The frequent discovery of tears of the dura mater septa associated with subdural cerebral haemorrhage, in foetuses dying during the course of labour, was one of the most striking features of this investigation. Out of 168 fresh foetuses the tentorium cerebelli was found torn in 81 (48 percent.), associated with tearing of the falx cerebri in five cases and with subdural cerebral haemorrhage in all but six. Most were the result of breech or forceps delivery, or of delivery through a contracted pelvis, but a few resulted from apparently normal labour. (These cases, with their more important details, are arranged in the table at the end.)
I am convinced that a proper understanding of the events which lead to these injuries, and of the manner in which they arise, will enable many cases of them to be avoided and foetal mortality to be correspondingly reduced. I propose, therefore, to discuss at some length the forces which act on the foetal head and the injuries they produce in the intracranial contents. In other words, to consider the stress to which the head is subjected and the strains from which it suffers.
The subject will be dealt with according to the following plan :
I. On some points in cranial mechanics.
(a) A general consideration of cranial stresses and strains.
(b) On alteration in the shape of the head, or moulding.
(c) On the effect on the dura mater septa of alterations in the shape of the head.
II. On the anatomy of the dura mater septa, especially as regards the presence of stress-bands and stress-lines.
III. On the morbid anatomy of tears of the septa as found in 81 foetuses.
IV. On the mode of origin and source of subdural cerebral haemorrhage.
V. Clinical part : analysis of the 81 cases.
I. ON SOME POINTS IN CRANIAL MECHANICS.
(a) A General Consideration of Cranial Stresses and Strains.
During its passage through the birth-canal the foetal head is subjected to the action of compressive forces, which are the resultant between the powers of labour and the resistance of the maternal passages. The head is therefore in a state of stress during labour, and this state maybe conveniently termed « cranial stress. »
Cranial stress is a compound compressive stress which may be roughly regarded as consisting of two elements : (1) a general compression of the whole head, and (2) a simple longitudinal compression by opposite forces acting at the ends of the long diameter of engagement of the head in the pelvis. It is this element of simple longitudinal stress which is of such special importance in its effects on the cranium and intracranial contents, and which is chiefly responsible for alteration in the shape of the head and stretching of the septa of the dura mater.
As the head may engage in any diameter lying between extreme flexion and extreme extension, this longitudinal stress may occur in one of many directions, but as regards their effects on the head these directions may be resolved into two (1) antero-posterior, along the diameters lying between the occiput and the forehead, as in vertex and breech presentations ; and (2) vertical, along the diameters lying between the vault and base of the cranium, as in face and brow presentations.
It is obviously impossible, during the course of labour in any given case, to analyse the exact nature of cranial stress, to measure accurately its intensity, or to predict its effects. For practical purposes no more can be said than that the stresses and their effects vary chiefly with (1) the absolute amount of the forces acting on the head at any given time, (2) the direction in which these forces act on different parts of the head, (3) the degree of plasticity, or ductility, of the head, and (4) whether the forces attain their maximum suddenly or gradually. The only means of estimating the intensity of cranial stress is by observing its effects after birth. Cranial stress may be normal or excessive ; even in the easiest labours the head is, of course, subjected to a certain amount of stress.
Normal stress leaves no observable effect, or merely a moderate alteration in shape ; excessive stress results in an excessive degree of moulding, or, as I shall show later, in the infinitely more important effects of overstretching and tearing of the tentorium cerebelli and falx cerebri, and rupture of certain blood vessels. Tearing of the tentorium and falx is clear evidence of excessive cranial stress and forms the best and simplest means of estimating, post-mortem, the degree of stress to which the head has been subjected. Excessive cranial stress is responsible for foetal death to an extent hitherto little suspected.
On the Effects of Cranial Stress. The effect of stress is strain. Without entering into a technical discussion on strain, it may be stated that all strains can be analysed into (a) slides or shearing strains, (b) stretches. A slide consists in the change of shape of a body without change of size, the familiar illustration of which is to change the shape of a book from a rectangular to an oblique shape by pressing against the long edge of one of its covers. In foetal heads which have been subjected to stress, both these classes of strain may be found ; the moulding of the foetal head is an example of a « slide » and the tearing of the septa of the dura mater is an example of a » stretch ».
The effects of a given stress on a body depend, of course, on the material of which it is composed and on its construction. If we now consider the foetal head as a body exposed to stress, and try to analyse the possible strains, we are at once faced by the extreme complexity, not only of the materials which compose it, but of its construction. It consists of a non-rigid shell, of a peculiar shape, composed of loosely-joined plates of pliable bone jointed on to a rigid base and strengthened by the attachment of the dura mater and its system of septa ; the contents of this shell are partly solid and partly fluid. Further, these contents do not lie in an absolutely closed space, for a certain amount of blood and cerebro-spinal fluid can be squeezed out of it, and the termination of the hind-brain can be crowded clown through the foramen magnum.
Even were it possible, it is not my intention to discuss the behaviour of all this complexity under stress. I shall confine myself to three specific points in the structure of the head.
