CONGESTION OF THE BRAIN.
of the brain is a term which is often used very loosely, and is probably applied to forms of illness. Writers who have dealt with the subject of disease in early life differ curiously in the importance they attach to the subject of cerebral hyperaemia, some attributing to it most of the convulsive diseases to which young children are liable ; others, as Valleix, asserting that this pathological condition is almost unknown in infancy.
The view formerly held that the quantity of blood circulating within the cranium is constant and cannot be influenced by altered conditions of the body generally, has now been proved to be erroneous. The researches of Robin and of His have shown that surrounding the cerebral blood-ves sels are lymphatic sheaths which communicate with the lymphatics of the pia mater, and are several times the size of the blood-vessels they enclose. 'These lymphatic canals contain a fluid which increases or diminishes in quantity according to the varying distention of the blood-vessels, and must therefore allow of great variety in the amount of fluid circulating within the cranial cavity. There is no doubt, therefore, that hyperaemia of the blood-vessels can take place ; but it does not follow because evi dences of this congestion are discovered in the dead body that it was the cause of.the symptoms from which the patient had suffered. It is common in cases of death from convulsions to find engorgement of the vessels of the brain and membranes, but this engorgement is probably as often a consequence of the convulsion as a cause of it. Still, every physician practising amongst children must now and again meet with cases in which he finds a group of symptoms suggestive of some temporary increase of pressure upon the brain. These symptoms either pass off after a time and the child recovers, or they increase, the patient dies, and on examination of the skull cavity nothing but a hyperaemic state of the cerebral vessels with an effusion of serum is seen to account for the illness. These symp
toms are therefore supposed to indicate congestion of the brain ; but there is probably some deeper and less obvious cause of the impairment of function, for although this pathological condition may be invariably pres ent, it cannot be held to furnish a full and satisfactory explanation of the phenomena.
Causation.—Ceiebral congestion may occur in two forms : An active hyperaemia from increased flow of blood into the brain, and a passive hy peraemia from obstruction to the return of blood from the interior of the skull. Many different causes have been enumerated as giving rise to the condition, but it is difficult to accept all of them as determining agents in the production of cerebral congestion. Dentition is usually said to be a cause of vascular engorgement, because the teething process is often ac companied by convulsive seizures ; but in these cases, if cerebral hyperce mia occur, it is as likely that the convulsive seizures are the cause of the congestion as that the congestion determines the fits. The intense con gestion of the face, and the swelling of the veins of the neck, which are always present in a convulsive fit, show that there is impediment to the return of blood from the head ; at the same time the heart's action is ex cited, and blood is being propelled rapidly into the cranium. There must be therefore great engorgement of the vessels in this region, and if the fits are frequently repeated and the child remains for hours, as often hap pens, in a more or less convulsed state, the engorged vessels must relieve themselves by effusion of serum, and perhaps by minute hemorrhages. Pressure upon the brain set up by this means is sufficient to account for the stupor, squinting, etc., which are often found to follow a convulsive seizure ; but the effusions. are in all probability like the venous congestion itself, a consequence rather than a cause of the nervous commotion.