The Surgery of the Skull and Brain

by Louis Bathe Rawling

The alternative theory states that the old tissue destruction and the new tissue formation sets free certain toxic substances which act on the optic nerve-fibres, leading to œdema and inflammation. Paton, however, comes to the conclusion that ‘the nature of the tumour does not play any part in determining the onset of neuritis except in so far as the nature determines its localization’.

Whatever be the localizing value of optic neuritis, it is generally accepted that it commences in the upper nasal quadrant.

Visual acuity is but little impaired in the earlier stages of optic neuritis, but so soon as atrophic changes develop, diminution in the field of vision occurs.

The pupillary changes associated with tumours of the brain are closely connected with these fundus changes. In the early stages, the pupils may be contracted with the object of protecting the inflamed surfaces exposed to light, whilst, when atrophy develops, the pupils may steadily dilate, becoming fully dilated and fixed as the atrophic changes become fully developed.

These pupil changes must therefore be taken into consideration in estimating the value of pupillary changes in general.

Vomiting.

Vomiting is dependent on stimulation of the medullary vomiting centre, or on irritation of the dura mater in the immediate neighbourhood of the tumour. The dura is supplied by branches of the fifth cranial nerve, the stimulus being referred to the vagus centre in the floor of the fourth ventricle.

Vomiting is of the so-called ‘cerebral’ type. It is of frequent occurrence, generally irrespective of ingestion of food and seldom preceded by any nausea and retching. The attacks are often associated with exacerbation of headache, and more rarely with some slight elevation of temperature. The more severe the vomiting the more likely is the tumour to be subtentorial in position.

Alterations in pulse, respiration, and blood-pressure.

In the early stages there is but little alteration in pulse and respiration. Later on, the increasing intracranial pressure acts as a stimulus on the vagus and vaso-motor centres, the pulse becomes slowed and the blood-pressure raised. When the pressure is considerable, the slow pulse and deep, even stertorous, respiration evidence the effect produced on the medullary centres. In the terminal stages the imminent exhaustion of these centres is heralded by progressive acceleration of the pulse, by great fall in blood-pressure, and by the advent of Cheyne-Stokes respiration.