These are (1) its plasticity, depending on the degree of ossification of the cranial bones, (2) the attachment of the septa of the dura mater to the cranial bones, and (3) the connection with the septa of certain blood-vessels. On these structural features depend the production of the two special strains which form the subject of this section of my report, viz., stretching and tearing of the tentorium cerebelli and falx cerebri and the rupture of certain cerebral blood-vessels. The sequence of events may be summarised as follows :
The first effect of stress is alteration in the shape of the head, or moulding ; this necessarily involves alteration in the position, absolute and relative, and curvature of the cranial bones. This movement of the bones is simultaneously transmitted to, and is resisted by (this is important to appreciate), the attached septa of the dura mater, which appear to form a mechanical system especially arranged to limit the movement of the bones forming the cranial vault, and to resist a dangerous degree of alteration in the shape of the head. The resisting septa become tense and stretched and altered in position and direction. Overstretching results in tearing, the most common site for tears being in the tentorium cerebelli at its junction with the falx cerebri. Finally, these changes in the septa are transmitted to the vein of Galen, whose fixed point is at the apex of the tentorium cerebelli ; this vein becomes stretched, kinked, and engorged, so that either itself or some of its tributaries are ruptured, resulting in subdural cerebral haemorrhage of greater or lesser extent (Refer to Fig.1).
Fig.1 (case 78) : Incomplete tear of tentorium cerebelli on right side ; the tear is across the fibres at the base of the anterior vertical band. The head shows extreme moulding after labour with generally contracted pelvis. Note elevation of apex of tentorium and change in direction of vein of Galen and straight sinus.
These deductions are based on evidence gained by the study of (1) the mechanical construction of the foetal head, especially the system on which the septa of the dura mater are arranged, the disposition of their strengthening bands, their connection with the cranial bones and the way they are influenced by alterations in the shape of the head ; and (2) the injuries to the septa and blood-vessels found in the case of foetuses whose heads have been subjected to excessive stress during labour. The remainder of my paper consists in the elaboration of these points.
(b) On Alteration in the Shape of the Head, or Moulding.
I have stated that moulding of the head is essentially an example of a slide or shearing strain, and is brought about principally by the action of compressive forces acting at the ends of the long diameter of engagement. (It is not strictly correct, however, to state that the head does not change in size ; there is probably a decrease in volume, brought about partly by the squeezing out of some blood and cerebro-spinal fluid and partly by the crowding down into the foramen magnum of the termination of the hind-brain. Evidence of such decrease in volume may be seen in the compensatory overlapping of the bones of the vault. I wish to emphasise that any decrease in the volume of the head by these means can be so slight as to be, for practical purposes, negligible. The alteration in shape is the ail-important factor.)
Alteration in shape is brought about partly by a displacement of the bony vault as a whole and partly by bending of the individual bones which compose it. The displacement of the bones as a whole takes place chiefly at the junction of the plate with the base of the occipital bone; this hinge-joint allows a considerable range of movement backwards and forwards.
The greatest bending of individual b on es occurs in the parietals and frontal ; the occipital bone is more rigid and, although it becomes bent to a certain extent, confines itself chiefly to the role of moving backwards or forwards on the occipital hinge, carrying with it the rest of the vault. The vault of the skull is plastic as a whole and can, within limits, change shape in most directions, but alterations in the shape of the head are chiefly dependent on the backward or forward movement of the occipital plate at the occipital hinge; bending of the bones is secondary to this, and is, of course, a very necessary accompaniment.
According as to whether the forces acting on the head force the occipital bone forwards or backwards, alterations in the shape of the head may be divided into two groups, (1) decrease in antero-posterior measurement, (2) increase in antero-posterior measurement.
Decrease in antero-posterior measurement is brought about by pressure applied at the opposite ends of the diameters lying between the occiput and forehead, i.e., suboccipito-bregmatic, suboccipito-frontal, and occipito-frontal ; such pressure occurs during labour in vertex presentations and in the after-coming head in breech-presentations, and is correspondingly increased when the pelvis is contracted. Decrease in antero-posterior length is naturally accompanied by a compensatory increase in vertical height ; in this form of moulding the chief change is a displacement forwards of the plate of the occipital bone, accompanied by arching of the vault of the head along the sagittal suture and free bending of the parietal and frontal bones. This is illustrated in Fig. 2 (II).
Fig 2 : Diagrammatic outlines or head and septal system or dura mater. The lines representing the septa show their chief directions of strength. (A) falx cerebri ; (B) middle (vertical) part of tentorium cerebelli ; (C) line of junction of tentorium and falx ; (D) interior (horizontal) part of tentorium cerebelli ; (E) base or skull. I. Normal shape of head. II. Shape of head during compression in occipito-frontal diameter ; greatest strain on vertical part of tentorium. III. Shape of head during compression between vault and base ; greatest strain on horizontal part of tentorium.
Increase in antero-posterior measurement occurs when the head is compressed between the base of the skull and the vault, as in face and brow presentations. The chief change is a displacement backwards of. the plate of the occipital bone, the vault of the skull becomes flattened, and the forehead is made protuberant by bending of the frontal and parietal bones. This is illustrated in Fig. 2 (III).
c) On the Effect on the Dura Mater Septa of Alterations in Shape of the Head.
It is probable that, normally, the septa are in a state of rest and are nowhere in a state of positive tension or slackness. When the head undergoes changes in shape, alterations in the tension of the septa are inevitable, owing to the nature of their attachments to the cranial bones. The behaviour of the septa is easily demonstrated by the following observations.
