CHAPTER XXXI. FRACTURES OF THE SKULL. The skull is the bony protection of the brain and when this protective wall is injured the brain is likely to suffer, at least indirectly. <Callout type="important" title="Important">The proper treatment will usually depend on the proper diagnosis, and a proper diagnosis often calls for the most careful observation and consideration of every symptom present.</Callout> Fracture of the skull may be divided into three groups : 1. Those in which recovery would take place without treatment. 2. Immediately fatal cases, and those who live but a few hours (all treatment being futile). 3. Those whose lives can be saved or in whom serious sequelae may be averted by proper treatment. The last group is the one to which our attention is directed. It is however no simple matter to determine at the time of examination to which group a given case may belong. <Callout type="risk" title="Risk">The unexpected is more common in head injuries than in other fields of surgery; an apparently slight injury may result in death while a case presenting grave symptoms may recover.</Callout> Classification. — Fractures of the skull have been variously classified and the terms used indicate the conditions without further definition. We have fracture of the vault, fracture of the base and fractures involving both vault and base. Fractures of the base may be classified according to the fossa involved. There are fissured fractures, depressed fractures, comminuted fractures, etc., the same terms being used as are applied to fractures in general. Surgical Anatomy. — A knowledge of the anatomy of the skull and brain is essential to the proper interpretation of symptoms and the administration of treatment, but the subject is so extensive that it will be possible to consider briefly only the most salient features ; the reader being referred to text-books on anatomy for more detailed accounts. Bones of the Skull. — Development. — The bones of the vault (tabular portion of the occipital, parietals, squamo-zygomatic portions of the temporals, and the frontal) are ossified in membrane from centers which appear at about the end of the second foetal month. Ossification beginning in the center of a quadrilateral bone reaches the corners last and accordingly at birth we find the 'fontanelles' which represent the unossified portions of the bones of the vault. These fontanelles are situated at the four angles of the two parietal bones and are therefore six in number. The four lateral fontanelles at the lower angles of the parietal bones are closed a short time after birth ; the one situated at the juncti- on of the sagittal and lambdoid sutures closes within the first few months of life ; the one remaining, situated at the bregma, continues open during the first year. Although the process of ossification begins earlier in the vault of the skull than in the base, nevertheless, at birth, the base is far more completely ossified than the vault. The base is ossified in cartilage as is the rest of the skeleton. Wormian bones occur most frequently in the course of the lambdoid suture but are not uncommonly found in the fontanelles: the suture surrounding them may at first sight be mistaken for a linear fracture while exploring wounds of the scalp. In the aged the frontal, parietals and occipital are practically one continuous bone due to the ossification of the sutures between them ; the basilar process is continuous with the body of the sphenoid and the lesser wings of the sphenoid are continuous with the orbital plates of the frontal. The lambdoid suture meets the sagittal suture at a point about two and a half inches above the inion. The center of the anterior fontanelle (the bregma) is at a point about one-fourth inch anterior to a vertical line connecting the external auditory meati. The intersutural fibrous tissue acts as a linear shock absorber which interrupts or reduces vibrations passing from one cranial bone to another. The bones of the skull are composed of two layers of compact tissue between which is interposed a layer of cancellous tissue known as the diploe or diploic layer. The outer layer is heavier, stronger and less brittle than the inner. The skull is by no means of a uniform thickness throughout, which fact may be nicely demonstrated by holding the base of the skull up against the light and noting the places which are translucent and those which are opaque. The thin regions are produced, to some extent, by obliteration of the diploe, and these areas of thinness and thickness are of importance in trephining and in estimating the probability of penetration in a given region. The thin places in the skull are the orbital plates of the frontal (supporting the frontal lobes), the squamous portions of the temporals (in contact with the spheno-temporal lobes) and the middle of the posterior fossa below the grooves for the lateral sinuses (which accommodate the cerebellum). At any of these places a well directed blow with a pen-knife could penetrate the skull and injure the brain. In contrast with the regions of thinness there are ridges which act as buttresses and serve to strengthen the skull. In the vault, they are situated as follows: the torus transversus occipitalis, a thickening in the bone extending laterally from the external occipital protuberance, a median thickening of the skull extending from the glabella to the foramen magnum and corresponding to the course of the superior longitudinal and occipital sinus, and the temporal crests ascending from the external angular processes of the frontal to be continued into the temporal ridges. In the base we have the ridges which divide the region into the three fossae and notwithstanding the fact that they are composed largely of thin, brittle compact tissue, they serve nevertheless to reenforce this part of the skull. They are : the petrous portion of the temporal and the lesser wing of the sphenoid. The base of the petrous portion of the temporal is applied to the skull in a region which corresponds to the mastoid externally and accordingly this part is comparatively strong. The foramen magnum is also surrounded by a ridge which is a bifurcation of the internal occipital crest, the two