The Surgery of the Skull and Brain

by Louis Bathe Rawling

FRACTURES OF THE BASE OF THE SKULL

Fractures of the base of the skull are produced in two ways:—

1. By violence applied directly to the base—perforating wounds of the orbit, bullet-wounds through the mouth and base of skull, the driving inwards of the bones of the face, the driving upwards of the condyle of the jaw (the ‘knock-out’ blow of the pugilist), and, as the result of heavy falls on to the feet or buttocks, the upward driving of the condyles of the occipital bone.

2. By violence applied indirectly—blows applied directly to the vault and transmitted to the base. This variety will be considered first as it receives the greatest prominence in surgical textbooks. Various explanatory theories have been advanced, of which the following are the more important:—

(a) Aran’s theory of irradiation.

This theory states that ‘fractures of the base result as extensions from fractures of the vault, the fracture following the shortest anatomical route to the base’. Although this theory must be accepted as offering a satisfactory explanation for the occurrence of a certain proportion of basic fractures, such, for instance, as result from a blow applied directly to the vertex, it certainly cannot be accepted as accounting for the great majority of basic fractures. The theory was advanced on the hypothesis that basic and vault fractures were necessarily co-existent. That combined lesions of this nature are frequently in evidence is not to be doubted for one instant. It is, however, ‘putting the cart before the horse’ to say that the vault fracture is always the primary lesion. Such is by no means the case.

(b) The bursting and compression theories.

The skull is here regarded as an highly elastic sphere, compression of which leads to diminution in the diameter along the axis of greatest pressure, bulging occurring in other diameters. The bulging exceeding the limits of elasticity a fracture occurs, the line of fracture varying according to the different features present. Thus, when the lines of fracture run parallel to the direction of the compressing force the bone bursts open along the convexity (bursting fractures), and when the lines of fracture run at right angles to the direction of the compressing force a fracture by compression is said to result (compression fractures).

These theories are based on experiments carried out on the cadaver, the skull being enclosed in a tight-fitting box and subjected to pressure sufficing to bring about a fracture. Undoubtedly, the head may be compressed between two forces, as, for instance, when a person is knocked down in the street, the vehicle passing over the head, or, as in a case recently under my care, where a boy, hanging by his feet from the side of a barge, was crushed between the barge and the wharf as the vessel swung inwards with the tide. Cases of bilateral compression are, however, of infrequent occurrence, the great majority of basic fractures resulting from blows applied directly at the region of the level of the base of the skull (see [p. 76]), or from the forward propulsion of the body, the head coming into violent contact with a resisting object, as, for instance, when a person is thrown out from a motor-car, the head striking against a tree, brick wall, &c. In the first case, there can be no question of bilateral compression, and in the second the compression is exerted between the vertex and the occipital condyloid region.

Moreover, the fundamental points on which the bursting and compression theories are grounded are based on erroneous principles. The skull cannot in any sense be regarded as a sphere, nor does it possess the requisite elasticity to bulge and allow of compression in the manner that the theory demands. The skull, in reality, forms rather less than two-thirds of a sphere, the base passing inwards from the lower limits of this partial sphere in a more or less horizontal plane. This can be readily verified by placing the skull on a table so that its base corresponds to the surface of the table. The elastic properties of the skull have also been greatly exaggerated, and far too little attention has been paid to the peculiar anatomical formation of the base.

(c) The contre-coup theories.