Take a foetal head, reflect the scalp and remove sufficient of one parietal bone to allow the corresponding cerebral hemisphere to be removed and the septa to be viewed from that side. Now compress the head in the occipito-frontal diameter so that the head is shortened antero-posteriorly by the forward displacement of the occipital bone, and heightened vertically by the elevation and bending of the vault (refer to Fig.1). At the same time observe the septa. The middle two-thirds and the inferior free edge of the falx cerebri, and the tentorium cerebelli, will be seen to become stretched and tense. At the same time the septa move as a whole, which can be appreciated by observing the anterior point of junction between the falx and tentorium; this will be seen to be displaced upwards and slightly forwards, the upward movement being much more pronounced than the forward. If, now, the compression be continued, the tension increases, and finally the tentorium becomes overstretched and tears near its free border just below its junction with the falx.
The manner in which this sequence of events occurs is this. That part of the cranial vault which becomes elevated and bent gives attachment to, approximately, the middle two-thirds of the falx. This part of the falx is therefore pulled upwards by the vault ; but it is attached below to the tentorium cerebelli and is thereby prevented from accompanying the vault upwards. In consequence, the middle two-thirds of the falx becomes tense and stretched. The pull from the falx is transmitted to the tentorium, which in its turn also becomes tense and stretched.
This result is radically different from what might on first thoughts be expected to occur ; for, owing to the approximation of its posterior ( occipital bone) to its anterior (crista galli) attachment, the falx might reasonably be conceived to become slack instead of tense. The true conception of what should occur only becomes clear when it is recollected that the part of the falx attached to the elevated vault is anchored clown by the tentorium cerebelli.
Next compress the head between the vault and the base, as occurs in face and brow presentation, so that it becomes lengthened antero-posteriorly by the backward displacement of the occipital bone. The free border of the tentorium and the lower free border of the falx will be seen to become stretched and tense ; the remainder of the falx becomes slack, owing to the approximation of its attached and free borders by the lowered elevation of the vault of the cranium.
The septa should be regarded as stays to the cranial bones, like the stays of a mast. Excursion of the bones and bending are resisted by the tension of the septa, just as the swaying of a mast is resisted by the tension of its stays. If excursion and bending of the bones are too great the septa tear, just as the stays of a mast will snap if it. is forced to sway too much. Carrying the simile a stage further, the breaking of a mast’s stays allows it to over sway and break ; the tearing of the septa permits still further displacement and bending of the cranial bones which brings about dangerous disturbances in the relationship of the intracranial contents.
According to this conception the septa exert a protective function in labour ; they form a defensive system against excessive alterations in the shape of the foetal head. Moulding of the head is, up to a point, a very beneficial process, without which many a foetus could not be born ; but excessive moulding is dangerous and may cause foetal death by producing intracranial disturbances, the most evident of which is, as I shall later show, cerebral haemorrhage from the overstretching and rupture of certain blood-vessels.
Striking confirmation of the theory that the septa are designed to take stress is found in the fact that they contain special strengthening bands and fibres, arranged on admirable mechanical principles along the lines where stress is likely to fall during moulding of the head. I shall now describe these stress-bands and stress-lines in detail.
III. ON THE ANATOMY OF THE SEPTA, ESPECIALLY AS REGARDS THE STRESS-BANDS AND STRESS-LINES.
The dura mater consists of two layers, an inner and an outer, which differ widely in structure and function, and, no doubt, in origin. The outer layer is a tough fibrous membrane lining the inner surface of the cranial bones ; it is in reality their inner periosteal layer and will subsequently be referred to as the periosteal layer. This layer is the important one from the point of view of the present subject ; it sends into the cranial cavity the well-known septa, and is channelled by the large venous sinuses. The inner layer forms an inner lining to the periosteal layer and its septa ; it is a thin transparent membrane resembling a serous membrane, formed of white fibrous tissue and elastic fibres and lined by a single layer of epithelium. Its function is to serve as a smooth, slippery, elastic membrane for the brain to rest on and to impinge against with the least possible friction.
The periosteal layer projects into the cranial cavity four sheets or septa of fibrous tissue, (1) the falx cerebri, (2) the two halves of the tentorium cerebelli, (3) the falx cerebelli. These septa take origin along the course of the great venous sinuses which are themselves channels formed in the substance of the periosteal layer. The line of origin of the falx cerebri follows the course of the superior longitudinal sinus, that of the tentorium cerebelli the lateral sinus, and that of the falx cerebelli the occipital sinus. The septa meet opposite the position of the greatest sinus of all – the torcular herophili.
Two points are here of importance ; the membrane is especially strong where it forms the walls of the sinuses, and opposite the sinuses the membrane is firmly adherent to the bone, whereas elsewhere it is readily separable. Where the falx cerebri and tentorium cerebelli meet they blend together and form a strong band or line. This line may, for descriptive purposes, be termed the white line : its position may be gathered by referring to Fig. 4, where the black dotted line indicates the floor of the straight sinus, which runs backwards in a channel formed in the falx cerebri. The white line pursues a straight course for the anterior two-thirds of its length, making an angle of 45 ° with the horizontal ; for the remainder of its course it runs more horizontally, following closely the flow of the straight sinus, and ends in a thick band or mass of fibrous tissue attached to the occipital bone in the region of the torcular herophili.
