The Surgery of the Skull and Brain

by Louis Bathe Rawling

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.