Whatever the nature of the osseous lesion, the mortality is almost entirely dependent on the question of associated injury to the intracranial contents, more especially the brain.
In the case of fractures purely or mainly basic, of the cases that have come under my care or observation, 116 recovered and 89 died--a mortality of 44 per cent.
Battle, from an examination of 168 cases, puts the mortality at the low figure of 32 per cent., whilst Crandon and Wilson, from an exhaustive series of 530 cases, estimates it at 44 per cent.
The mortality varies according to the _age_ of the patient, the death-rate being at its maximum at the two extremes of life--between 50 and 60 per cent. under the age of 5 years and over 60 per cent. after the age of 70.
The mortality varies also according to the _fossa_ implicated. Thus, to each fossa there are certain peculiar dangers--to the _anterior_ fossa, meningeal infection from the nose, frontal and ethmoidal sinuses; to the _middle_ fossa, meningeal infection from the naso-pharynx and ear, and hæmorrhage from the middle meningeal and internal carotid arteries, and from the cavernous venous sinus; and to the _posterior_ fossa, laceration of the lateral and sigmoid venous sinuses.
After such consideration of local complications, it would appear that the middle fossa of the skull presents the greatest dangers. Another factor must, however, be taken into consideration--injury to the brain--the commonest cause of death in all head injuries. The main vital centres are grouped in the region of the fourth ventricle, and Leonard Hill has proved that any increase in the intracranial pressure exerts its influence most rapidly and most effectually when the lesion is situated beneath the tentorium cerebelli.
One may assume, therefore, that fractures of the posterior fossa are the most dangerous, and that those involving the anterior fossa hold out the best prognosis.
In the case of pure or primary vault fractures the mortality may be estimated by reference to the following table. It is composed from 88 cases admitted into St. Bartholomew’s Hospital between the years 1900 and 1906.
Under the age of 5 8 lived and 2 died. Mortality, 20 per cent. „ „ 10 2 „ „ 3 „ „ 60 „ „ „ 15 6 „ „ 0 „ „ 0 „ „ „ 20 10 „ „ 3 „ „ 23 „ „ „ 30 9 „ „ 1 „ „ 10 „ „ „ 40 16 „ „ 9 „ „ 36 „ „ „ 50 3 „ „ 7 „ „ 70 „ „ „ 60 2 „ „ 1 „ „ 33 „ Over the age of 60 3 „ „ 3 „ „ 50 „