These septa of the periosteal layer are not of equal strength and thickness throughout, but, at certain d e finite places, there is an aggregation of fibres which form strengthening bands.
These bands are, I believe, developed to enable the cranium and its contents to withstand the effects of excessive stress during labour.
They are certainly disposed on admirable mechanical principles in the particular parts of the septa which are most likely to have to bear the greatest strain. The tentorium and falx no doubt serve other functions than that of protecting the foetal cranium and its contents from the effects of excessive stress, but I am convince d that this protective function is of the highest importance.
According to the main directions in which they run, these strengthening bands may be roughly, but I believe usefully, divided into two main systems :
1. The antero-posterior system.
2 . The vertical system.
To illustrate their arrangement I have had two semi-diagrammatic drawings made. Fig. 3 is a foetal head, bisected in the sagittal plane, the line of section passing immediately to the left of the falx cerebri ; it illustrates the arrangement of the antero-posterior system. Fig. 4 is from a foetal head, after removal of the parietal and part of the frontal and occipital bones, so as to expose the right half of the tentorium and the falx in their entirety. ln both these drawings the chief aggregation of fibrous tissue, in strengthening bands, appears white.
Fig 3. Semi-diagrammatic drawing to show arrangement of strengthening bands of antero-posterior system. The head has been bisected sagittally immediately to the left of the Falx Cerebri. (A) points to superior longitudinal sinus ; (B) to Torcular Herophili ; (C) to occipital sinus ; (D) to main mass of fibrous tissue ; (F) to band descending from posterior end of superior longitudinal sinus ; (F) to Falx Cerebelli ; (G) to deep horizontal band ; (K) to white line ; to triangular area in anterior part of Tentorium.
Fig 4. Semi-diagrammatic drawing to show arrangement of fibres in falx ans in superficial layer of tentorium, after removal of parietal and part of occipital and frontal bones. (A) points to black dotted line indicating floor of straight sinus ; (B) points to white dotted line indicating position of deep horizontal band : (C) points to anterior vertical band.
1. The Antero-posterior System. In the region of the torcular herophili is a mass of fibrous tissue, firmly attached to the occipital bone; it is broken up, and its arrangement complicated by being channelled by the torcular and the terminations of the superior longitudinal, straight, and occipital sinuses. lt seems to have three components, (1) the central and densest part is a wedge-shaped mass, firmly adherent to the occipital bone opposite the occipital protuberance, and lying below and to one side (generally to the left) of the torcular, (2) the upper part is a strong band which at first lies free, like a pillar, in the lumen of the superior longitudinal sinus ; it passes downwards and forwards, in front of the torcular, to join the central mass ; (3) its lower part is a broader but thinner collection of fibres disposed around the occipital sinus, forming the falx cerebelli. This main mass of fibrous tissue forms the meeting point of all four septa of the dura mater : it is the sheet-anchor of the whole complicated system.
The chief continuations forwards of the main mass consist of two extremely important bands of considerable strength. These two bands are symmetrically placed on either side and originate fanwise from the sides of the main mass ; their fibres converge as they pass forwards to be inserted into the anterior clinoid processes ; they run along the lower surface of each half of the tentorium and form the straight part of its free edge. They may be termed the inferior horizontal bands of the tentorium, and play an important part in resisting excessive cranial stress. They are depicted in Figs. 3 and 5.
Fig 5. Drawing of under surface of Tentorium Cerebelli to show the origin and course of the deep horizontal bands. The head has been sawn through horizontally just below the level of the Tentorium. (A) points to deep horizontal band of right side ; (B) to posterior end of free edge of Falx Cerebri ; (C) to Torcular Herophili ; (D) to left lateral sinus ; (E) to occipital bone ; (F) to body of sphenoid.
2.The Vertical System. This system illustrates admirably the mechanical principle of stress-lines, and is represented in Fig. 4. It consists of two opposing sets of convergent fibres which meet in their points of convergence. From above downwards converge fibres from the falx cerebri ; from below upwards converge fibres from the tentorium. From the falx the fibres originate from its middle two-thirds ; from the tentorium the fibres originate chiefly from that part which covers the lateral sinus. The converging fibres meet in a strong broad band whose centre, roughly, is placed along the anterior fifth of the white line. This band may be called the vertical band of the tentorium. The main part of the band belongs to the tentorium and forms the curved part of its free edge ; as it curves downwards and forwards it blends with the horizontal band of the tentorium. This band is subjected to strain in almost every labour; it is stretched when the head is elongated vertically.
I wish to direct particular attention to the triangular part of the tentorium which is bounded above by the white line, below by the line of the horizontal band of the tentorium, and in front by the curved free edge of the tentorium. It includes the anterior vertical band of the tentorium. It is part of the tentorium most commonly subjected to strain and most commonly torn.
The tentorium cerebelli, from the above description, is seen to be strengthened by two main sets of fibres : (a) a superficial set which sweeps upwards and inwards to be inserted into the white line and the anterior vertical band, and (b) a deep set which consists of the horizontal band. lt frequently happens that when the tentorium is overstretched the tear consists in the upward separation of the anterior vertical from the horizontal band, instead of a simple tearing through of the anterior vertical band. This is illustrated in Figs. 10 and 11.
