body, sometimes on the other, and occasionally bi-lateral. They affected, however, chiefly the left side of the body, the head being turned as if looking over the left shoulder. On the second day it was noted that, during the intervals between the convulsions, she lay with her head slightly turned to the left and that she was incessantly going through a chewing move- ment ; she endeavoured to bite everything that was brought near her, and when nothing else was available she gnawed her own hair and the bedclothes ; she was only partially conscious. She continued in much the same state up till the 6th of May, when she died. At the post-mortem examination, six small dis- tinct dark clots were found under the arachnoid, in the meshes of the pia mater, lying upon the three tiers of frontal gyri of the right side. These were quite recent and quite superficial. All the vessels of the pia mater were engorged with dark blood. In another case the formation of the clot at a much longer period before death was indicated with tolerable clearness. S. A. S., a female, aged 46, who was suffering from severe chorea-mania, went to bed in her usual condition at 7.30 p.m. on the evening of October 24th, 1873. An hour later she was found by the night-nurse apparently dead: her features were pallid, and there were no respiratory movements beyond a few convulsive twitch- ings in the throat. Artificial respiration had to be kept up for some time before she revived. For many hours she remained in a stupid bewildered semi-comatose condition, and when this passed off she was still decidedly more fatuous and feeble than she had previously been, drooping perceptibly to the left side. She grew worse and died from typhlitis in the February follow- ing, when a thin reddish yellow membrane of considerable tenacity was found spread over the right hemisphere, having its centre in the parietal lobe.
The commencement of the clot in an attack of excitement was illustrated in the case of T. E., aged 36, an inmate of the West Riding Asylum. This man, who was a general paralytic, had improved slightly under Calabar bean, when, on October 11th, 1875, he had an unaccountable outburst of excite- ment, in which he shouted, stamped, swore, and behaved with great violence. His fury, however, gradually became more impotent, and lie passed into stupor. On the following day liis eyeballs were prominent, his pupils were unequal and irregular in their margins, his face was flushed, his gait was very unsteady, and he was torpid and could not speak. Sub- sequently he failed rapidly, and died on April 22, 1875. Over the left hemisphere of his brain was found a thin membrane, separable into two layers and pretty firmly adherent to the dura mater.
As to the treatment of arachnoid cysts not much can be said, as they scarcely admit of treatment apart from the diseases of which they are complications. The great matter is to guard against their formation. If we knew that blood was actually being poured out into the arachnoid, we might, perhaps, limit the amount of the extravasation by ergotine and active purgatives. When, however, the extravasation has once taken place not much can be done beyond improving the general health, so as to favour absorption. Iodide of potassium has been tried, but with doubtful benefit.
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