divisions ascending anteriorly to the posterior clinoid processes. These thickenings in the skull all have more or less tendency to modify vibrations and hence, to stop or divert lines of fracture. The foramina in the base of the skull are said to weaken it, and are of importance since the study of their positions and contents will aid in determining the location of the fracture. In the anterior fossa we have the cribriform plate of the ethmoid, the thinnest and weakest place in the floor of this fossa. It transmits the olfactory and nasal nerves, the latter passing through the nasal slit. In the middle fossa we have the sphenoidal fissure which transmits the nerves and vessels passing to the orbit : The motor occuli, abducens, patheticus, the three branches (nasal, lachrymal and frontal) of the ophthalmic and sympathetic nerves as they pass from the walls of the cavernous sinus to the orbit. These nerves are accompanied by three vessels: The orbital branch of the middle meningeal artery, a recurrent branch of the lachrymal artery and the ophthalmic vein. The foramen rotundum and ovale in the same fossa transmit respectively the second and third branches of the fifth cranial nerve together with other structures of minor importance. The middle meningeal artery enters the skull through the foramen spinosum situated in the tip of the great wing of the sphenoid. Through the carotid canal we have the internal carotid artery entering the cranial cavity accompanied by the carotid plexus of the sympathetic, the latter being continued into the cavernous plexus when it reaches the side of the body of the sphenoid. The foramina in the posterior fossa are the foramen lacerum posterius or jugular foramen, the internal auditory meatus, the two condyloid foramina and the foramen magnum. The jugular foramen transmits the glosso-pharyngeal, pneu-mogastric, and spinal-accessory nerves; also the lateral and inferior petrosal sinuses and a small artery. The inferior petrosal and lateral sinuses join to form the internal jugular vein a short distance outside the skull. The anterior condyloid foramen transmits the twelfth cranial nerve and occasionally an artery, the posterior condyloid foramen transmits a vein which establishes communication between the lateral sinus and the deep veins of the neck. The internal auditory meatus transmits the facial, the auditory and the pars intermedia of Wrisberg, also a branch from the basilar artery. The gustatory fibres of the seventh join the nerve as it enters the internal auditory canal and leave it by way of the chora tympani. Membranes of the Brain. — The brain as it lies within the skull is enclosed within three membranes which conform more or less closely to its surface. The dura, the most superficial of the three, is composed of tough inelastic tissue which acts as the internal periosteum of the skull and is richly supplied with blood vessels. Most of the nutrition of the bones of the skull is derived from vessels running in this membrane. The dura is composed of two layers, a superficial and a deep. The superficial, or vascular, layer acts as the endosteum while the deep layer is lined with endothelium on its deep surface, and dips down between certain portions of the brain to form partitions and give support. The dura as a whole is more firmly adherent to the skull in childhood and in old age than it is in middle life ; it is more firmly adherent at the base and where it crosses the sutures than elsewhere. Sir Chas. Bell has demonstrated the possibility of separating the dura from the bone without opening the skull; 'Strike the skull of a subject with a heavy mallet; on dissecting you find the dura mater to be shaken from the skull at the point struck. Kepeat the experiment on another subject and inject the head minutely with size injection, and you will find a clot of injection lying betwixt the skull and the dura mater at the part struck, and having an exact resemblance to the coagulum found after violent blows on the head.' The reduplications of the dura extending into the cranial cavity between the main portions of the brain are three in number; between the hemispheres of the cerebrum we have the falx cerebri, between the lobes of the cerebellum we have the falx cerebelli, and between the cerebellum and the occipital lobes of the cerebrum we have the tentorium cerebelli. The venous sinuses run between the layers of the dura which go to make up these three infoldings. The tentorium, like other portions of the dura, is a tough, inelastic membrane and, — since its crescentic margin is firmly attached to the grooves on the occipital bone (the upper edge of the petrous portions of the temporal bones and the posterior clinoid processes), — it is more or less liable to be torn when the cranium changes form during the process of moulding, as it passes through the birth canal. Intracranial hemorrhage may then take place from the sinuses running between its layers. The falx cerebri serves to prevent the hemispheres of the cerebrum from jostling each other when the head is struck or moved quickly, and the falx cerebelli serves the same purpose for the two halves of the cerebellum. The tentorium cerebelli sustains the weight of the occipital lobes and prevents them from pressing on the cerebellum. The pia mater is a delicate membrane which invests the surface of the brain, contains numerous small vessels which extend perpendicularly into the substance of the cortex. This membrane dips down into all the sulci, following the surface of the brain in every detail. It also forms the velum interpositum and the choroid plexus. The arachnoid lies between the dura and the pia, is composed of a loose areolar tissue and divides the space between the dura and pia into the subdural and the subarachnoid spaces. The arachnoid dips into some of the larger sulci, but resembles the dura in this respect more than the pia. The thickness of the membrane varies considerably in different portions of the brain. On the cerebral hemispheres it is thin and delicate, while the part investing the pons is heavy and much less vascular. The subarachnoid space (between the arachnoid and pia) is quite large at the base of the brain and is filled with