Ill. ON THE MORBID ANATOMY OF TEARS OF THE SEPTA AS FOUND IN 81 FOETUSES.
Passing now from theory to facts, do the facts, as ascertained by the circumstances in which the tears arise and the positions they occupy, in the septa of dead foetuses, support the theory ?
I think they undoubtedly do. I have pointed out that as the head changes in shape, as in moulding, tension is thrown on the septa ; that such tension occurs along definite lines of stress, strengthened by additional fibres and bands; that when the alteration in shape and consequent tension become excessive, the septa become overstretched and tear; and that the tears will naturally occur in that part of the septal system which is included within the area of stress and along the line of greatest stress.
When the tentorium cerebelli tears, the tear, as would be expected, nearly always is found in the triangular area I have described as situated beneath the line of junction of the tentorium and falx, and bounded in front by the anterior vertical band.
The tears may affect one or both sides of the tentorium, and may be complete or incomplete. Complete tears involve both the superficial and the deep layers of the tentorium ; incomplete tears involve only the superficial layer, either the vertical band or the fibres posterior to it. Complete tears usually involve the free border of the tentorium ; sometimes the free border is left intact, by reason of the extra strength it gains from the anterior vertical band, and the tear is in the nature of a perforation. In the latter case, the vertical band is always found hanging slack, which shows that it has been stretched beyond the limits of elasticity, and often contains a small haematoma. A not uncommon variety of complete tear is when the superficial layer, including the vertical band, is separated from the deep layer, including the horizontal band ; this form of tear necessarily involves a certain amount of tearing through the free border of the tentorium. Very commonly a haematoma is found in that region of the tentorium which usually tears ; this, I believe, is a sign of excessive stretching without tearing.
Ali these varieties of tears are shown in the illustrations. Fig. 6 (Case 51) shows bilateral complete tears , that on the left side being a perforation. Fig. 7 (Case 7) shows a complete tear on the right side involving the straight sinus. Fig. 8 (Case 52) shows a large perforating tear in the right side. Fig. 9 (Case 28) shows extensive bilateral tears, with rupture of the wall of the posterior end of the left lateral sinus. Figs. 10 and 11 (Case 34) show the inner and outer aspects of a tear involving separation of the anterior vertical from the deep horizontal bands (the vein of Galen was torn in this case). Fig. 1 (Case 78) shows an incomplete tear through the base of the anterior vertical band, and Fig. 12 (Case 21) shows an incomplete tear of the superficial fibres below and behind the anterior vertical band.
Fig.6 (case51) : Complete bilateral tear of the Tentorium Cerebelli. On the right side the anterior vertical band has been torn through ; on the left side the anterior border of the band has remained intact.
Fig.7 (case 7) : Complete tear of Tentorium Cerebelli, elliptical tears of Falx Cerebri. The tear is in the right side of the Tentorium. The anterior one-third of the line of junction between the Tentorium and Falx has been torn through. The straight sinus (indicated by bristle) has been opened.
Fig.8 (case 52) : Complete tear of Tentorium Cerebelli on right side. The tear is a large perforation, and involve all the superficial strengthening fibres of the Tentorium and the base of the deep horizontal band.
Fig.9 (case 28) : Complete tears of Tentorium and extensive tearing of Falx. In the Tentorium there are two perforating tears on the left side ; one is a ragged tear starting below the base of the anterior vertical band and extending outwards almost to the lateral border of the Tentorium. The other is a large outwards almost to the lateral border of the Tentorium. The other is a large perforation through the superior wall of the left lateral sinus at its termination in the Torcular Herophili.
Fig.10 (case 34) : Complete tear of Tentorium Cerebelli with separation between superficial and deep layers. The anterior vertical band is widely separated from the deep horizontal band.
Fig.11 (case 34) : Some specimen as in Fig.10. Seen from within after digital bisection of head just to left of Falx.
Fig.12 (case 21) : Incomplete tear of Tentorium Cerebelli, left side. The superficial fibres have been torn through just below base of anterior vertical band. There is also a small elliptical tear in the Falx.
A summary of the tears is as follows :
1. Bilateral, 64 : a) both complete : 35 b) both incomplete : 15 c) one complete and one incomplete : 14
2. Unilateral, 17 : a) complete : 8 b) incomplete : 9
Tearing of the falx cerebri was found, always in association with tearing of the tentorium, in only five cases (Nos. 7, 21,27, 43, and 59). The tears, one or more in number, lay in middle two-thirds of the falx, and were elliptical in shape, with the long axis of the ellipse lying, as would be expected, in the line of stress.
IV. ON THE MODE OF ORIGIN AND SOURCE OF SUBDURAL CEREBRAL HAEMORRHAGE.
Subdural cerebral haemorrhage, varying in amount from a few drops to a copious haemorrhage, was found in all but six cases (Nos.21,33,41,48,50,73). The haemorrhage may be classed as severe, moderate, or slight. Severe haemorrhage accompanies a higher proportion of bilateral complete than of other varieties of tear, but there is no constant relation between the extent of the tear and the amount of haemorrhage, as the following table shows :
The haemorrhage does not originate from the tear itself; the fact that in six cases there was no haemorrhage whatever, and that, in a few other cases, the tear itself, occupied by a tiny clot, lay entirely outside the boundaries of a fair-sized subdural haemorrhage, is good proof of this. The tentorium cerebelli contains only a few fine capillary vessels (excepting, of course, the lateral sinus).