Fractures of the base occasionally occur in which evidence is conclusive that the blow was received on the vault, the vault itself remaining uninjured. Such cases have given origin to this theory, one stating that ‘from the point struck a wave is transmitted through the semi-fluid brain, producing a fracture at some more distant point’. Helferich, for instance, maintains that isolated fractures of the orbital roof, and more rarely of other parts of the base, are produced by the influence of hydrostatic pressure. There can be no question that waves are transmitted through the brain and cerebro-spinal fluid, but that such waves should be capable of producing a basic fracture is, in my opinion, beyond the bounds of possibility. The theory is opposed to all my experience of basic fractures, and the cases brought forward in support are capable of a much more probable explanation. The base is undoubtedly the weakest part of the skull, and a blow on the vault may fail to produce a local lesion and yet, when the force is transmitted to the weaker base, may there bring about a more definite result. For instance, it is by no means uncommon to find that a blow on the frontal region fails to fracture the vertical plate of that bone and yet suffices to produce a fracture, often comminuted, of the orbital plate of the frontal bone or of the cribriform plate of the ethmoid, two fragile plates, either of which may shatter like a plate of glass from the effect of forces transmitted across them. In further support of this theory, the following case, recently under my care, may be cited. The patient received a heavy blow over the left occipital region. A fracture passed inwards across the left cerebellar fossa towards the posterior border of the foramen magnum, and a second fracture, entirely distinct from the first, passed across the right orbital plate of the frontal bone. In this case, the force conducted across the base, from behind forwards, failed to fracture the strong basi-occiput, but succeeded in producing a more definite lesion on reaching the fragile orbital plate.

Some of the celebrated surgeons of the last century insisted that the course pursued by basic fractures was to be explained on anatomical grounds, but their views have been neglected and theories based on experimental evidence have been accepted in their place. All experiments, such as those previously mentioned, are useless, and definite conclusions can only be gained by carrying out in every case the following method of investigation: (1) by obtaining in the first case an accurate history as to the manner in which the injury was received; (2) by noting all visible and palpable signs of external injury; (3) by careful observation of all the clinical symptoms during the progress of the case; (4) by comparison of such with the lesions found in case of death.

Over 300 cases have been investigated by me after these principles. In about 30 per cent. of the cases sufficient evidence was obtained to show that the basic fracture resulted and extended from a primary fracture of the vault. These cases were to be explained by Aran’s theory of irradiation. This theory, however, errs in stating further that the fracture follows the shortest anatomical route to the base. This is not correct, for the line of fracture corresponds to the direction of the applied force and is influenced to a very large extent by the resistance offered, the weaker areas being picked out and the strong buttresses avoided. It is only in the most severe cases that the fracture travels to and traverses across the base in such a direction as to show that, for the time being, all laws are in abeyance.

In about 5 per cent. of cases the fracture resulted from bilateral compression, from falls on to the buttocks, &c., and from blows applied to the angle of the jaw. These cases afforded examples of the bursting and compression theories.

On the other hand, in over 60 per cent. of cases, the injury was received over one of the following situations: (1) in front, over the frontal eminence or supra-orbital ridges; (2) in the antero-lateral region, over the external angular frontal process; (3) in the lateral region, over the lower temporal, auricular, and mastoid regions; (4) in the posterior region, over the superior curved line of the occipital bone or over the external occipital protuberance.

In all these cases, therefore, the blow was inflicted at or near the level of the base of the skull, the resultant fracture being a fracture by direct violence, the fracture traversing the base and splitting it much in the same way as a chisel splits a board of wood. The ‘grain’ of the wood may be regarded as representing the weaker basic lines, and any ‘knot’ the resistance offered by the strong basic buttresses, the forces being momentarily turned aside, but soon again passing onwards, parallel to the original direction, but not necessarily in the same straight line.

Fig. 30. Plan of the Base of the Skull. a, a, The transverse pre-condyloid line; a′, a′, The line pursued, in whole or in part, by the ‘typical’ basic fracture.

Any blow delivered at or near the basic level tends primarily to involve the weaker area, the base, passing secondarily upwards on to the vault. One may go even so far as to say that in most combined vault and basic fractures, the vault fracture is a secondary development, the basic fracture being the primary lesion.

There is, however, still another important anatomical feature bearing on the mechanism of basic fractures, one that must necessarily come into force in the greater number of such fractures. The base of the skull may be said to consist of two parts, one lying anterior to the condyles of the occipital bone, the other posterior to and including the condyles with their vertebral attachment. These two segments are united to one another by a weak chain—represented by a line drawn from one external auditory meatus to the other, with, as a connecting link, the sphenoidal sinus in the middle line.

