VASCULAR DISEASES OF THE BRAIN. — The subjects of CEREBRAL ILEMORRHAGE, ENCEPHALITIS, CERE BRAL ABSCESS, and HYDROCEPHALUS have been already treated, and hence need no further mention.
Cerebral vascular diseases might be considered as to their effects: 1. On the permeability of the vessel-walls. 2. On the vasomotor arrangements for the brain itself. 3. On the brain-tissue involved by vascular obstruction.
The main facts so far known regarding the vascular pathology of the brain hinge on the last one of these points. Hence the best basis for approaching this sub ject is an outline of the effects produced by blocking of each individual vessel or branch. The causes and consequences will then admit of a more concise and satisfactory handling.
In general, it may be said that the ef fects are somewhat proportional to the size of the vessel and the suddenness with which the block occurs. Of course, as regards the eventual amount of anatom ieal damage suddenness has little to do.
The anatomy and nomenclature given in the writer's article on "Vessels of the Brain" in volume viii of the "Reference Hand-book of the Medical Sciences" will here be followed.
General Symptomatology.
—(a) The Dural Arteries. —For two reasons, obstruction in these is harmless. In the first place, they do not have to do with the brain proper, but constitute in this particular an in dependent system. In the second, they are not terminal vessels, but are at all points protected by ample anastomoses.
(b) The Brain-arteries P ro per.—The main factor here is the fact that, aside from the chief trunks, all the distribut ing vessels are more or less terminal arteries, and in part strictly so. Conse quently the area supplied by any one of them is, in case of closure (embolism, thrombosis, obliterating arteritis, or en during [?] functional spasm), bound to undergo softening to a corresponding extent—the whole area, if a strictly terminal vessel, and a portion if only partially so.
The true terminal arteries are the perforants at the base and the small branches from the basilar directly enter ing the pons. But beyond the circle of Willis, all the pial arteries of much size are partially terminal.