It was seldom possible, except in the few cases where a large sinus or blood-vessel had ruptured, to find the exact source of the haemorrhage ; the lesser cerebral vessels are so small and delicate, and the fine arachnoid connective tissue surrounding them becomes so infiltrated with blood, that it is impossible to isolate them with accuracy from the surrounding haemorrhage. In Case 28 the lateral sinus, in Case 7 the straight sinus, and in Case 34 the vein of Galen were found ruptured ; in these cases the haemorrhage was enormous, and its source obvious. Failing the detection of the ruptured vessel, a valuable clue to the origin of the haemorrhage is its exact situation in the subdural space and its relation to surrounding structures, especially blood-vessels. In order to determine this more accurately I made small openings in some of the heads in which I expected to find haemorrhage and soaked them in formalin solution for a month before dissection. A large haemorrhage is not helpful for this purpose as its spread is too diffuse, but a small haemorrhage is necessarily confined to a small area of the subdural space. lt soon became apparent that the origin of the haemorrhage could be pinned clown within narrow limits ; for it was found that, in cases of cerebral haemorrhage, a certain situation in the subdural space was never free from blood, and that, in the case of small haemorrhages, the blood was always confined to this one situation and was in relation to the same blood-vessels. This situation is a narrow area bounded in front by the transverse fissure, behind by the upper part of the tentorium, below by the pons varolii, and laterally by the mesial aspects of the anterior lobes of the cerebellum ; its centre corresponds to the course of the great vein of Galen. The blood-vessels which occupy this area are the vein of Galen and its tributaries. As these vessels are precisely the ones that are likely to be stretched and torn, and as in two cases I found the great vein of Galen itself ruptured, it is reasonable to draw the general conclusion that these vessels are the origin of the haemorrhage in cases of excessive cranial stress.
The mechanism which leads to stretching and tearing of these veins must now be considered. Any movement of the apex of the tentorium is necessarily transmitted to the vein of Galen, whose fixed point is at its entrance into the straight sinus. In the common forms of cranial stress, i.e. , anteroposterior longitudinal stress, it has already been pointed out that the apex of the tentorium is drawn upwards, and that this upward displacement is very considerable in cases of excessive stress. The vein of Galen follows this movement with two results : (1) its line of direction is altered, and (2) it becomes stretched and tense. The altered course of the vein is admirably shown in Fig.1 ; instead of passing backwards and slightly upwards, the vein is seen to be running almost directly upwards and making an acute angle with the straight sinus. In consequence, the vein becomes kinked at its entrance into the sinus, with the result that the flow of blood is impeded or obstructed. The enormous distension and engorgement of the vein of Galen and its tributaries is always a striking appearance in cases of torn tentorium, and, together with the anatomical findings, is sufficient evidence of the occurrence of the series of events I have described. If, now, the distended veins are still further stretched, they rupture; it is sufficiently obvious that a vein whose walls are already in a state of high tension from engorgement will more easily rupture, as the result of further longitudinal stretching, than a vein whose walls are in a normal state of tension.
It now remains to consider which particular veins are ruptured. The vein of Galen itself is seldom ruptured : the rupture of such a prominent vessel could seldom escape careful observation, and I was only able to detect it twice. In these cases the vein had yielded at its fixed point, i.e, at its point of entrance into the straight sinus. The tributaries which the vein of Galen receives, from the point of its formation by the junction of the two internal cerebral veins to its termination in the straight sinus, are (a) the two basal veins, (b) veins from the superior surface of the cerebellum, which run forwards and upwards to join the vein of Galen, (c) veins from the mid-brain, and (d) veins from the Pons. Another set of veins, although they do not enter the vein of Galen, must also be considered : these are veins passing from the superior surface of the cerebellum directly into the straight sinus. With the exception of the basal veins, the above veins are too small and delicate to be satisfactorily traced in the foetus, unless they are distended with blood. I believe, so far as my observations go, that the usual source of haemorrhage in these cases is from the tributaries which the vein of Galen receives from the cerebellum and mid-brain, and from the cerebellar veins which enter the straight sinus.
The mechanism of stretching and rupture of these veins is as follows. They are stretched between their two fixed points ; their upper fixed point is the vein of Galen, and their lower is the cerebellum. The vein of Galen, as already described, is displaced upwards and forwards, and is kinked, by the pull of the tentorium ; the cerebellum is not only held clown, but is pressed still further clown into the posterior fossa, by the downward pressure of the posterior poles of the cerebral hemispheres. In consequence of the upward pull and kinking of the vein of Galen, and the fixation or downward pull of the cerebellum, these delicate veins become stretched and engorged, and finally ruptured. The same mechanism of rupture applies to the cerebellar veins which enter the straight sinus direct.
V. CLINICAL PART : ANALYSIS OF THE EIGHTY-ONE CASES.
In macerated foetuses the dura mater is so softened and weakened and the loosened cranial bones allow of such extreme alteration in the shape of the head, that tears of the tentorium and falx are seldom absent.