When the base of the skull is viewed from below, it will be seen that the weak line includes both Glaserian fissures, both petro-sphenoidal sutures, both foramina lacera media, with the sphenoidal sinus again as a connecting link. The two parts of the skull are, to all intents and purposes, merely cemented together by the union of the basi-sphenoid and basi-occiput. Consequently, if a blow be received on the antero-lateral region of the head, the anterior segment tends to be split off from the more fixed posterior part, the fracture following the weak line previously indicated. This weak line occupies so important a position in the mechanism of basic fractures that careful observation will show that the greater number of middle fossa fractures follow that line, wholly or in part. Such a fracture of the middle fossa may be termed ‘the typical fracture of the base of the skull’ (see [Figs. 30], [34] and [39]).

Summary of theories.

Aran’s theory of irradiation, with certain modifications, accounts satisfactorily for about 30 per cent. of basic fractures.

The contre-coup theory may be rejected entirely.

The bursting and compression theories are unsatisfactory, accounting for not more than about 5 per cent. of fractures.

The majority of cases result from direct violence applied at or near the basic level, the fracture passing across the base in the general direction of the applied force, but not necessarily in the same straight line.

Up to this point certain facts and theories have been discussed, such as bear on the general mechanism of basic fractures. It now remains to consider other factors that exercise influence on the general direction of the fracture.

The influence of sutures on the line of the fracture.

Complete maceration of the skull is always essential in endeavouring to estimate in what way the various sutures of the skull influence the extent and direction of a fracture. Sutural separation is generally regarded as of infrequent occurrence. An examination of a large number of macerated skulls has shown, however, that sutural separation is in reality of common occurrence. Certain sutures show a special liability to such changes, especially the masto-occipital, the petro-occipital, and the petro-sphenoidal. Separation of the sutures is more common in the young adult; in the infant and in the old such conditions are seldom observed.

Allusion has already been made to the fact that forces transmitted from the vault to the base, or vice versa, undergo a marked diminution in intensity when the sutures of the skull are encountered, the ‘fracture’ showing a marked disposition to follow the line of the suture. When the force is excessive, all rules are temporarily in abeyance, but, under ordinary circumstances, the separation along the line of a suture corresponds fairly accurately with the dentations and serrations of the suture involved. Sutural separation without actual fracture is a possible occurrence, but is decidedly rare. Such isolated fractures are confined, more or less, to the sagittal suture in the vault, and the masto- and petro-occipital sutures in the base.

The influence of air-sinuses, &c., on the line of the fracture.

The sphenoidal sinuses, two in number, are usually separated from one another by a thin septum. This septum is, however, often deficient, and a single cavity exists. The sinuses make their appearance about the seventh or eighth year; they vary greatly in size but, when fully developed, occupy the greater part of the so-called body of the sphenoid, extending backwards almost as far as the junction of the basi-sphenoid and basi-occiput, and spreading outwards into the wings of the sphenoid and over the roof of the orbit.

The sinus is bounded on all sides by a thin lamella of bone; its roof forms part of the middle fossa of the skull, the sides are separated by a thin bony wall from the cavernous venous sinus, and the floor aids in the formation of the roof of the naso-pharynx. There exists, therefore, in the very centre of the base of the skull—in the region of the so-called buttress of connexion between the posterior and anterior segments of the skull—an exceedingly weak area, one which must be implicated in the great majority of basic fractures. The ‘weak line’ of the base of the skull—previously referred to—is now still more accentuated.

The sphenoidal sinus is involved in at least 40-50 per cent. of basic fractures, comminution of the sinus wall being often so excessive that a probe can be passed with the greatest ease from the middle fossa into the naso-pharynx. Blood is thus allowed to escape readily into the naso-pharynx, and a source is opened up for the possible development of meningeal infection.

Reference to the various illustrations of fractures of the base will supply further evidence as to the special liability of the sinus region to injury. It will be seen that nearly all fractures that pass one middle fossa to the other, or from one middle fossa to the opposite anterior fossa, traverse this region.