cerebrospinal fluid. The subarachnoid and subdural spaces connect with the ventricular cavities of the brain through the foramen of Majendie in the posterior medullary velum of the fourth ventricle. The cerebrospinal fluid by its escape into the spinal spaces allows a certain amount of displacement of the cranial content. Vessels of the Membranes. — The vessels running in the dura are often partially accommodated by grooves on the inner surface of the skull, and this intimate contact between bone and vessel renders the latter quite liable to injury when the line of fracture traverses these bony channels. The 'most important artery in the dura is the middle meningeal, a branch of the first portion of the internal maxillary artery; it gains entrance to the skull through the fora- men spinosum and passes outward onto the internal surface of the squamous portion of the temporal, where it divides into an anterior and posterior branch. The anterior branch passes outward and forward, while the course of the posterior branch is outward and backward. Both branches are continued onto the inner surface of the parietal bone. There is considerable normal variation in the courses of these two branches after they reach the parietal bone, and we have no possible means of ascertaining the exact position that they may occupy in a given case. The anterior branch, however, will usually be found passing upward and slightly backward from a point about one and three quarters inches above the zygoma and one and a half inches behind the external angular process of the frontal bone. The course of the artery <Callout type="tip" title="Tip">Fig. 515. — Internal surface of right half of skull showing courses of middle meningeal artery and lateral sinus. In this case the posterior branch of the artery is double and calls attention to the frequency with which anomalies occur in the course and distribution of this vessel.</Callout> is nearly parallel to the coronal suture, running from one-half to three quarters of an inch behind it. A trephine opening with its center about one inch above the external auditory meatus will expose the posterior branch of the middle meningeal. In trephining in this region it should be remembered that the skull is thin, the internal surface irregular and that the anterior branch of the middle meningeal (especially in the region of the pterion) may run in a complete bony canal instead of a groove. Kronlein's diagram gives the three most frequent sites for the location of clots following hemorrhage from this artery. The diagnosis of the position of these clots is often difficult, sometimes impossible. <Callout type="warning" title="Warning">The 398 FRACTURES AND DISLOCATIONS most satisfactory method has been found in the osteo-plastic flap which exposes enough of the brain to satisfactorily explore its surface without missing the site of hemorrhage.</Callout> Meningeal hemor- rhage may take place from some of the smaller meningeal arteries and occupy regions in the frontal or occipital lobes. A common form of meningeal hemorrhage is that arising from small veins. A linear fracture may divide small veins, and the resulting hemor- <Callout type="risk" title="Risk">rhage, though slow, not infrequently forms a large coagulum. In this form of hemorrhage the symptoms are slow in developing because it takes a number of hours for the clot to assume sufficient size to cause disturbance.</Callout> In addition to the middle meningeal artery, there are also other meningeal arteries of smaller size. They are the three meningeals from the ascending pharyngeal : — the anterior meningeal from the internal carotid, the posterior from the vertebral, and the small meningeal from the internal maxillary. These arteries, however, are all of small
Key Takeaways
- Fractures of the skull can be divided into three groups: those that recover without treatment, immediately fatal cases, and those whose lives can be saved with proper treatment.
- Careful observation is crucial for accurate diagnosis in head injuries due to the unpredictability of symptoms.
- The anatomy of the skull and brain is essential for interpreting symptoms and administering appropriate treatment.
Practical Tips
- Always prioritize careful observation when diagnosing head injuries, as unexpected outcomes are common.
- Be aware that the middle meningeal artery can have variable courses, so be prepared to adapt your approach during surgery.
- Use an osteo-plastic flap method for exploring brain surfaces to avoid missing sites of hemorrhage.
Warnings & Risks
- Be cautious when dealing with linear fractures as they may divide small veins and cause delayed but significant bleeding.
- Understand that the unexpected is common in head injuries, so be prepared for variable outcomes.
- Recognize that the anatomy of the skull can vary significantly, especially in regions like the pterion.
Modern Application
While the techniques described in this chapter are rooted in historical practices, the principles of careful observation and accurate diagnosis remain crucial. Modern medical imaging has greatly improved our ability to assess head injuries, but understanding the anatomy and potential complications still provides valuable context for emergency response and treatment.
Frequently Asked Questions
Q: What are the three groups of skull fractures mentioned in this chapter?
The three groups are: those that recover without treatment, immediately fatal cases, and those whose lives can be saved or serious sequelae may be averted with proper treatment.
Q: Why is careful observation important when diagnosing head injuries according to the chapter?
Careful observation is crucial because unexpected outcomes are common in head injuries. The symptoms may not accurately reflect the severity of the injury, making it difficult to predict the patient's prognosis.
Q: What are some key anatomical features of the skull that should be considered when treating a fracture?
Key anatomical features include the thin regions such as the orbital plates of the frontal bone and the squamous portions of the temporals, which can be vulnerable to penetration. Additionally, ridges in the skull act as buttresses and serve to strengthen it.