Serous meningitis, no doubt very rarely occurs as a primary disease in a previously healthy child; usually it appear.s as a complication in the course of various infections. In infants pneumonia and gastro enteritis; in older children, whooping-cough, measles and purulent otitis media are most frequently the primary diseases.
Pneumo- and streptococci and bacterium coli seem to be the com monest infectious agents; but besides these typhoid bacilli, staphy lococci, and influenza bacilli have been found. It is noteworthy that only small numbers of all these microorganisms are contained in the spinal fluid of serous meningitis; while in the purulent forms large numbers are easily found. According to the anatomic localization of the inflammatory process it is possible to distinguish an acute external and internal serous meningitis but of course they may appear together.
The niacroscopical pathology in the external form consists chiefly' in ffidema of the leptomeninges which in its scope may involve both base and convexity or be confined to islands in single larger or smaller areas. The differentiation from congestion ffiderna of the pia is only possible by microscopic evidence of inflammatory infiltration of the meninges, particularly of the lymphatics of the small vessels of the pia and cortex. Concerning this numerous investigations have been pub lished during the last twenty years.
In the internal form we find dilatation of the ventricles and flatten ing of the convolutions: the fluid is usually clear, with slight changes which indicate inflammation of the ehorioid plexus or ependyma.
In acute eases hydrocephalus never attains very extensive devel opment: when this exists moreover, it implies a ehronie, perhaps a chronic intermittent disease, to the consideration of which we shall return.
The clinical picture of serous meningitis exhibits various types and courses within the limits of the meningeal conditions.
A fulminating form, " apoplexia serosa '' of the older authors, is exhibited in infants by convulsions beginning suddenly with high fever, sometimes hyperpyrexia and eoma.
Apart from slight cervical rigidity, which moreover is not always present, and contracted pupils, nothing points to meningitis. Death occurs within a few hours or day. Finkelstein has, published some very
instructive observations of this intricate condition which were (geared up by the autopsy.
At the same time he lays stress upon the fact, in which we thoroughly agree with him, that in such cases the severe convulsions do not depend upon a particularly virulent infection, but upon an abnormally violent reaction of the affected children, who invariably have given evidence of the spasmophile diathesis before this disease.
In less frequent, favorable cases the turbulent onset is succeeded by a clinical picture, which displays pronounced meningeal features and, as Finkelstein says, depends chiefly upon the external form of serous meningitis. Much more frequently this type does not begin so abruptly, but more gradually.
Ventricular serous meningitis, the so-called acute hydrocephalus of childhood, has been reeognized much long,er and is better understood.
"From the external form it is clinically distinguished by the accent uation of pressure symptoms. For practical purposes it may be grouped into two divisions, viz.: cases with acute onset and in which convulsions predominate and cases with insidious development in which coma pre dominates" (Finkelstein).
The convulsions, which usually occur during the course of a more or les.s severe infectious ga.stro-enteritis attended by fever, differ from simple eclamptic convulsions primarily in their longer duration.
While eclamptic attacks continue scarcely longer than a few min utes, and in the status eclampticus recur repeatedly at short intervals, the convulsions due to serous meningitis may last for hours or days with only isolated interruptions, exactly as is the rule in other organic cerebral affections. Clinically, the convulsions resemble those caused by auto intoxication, circulatory or metabolic disturbances of early childhood, which Thiemich has described as terminal.
A further important differential point between functional con vulsions of pyretic origin and those due to meningitis is the possibility of observing at least to some extent cervical and spinal rigidity, hyper tony, contracted pupils, somnolence, etc., during the variable intermis sions between and at the conclusion of conYulsions.