The frontal sinuses, also two in number, are separated from one another by a thin osseous septum. Up to the age of puberty these sinuses are either absent or represented by a small cell. Subsequently, they develop rapidly, often extending into the orbital roof. The upper and inner boundary—usually very fragile—assists in the formation of the anterior fossa of the skull. The outer boundary—the perpendicular plate of the frontal bone—is much more dense, and, consequently, a fracture of the outer wall is almost necessarily associated with a fracture involving the inner or orbital boundary, that is to say with a fracture of the anterior fossa.

The ethmoid cells.

The ethmoid bone consists of a collection of cells which communicate with the nasal cavity (middle and superior meati), and which are merely separated from the anterior fossa of the skull by the thin cribriform plate. This plate of bone is of so fragile a nature that splintering occurs in the great majority of anterior fossa fractures. The special dangers that arise from the possibility of meningeal infection are obvious.

The auditory region.

That part of the petrous bone which encloses the auditory apparatus, and which transmits the seventh and eighth pair of nerves, is proportionately weakened and correspondingly liable to fracture. The special details of these fractures are dealt with on [p. 102].

Fig. 31. To illustrate the relation of Basic Fractures to Cranial Nerves.

The influence of basic foramina.

It has often been stated that a basic fracture is arrested on meeting one of the larger foramina of the skull. With this view I am not in agreement, for not only are the larger foramina frequently involved, such as the foramen lacerum posterium and medium, but the largest foramen of all, the foramen magnum, is often implicated. It will be granted that certain foramina are but rarely involved, but this is due to the fact that they are aside of the chosen and definite paths of basic fracture. Thus, the foramen ovale and the foramen spinosum are only exceptionally involved because they lie immediately anterior to the petro-sphenoidal suture, whilst the anterior condyloid foramen—transmitting the hypoglossal nerve—is rarely implicated because it lies internal to the usual posterior fossa fracture. On the other hand, the foramen lacerum medium is involved in nearly every fracture that passes from one middle fossa to the other.

The probable line of basic fracture in any given case.

When the various weaker lines and areas are taken into consideration, and when the direction and site of the applied force are known, one is generally enabled to foretell with considerable accuracy the probable transbasic course of the fracture. After investigating over 300 cases, I was enabled to frame the following rules with respect to the probable line of transbasic fracture.