For purposes of clinical analysis the 81 cases found in the 168 fresh foetuses may be divided into two main groups :
1. Those in which the foetus was delivered by the head, 46 cases.
2. Those in which the foetus was delivered by the breech, 35 cases.
The 46 head-first deliveries comprised 44 cases of vertex presentation ; one case of face presentation in which labour ended naturally (No. 28), and one case of brow presentation, in which labour was ended by forceps (No. 75).
Analysing further the 44 cases of vertex presentation, it will be seen that 25 were cases of forceps delivery and that the other 19 were cases of natural delivery.
(I) Forceps Cases.
The indications for the use of forceps were as follows :
(a) Contracted pelvis, 7 cases. The low operation was used in 4 cases (No. 18 after pubiotomy), and the high in 3 (No. 30 was followed by Caesarean section).
(b) Placenta praevia, 4 cases. The low operation was used three times and the high once.
(c) Prolapsed cord, 4 cases. The low operation was used three times and the high once.
(d) Prolonged second stage of labour. In six the delay was due to persistent occipito-posterior presentation ; in one of these the foetus was extremely large (No. 80). In four it was said to be due to uterine inertia.
In considering these forceps cases, it is apparent that in some the cranial stress must have been excessive ; such are all the cases of high forceps operation (always accompanied by a high foetal death-rate), of pelvic contraction, of prolapsed cord, and those cases of placenta praevia in which the foetus was delivered rapidly. In such cases tearing of the tentorium is readily accounted for.
On the other hand, in cases where forceps is applied merely for a prolonged second stage due to malposition of the head or inertia of the uterus, the occurrence of the tearing of the tentorium invites criticism. The production of sufficient cranial stress to make the tentorium cerebelli tear means either that the force exerted by the forceps was excessive or was applied to the wrong diameter of the head, or both ; neither should occur if the os is fully dilated or if the occiput is directed forwards. If forceps is responsible for the saving of many foetuses, it is also responsible for the unnecessary death or injury of others ; it is used too often and on the flimsiest indications.
As regards the direction of the applied force, the most dangerous direction is when the forceps is applied to the anteroposterior diameter of the head, or to one approximating it. Even a moderate amount of force applied in this direction can, by causing vertical elongation of the head, lead to stretching and tearing of the tentorium. The risk of applying forceps to the extremely plastic head of a premature foetus is well known.
(2) Natural Delivery in Vertex Presentation.
In some of these cases the conditions were favourable for the occurrence of excessive cranial stress ; in others it is puzzling to find the reason. The 19 cases may be analysed as follows :
Normal vertex presentations, 3 cases (Nos. 64, 71, 79).
Twins (one foetus lived in each case), 3 cases (Nos. 13,23, 53).
Placenta praevia, 3 cases (Nos 50, 57, 61).
Accidental haemorrhage, 4 cases (Nos. 22, 39, 48, 68).
Long second stage (occ. ant.), 1 case (No. 45).
Rapid labour following induction for albuminuria of pregnancy, 1 case (No. 70).
Precipitate labour, 1 case (No. 65) .
After former colpoperineorrhaphy, 1 case (No. 19) .
General oedema of foetus , l case (No. 27).
Persistent occipito-posterior, 1 case (No. 74).
Two were cases of normal full-time labour (Nos. 71 and 79), i.e., the second stage was not too rapid or too long, the resistances were not unduly great, the occiput was forwards, and the foetus was neither premature nor of great size. In others, prematurity of the foetus, with the consequent greater plasticity of the cranium, is the only predisposing factor to be found; such are one of the cases of normal labour (No.64), the cases of twins in No. 13 the head was born with the occiput behind – two of the cases of placenta praevia (Nos.50 and 61), and three of the cases of accidental haemorrhage (Nos. 39, 48, and 68). A very rapid second stage, unless the resistances be slight, and especially if the foetus be premature, is an easily appreciated factor ; such are cases 19, 65, and 70. It is to be noted that pituitrin was given to one of the cases of placenta praevia (No. 50, foetus premature), and to one of accidental haemorrhage (No. 22) ; the action of this powerful ecbolic as a possible factor in producing excessive cranial stress should not be overlooked. Case 19 is an admirable example of a combination of many factors ; the mother had an extensive colpoperineorrhaphy done a year previously for prolapse of the uterus, and the premature foetus (syphilitic) was expelled with great rapidity, causing severe laceration of the thick, resistant perineum.
It is not at all easy to give a reasonable explanation for the torn tentorium in many of these cases of natural vertex delivery. I strongly suspect that over-zealous « guarding » of the perineum from rupture, especially by strong forward pressure against the perineum forcing the occiput against the symphysis, may explain some.
Tears of the tentorium cerebelli are found with great frequency in dead foetuses delivered by the breech. There are 47 cases of breech delivery amongst the 168 fresh foetuses, and I have found tearing of the tentorium in 35, or, approximately, 75 per cent.
The explanation is simple, and I have already referred to it. During its final passage the after-coming head is rapidly, though comparatively momentarily, compressed in a series of diameters lying between the forehead and the occiput ; compression in this direction causes vertical elongation of the head (see Fig. 2, II.), and I have already pointed out that it is this particular alteration in shape which throws the greatest strain on the tentorium cerebelli.
