This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Fractures by counter stroke are now regarded as of much less frequent occurrence than formerly. Charles Phelps found in 147 cases of fracture of the base of the skull 12 which had not extended from the vault. In these, the force had been applied to the parietal region in six, and in five to the occiput; most of the resulting fractures were in the region of the orbit. Only two of the twelve cases were serious fractures, the remaining ten being slight fissures, which produced no symptoms.
Fig. 22. - Interior view of the base of the skull, showing the parts most liable to be involved in fractures.
Hemorrhage is a frequent and most valuable symptom in diagnosing the existence of fracture and in determining its location.
A fracture through the roof of the orbit causes bleeding into the orbital cavity; the blood works its way forward and makes its appearance under the conjunctiva of the ball of the eye. Its progress forward toward the lids is blocked by the orbitotarsal ligaments, and it therefore works its way downward to the bulbar conjunctiva, under which it advances to the edge of the cornea. The ordinary ecchymosis of the lids and cellular tissue around the eye is usually due to a rupture of the vessels of the subcutaneous tissue by a blow from the outside, and not to a fracture of the base of the skull.
Fracture through the middle cerebral fossa may pass through the body of the sphenoid or basilar process of the occipital bone and cause bleeding into the mouth. It may also cause an accumulation of blood behind the posterior wall of the pharynx, pushing it forward. When it passes through the petrous portion of the temporal bone, as is frequently the case, it may involve the external auditory meatus and bleeding from the ear will result.
Fig. 23. - Middle and posterior meningeal arteries supplying the interior of the skull.
Bleeding from the middle meningeal artery, epi- or extradural hemorrhage, occurs in those fractures which pass through the region of the pterion. This point is the junction of the coronal and sphenoparietal sutures, about 4 cm. (1 1/2 in.) behind and slightly above the external angular process of the frontal bone. The middle meningeal artery comes up through the foramen spinosum and then goes forward, upward, and outward to the lower anterior angle of the 2 parietal bone. It sends branches forward to the frontal region and backward to the parietal and temporal regions. During two to three centimetres of its course, at the pterion, it passes entirely through bone, and therefore if a fracture occurs at this point it must of necessity tear the artery. The posterior branches are not regular in their course, one passing backward, low down, parallel to the zygoma, and another higher up in the direction of the parietal eminence. The branches of the meningeal artery nourish the bone as well as the dura, therefore if the dura is loosened from the bone hemorrhage from these branches occurs. The most frequent site of middle meningeal hemorrhage is in the region of the pterion or temple.
Fig. 24. - Points of trephining for hemorrhage from the middle meningeal artery. The course of the artery' has been marked on the outer surface of the skull.
In trephining for it, the centre of the trephine is to be placed on an average of 4 cm. (1 1/2 in.) behind the external angular process of the frontal bone, and on a level with the upper edge of the orbit or 4.5 cm. (1 3/4 in.) above the zygoma. If the artery is not sufficiently exposed more bone is to be removed by the rongeur forceps. It is in this region that epidural hemorrhages are apt to be extensive, because the vessels torn are the largest; but epidural hemorrhage can also occur in the frontal region from the anterior branches and in the parietal from the posterior.
Fig. 25. - Exit of cranial nerves at the base of the skull.
Trephining for bleeding from the posterior branch of the middle meningeal artery is somewhat uncertain. In some cases the artery runs low down, about 2 cm. (4/5 in.) above the zygoma and parallel to it. In other cases it runs upward and backward toward the parietal eminence. The trephine may be placed as high up as for the anterior branch of the middle meningeal artery, 4.5 cm. (1 3/4 in.), and 5 cm. (2 in.) farther back. This will be below and anterior to the parietal eminence and about midway on a line joining the parietal eminence and external auditory meatus. After the button of bone has been removed, additional bone may be cut away with the rongeur forceps until access can be had to the bleeding point (see page 23 for a case of rupture without fracture).
Rupture of the large venous sinuses and of the small vessels passing between the bone and dura also contribute to the formation of the clot. Owing to the firmer attachment of the dura mater in children, the meningeal arteries are more liable to be torn and cause hemorrhage than is the case in adults. For the same reason the blood pressure is not sufficient to dissect the dura from the skull, therefore epidural clots are rare. If there is a fracture, blood may collect beneath the scalp, and if an external wound exists, the blood will find an exit through it.