Direction, &c., of the applied force.	Probable resultant basic fracture.
1. Force applied to the median frontal region.	The fracture passes backwards from the perpendicular plate of the frontal bone to the cribriform plate of theethmoid, thence between the optic foramina to the body of the sphenoid, the thin sinus roof being usually comminuted. From there thefracture diverges to the opposite side, and tearing off the posterior clinoid process, passes along the petro-occipital suture to thejugular foramen, being then continued on the other side of that foramen along the masto-occipital suture, and so again to the vault.
Fig. 32. Diagram of Lines pursued by Basic Fractures. Force appliedto the median frontal region.
2. Force applied to the lateral frontal region, in the situation of the external angular frontal process.	The fracture passes across the anterior fossa towards the sphenoidal fissure, tearing away the anterior clinoidprocess, and again comminutes the roof of the sphenoidal sinus. Progressing onwards, with or without fracturing the posterior clinoidprocess, the fracture passes either along the anterior part of the petrous bone at its junction with the greater wing of the sphenoidtowards the opposite middle and external ears, or along the petro-occipital suture to the jugular foramen, and continued along themasto-occipital suture as in the previous case.
Fig. 33. Diagram of Lines pursued by Basic Fractures. Force appliedto the lateral frontal region in the situation of the external angular frontal process.
3. Force applied to the region of the external ear.	The fracture passes across the roof of the bony auditory meatus towards the junction of the anterior and inner wallsof the middle ear, the membrane undergoing a variable amount of destruction and displacement. The fracture is then continued across thetegmen tympani, and after following the petro-sphenoidal suture reaches the foramen lacerum medium, being again continued on the oppositeside of that foramen to the sphenoidal body. Thence it pursues one of two courses. Most commonly the fracture passes backwards obliquelyto the opposite middle and external ears, following a course similar to that already indicated.
	In such cases the fracture may extend on each side up on to the vault in such a manner that the two segments aremerely united by the soft parts; whether the fracture be so complete or not, a more minute examination of the line of separation willevidence many interesting points. An inspection of the anterior aspect of the posterior fragment shows that the fracture passes just infront of the geniculate ganglion of the facial nerve, the ganglion being laid bare, whilst its petrosal branches are usually torn. Thefracture also passes anterior to the Eustachian tube and the horizontal part of the internal carotid artery. On examining this posteriorfragment the following structures will be seen, passing from without inwards: the posterior half of the external auditory meatus, themastoid antrum, the lacerated membrane and the ossicles of the middle ear, the geniculate ganglion of the facial nerve, the Eustachiantube, the horizontal part of the internal carotid artery, the Gasserian ganglion, and the posterior half of the sphenoidal sinus in themiddle line (see also [Fig. 39]).
	After reaching the sphenoidal body, the alternative course for the fracture to pursue is to pass towards the oppositesphenoidal fissure and, tearing off the anterior clinoid process, to be directed across the anterior fossa, parallel to the originaldirection but not in the same straight line.
Fig. 34. Diagram of Lines pursued by Basic Fractures. Force appliedto the region of the external ear. a ... a, The ‘typical’ basicfracture (see also [Fig. 30]).
4. Force applied to the mastoid region.	The fracture follows the occipito-mastoid suture to the jugular foramen, and is again continued on the opposite sideof that foramen along the petro-occipital suture towards the apex of the petrous bone. It then passes across the sphenoidal body to thesphenoidal fissure of the opposite side, and so across the anterior fossa. It is especially common in this particular variety of fractureto find fissures diverging from the region of the sphenoidal sinus forwards towards the cribriform plate of the ethmoid, these fissuresusually passing between the optic foramina.
	This fracture is also peculiar in so much that, when the degree of separation along the occipito-mastoid suture isexcessive, there is special liability to a tearing of the lateral sinus wall as the sinus begins to turn downwards and inwards.
Fig. 35. Diagram of Lines pursued by Basic Fractures. Force appliedto the mastoid region.
5. Force applied to the lateral occipital region.	The fracture passes across the thin cerebellar fossa and strikes the foramen magnum immediately behind the condyle.Starting again from a similar point on the opposite side of the foramen, the fracture passes outwards to the jugular foramen. Again, twocourses are now available, the fracture either cutting outwards across the body of the petrous, ‘external’ to the internalauditory meatus and cutting across the facial nerve in the region of the geniculate ganglion, and finally terminating in the roof of themiddle ear, or else passing along the petro-occipital suture and so to the foramen lacerum medium, the sphenoidal fissure, and theanterior fossa as in the previous case.
Fig. 36. Diagram of Lines pursued by Basic Fractures. Force appliedto the lateral occipital region.
6. Force applied to the posterior occipital region.	The resultant fracture varies according to the direction of the applied force. A force which is applied to theposterior occipital region at right angles to the transverse axis of the skull results in a fracture which, on reaching the posteriormargin of the foramen magnum, is continued again on the opposite side of the foramen along the dorsum ephipii. When the force is moreoblique in direction (as is usually the case) the fracture traverses the thin cerebellar fossa to the outer margin of the jugular foramen,and then follows one of the two courses indicated in the previous case.
	More commonly the fracture cuts across the petrous bone.
Fig. 37. Diagram of Lines pursued by BasicFractures. Force applied to the posterior occipital region, the fracture followingthe course a. a. or b. b., according tothe direction of the applied force.

Summary.

Basic fractures tend to follow certain definite paths, this transbasic course varying according to the direction of the force applied and the site of application of the same. Whether the fracture completely traverses the base depends on the character of the force and the resistance offered, for bases, as well as vaults, vary greatly in strength. To every rule there must be exceptions, and cases are at hand in which the fracture appears to have obeyed no law, or in which the force applied was of so forcible a nature that the fracture traversed the base, regardless of all the ordinary rules.

The principles enumerated above were formulated by me some four years ago, and, in spite of certain adverse criticisms, I am more than ever convinced that the rules are correct, and that time and research are alone required to add to the strength of my assertions.