Analysis of Cases.
Cases of breech labour present a wide divergence in type. In order to appreciate the significance of tears of the tentorium in breech delivery it is necessary to classify the cases. Where the after-corning head is dragged through a contracted pelvis, or where the foetus has had to be delivered rapidly for such complications as antepartum haemorrhage, the discovery of the effects of excessive cranial stress might reasonably be anticipated. But tearing of the tentorium is by no means confined to cases of this type. It is a significant fact, and one of great practical importance, that many are cases of what may be called ordinary, normal breech labour.
Breech labour may be divided into three classes :
(1) Primary uncomplicated breech presentation, in which there are no complications of pregnancy, and no complications of labour ( except premature labour) other than those arising direct from the presentation, such as extended legs or arms, prolapse of the cord.
(2) Primary complicated breech presentation, such as breech presentation in cases of antepartum haemorrhage, contracted pelvis, etc.
(3) Breech by version.
The 47 cases of breech delivery, and the 35 with tearing of the tentorium cerebelli, are distributed amongst these classes as follows :
(1) Primary uncomplicated breech. Total number of cases, 17 ; tearing of the tentorium found in 15.
(2) Primary complicated breech, total number of cases, 2 ; tearing of the tentorium found in neither.
(3) Breech by version, total number of cases, 28 ; tearing of the tentorium found in 20. In these 20, the version was performed for the following complications :
Placenta praevia : 10 cases.
Transverse presentation : 5 cases.
(Including a case of spontaneous evolution.)
Contracted pelvis : 3 cases.
Brow presentation : 2 cases.
A broad survey of these figures reveals facts which, to myself at all events, are novel and significant.
(1) Tearing of the tentorium is found in 75 per cent. of dead foetuses delivered by the breech when all classes of breech delivery are included.
(2) Tearing of the tentorium is found in 88 per cent. of dead foetuses in case s of primary uncomplicated breech presentation, i.e., as the result of normal breech labour. In none of these cases was there any reason for undue resistance to the passage of the head, from contraction of the maternal passages or from excessive size or malposition of the foetal head. Nor was there any apparent reason for rapid delivery of the foetus. lt must be admitted that tearing was favoured by prematurity of the foetus (for this purpose I include foetuses below 48 cm. long) in five cases (Nos. 2, I 5, 24, 29, and 46).
(3) Tearing of the tentorium is found in 71 per cent. of dead foetuses delivered after podalic version. This is not so surprising ; rapid delivery was no doubt practised in some of the cases of placenta praevia and in those of the transverse presentation complicated by prolapse of the cord, and in the cases of contracted pelvis there was great resistance to the passage of the head. But the significance of these findings is this : it is more than likely that some of these foetuses escaped death from the primary complication only to meet it as the result of breech delivery. In any case it is a pity to kill a foetus twice. It is true that in many of these cases the version was performed for the sake of the mother, whose interests must always be paramount ; but if a breech delivery be properly managed there should never be sufficient cranial stress to lead to tearing of the tentorium-excluding, of course, cases where rapid delivery is indicated.
On the Actual Causation of Foetal Death in Cases of Excessive Cranial Stress. In this condition, as indeed in most others, it is impossible to assign the exact cause of death. Quite apart from the two great visible effects of tearing and haemorrhage, we have to consider the general rise of intracranial pressure, the evidence of which is not seen post-mortem. What part this plays in causing death must be left to the imagination; perhaps the crowding clown of the medulla oblongata into the foramen magnum results in dangerous pressure on the so-called vital centres. In cases where there is a large, or moderate, haemorrhage, it is fair to assume that the foetus has been killed by the haemorrhage. But even this does not always kill the foetus, for I have performed post-mortems on several infants, who have survived birth by as much as two days, who displayed extensive bilateral tears of the tentorium and large haemorrhages ; such infants had, of course, been in a precarious condition since birth. The position of the haemorrhage is probably of importance; a small haemorrhage confined beneath the tentorium would be more dangerous than a larger and more diffuse one above this region. The actual tears, unaccompanied by haemorrhage, cannot be regarded as fatal injuries ; the septa of the dura mater are not vital structures, nor are they the source of haemorrhage. Furthermore, evidence of tearing of the tentorium may be found in infants who have survived birth for a long time. Having survived the original stress, there is no reason why a child should be much the worse for a torn tentorium, provided there has been no, or only very slight, haemorrhage. It cannot yet be stated what precisely are the effects in after-life of these injuries ; there is no collected evidence. I feel sure that if pathologists who are in the habit of performing post-mortems on children were to look for evidence of these tears, they would find it surprisingly often. I have personally found one such example in a child of six months old, in whom there was a large complete tear, with healed edges, in the left side of the tentorium. There is, unfortunately, no clinical record of this case, as the child died shortly after admission into hospital, before notes could be made. A point of great interest is the oblique shape of the head which had persisted since birth; the permanent alteration in the shape of the head, in combination with a torn tentorium, is of great importance in throwing light on the aetiology of the rare infantile condition known as « oblique head. » It also tends to support my theory that the septa of the dura mater act as supports or stays to the bones.