Diseases of the blood-vessels are among the most frequent causes of gross brain disease. Arteries or veins—more frequently the former—may become blocked or ruptured from various causes. The immediate effect is a disturbance or loss of conscious ness, and the individual may be "struck down" (see APOPLEXY) and never regain consciousness (see COMA). Should conscious ness return, more or less permanent loss or disturbance of func tion becomes obvious. Paralysis of some form, especially hemi plegia, is commonest.
The cerebral arteries, usually the left middle cerebral may be occluded by embolism (q.v.). The area of brain supplied by that artery undergoes softening in consequence, resulting in paralysis of the opposite half of the body (hemiplegia) associated with aphasia when the paralysis affects the right side in a right-handed person (see Plate, fig. I). When the embolus is infective, as in ulcerative endocarditis, it not only blocks the vessel but leads to an infective inflammation and softening of its coats, with the formation of an aneurism. The aneurism may suddenly rupture into the substance of the brain and produce apoplexy. Most cases of apoplexy from cerebral haemorrhage in young people are due to this cause. Softening may also arise from coagulation of the blood (thrombosis) in the arteries or veins. Many causes gener ally combine to produce thrombosis, viz., a weak acting heart and altered conditions of the blood. It is sometimes met with in the cachexia of phthisis and cancer, in typhus and pneumonia, after parturition and in marasmus at all periods of life, but especially in the very young and very old. But thickening, roughening, and a degenerated condition of the cerebral arteries known as atheroma, when associated with a weak acting heart is especially liable to give rise to thrombosis and softening, and is a very common cause of apoplexy, paralysis and mental deterioration in people who have passed middle life. General disease of the arteries of the body, with chronic Bright's disease and high arterial pressure, is frequently associated with the formation of minute aneurisms upon the cerebral arteries, which may rupture and cause apoplexy. This is especially liable to occur in a vessel supplying the basal ganglia, the effused blood tearing through the motor efferent fibres (pyramidal tracts) lying between the optic thalamus and the corpus striatum (see Plate, fig. 3). The result is hemiplegia of the opposite side of the body. Disease of the arteries of the central nervous system, occurring in a person under 4o, is generally due to syphilis, the virus of which produces an inflammation of the inner coats (see ARTERIES, DISEASES oF). The thickening and nar rowing of the lumen with loss of elasticity of the arteries of the brain generally may suddenly or gradually set up cerebral anaemia and give rise to semi-comatose and comatose or even apoplectic states. Occlusion by the inflammatory proliferation or by the sud
den clotting of blood in the diseased vessel may occur, the immedi ate effect of which may be an epileptic or apoplectic fit ; the result is softening; and as any or all of the arteries of the brain may be affected successively, simultaneously, or at random, the symptoms may be manifold. They may be general or local, and are often as sociated with inflammation of the membranes. The disease, under treatment, may abate, and the paralytic or mental phenomena partially or completely disappear, indicating the restoration, or partial restoration, of the circulation in the diseased arteries; sometimes with the lapse of treatment, and sometimes without, new symptoms manifest themselves, showing that the disease has attacked a fresh set of arteries. Disseminated sclerosis (in sular) is another progressive random, morbid process, the pathol ogy of which is not fully understood, but is probably due to some toxic cause. Islands of nervous tissue undergo a morbid change, commencing in the myelin sheath and ending in an increase of the supporting neuroglia tissue at the expense of the true nervous tissue (see Plate, fig. I I).
Tumours and new growths in the central and peripheral ner vous systems may be primary or secondary; the former arise in the supporting, enclosing or nutrient tissue elements; the latter are metastatic deposits from tumours originating elsewhere. Tu mours may be single or multiple, the special symptoms occasioned depending upon the seat of the tumour and whether it destroys or only irritates the adjacent nervous tissue. Tumours situated within the cranial cavity cause general symptoms, namely, optic neuritis, severe headache and vomiting; these symptoms, which are caused by increased intracranial pressure, are more severe in rapidly growing vascular tumours, even though small, than in large slow-growing tumours. Some tumours are highly vascular and a large thin-walled vessel may suddenly rupture and cause an apoplectic fit. If the growth is situated in a portion of the cortex having some special localizing function, e.g., the motor area, it is likely to give rise to epileptiform convulsions, starting in a limb or definite group of muscles ; but the irritation usually spreads to the whole motor area of the same side, and even extends to the opposite hemisphere, by an overflow of the dis charge through the corpus callosum. In such case there is loss of consciousness. If, however, the tumour destroys the cerebral cortex of a particular region, it may give rise to a paralytic lesion, e.g., paralysis of the arm.