This form of hydrocephalus is one of an eminently chronic character; it exists at birth, and usually has then already made considerable progress; but, if not, it soon increases, and, by the extraordinary size which it attains, and the amount of deformity it produces, it constitutes the most striking example of the disease.

It is then distinguished by the large quantity of serum which the ventricles contain, and by the extent to which they and the skull are enlarged. Those cases in which no monstrosity of the brain coexists, may be portrayed as follows: The quantity of serum contained in the ventricles amounts to several pounds, 6-10, or even more: the ventricles are expanded into large elliptical cavities, or membranous sacs; and their ependyma or lining membrane is generally much thickened. The cerebral mass around the ventricles, especially towards the top of the head, is attenuated, and sometimes measures scarcely a line in thickness: it may be even so reduced as to be but a just perceptible layer covering the membrane. In one case, which is preserved in the Vienna Museum, it is broken quite through, at the upper part of the hemispheres, by the thickened membranous walls of the ventricles, and has receded from them to a considerable extent. Internally and inferiorly, the seum by its pressure flattens the corpora striata and optic thalami, and passing into the third ventricle, it forces those bodies asunder also; the corpora quadrigemina become smoothed, the commissures stretched, and the gray commissure very commonly wasted; the pillars of the fornix are forced apart, and, with the septum, driven up against the corpus collosum; they are also either all much raised, or the septum is enlarged, very much thinner than natural, and broken through in one or more places of various size. The floor of the third ventricle is thin and transparent, the cerebellum is flattened from above: the pons is flat and spread abroad; the crura cerebri are separated; the pituitary gland is flat, or even concave, and wasted from pressure. The size of the cerebrum is greatly disproportioned to that of the cerebellum, the parts at the base of the brain, and the nerves. The surface of the cerebrum is flat, its convolutions are but just indicated, and could not be recognized; and all the membranes of the brain are unusually delicate and thin. The head is quite remarkable for its size and its deformity. (Compare p. 168).

Congenital hydrocephalus is far from constantly agreeing with this picture: on the one hand, the quantity of serum, and the enlargement of the ventricles and skull, may be less than has been stated, and may indeed only just exceed the normal standard: while, on the other hand, under certain conditions, the development of the brain may be faulty, even to monstrosity.

The mode of origin, or pathogenesis, of congenital hydrocephalus differs most probably in no essential particular from that of the chronic hydrocephalus which commences in the extra-uterine periods of life. It may come on in the foetus as acute hydrocephalus, or appear originally in the chronic form. The general arrangement of the skull of the foetus, and the manner in which the cerebrum itself is developed, are both highly favorable to an excessive accumulation of serum. And I believe, that the really essential part of congenital hydrocephalus, that which arrests the development of the brain, is the affection of the ependyma; that, in proportion to the degree to which the hydrocephalus has advanced, and according to the period of foetal life at which it commenced, it does, in various manner, and to different extent, arrest the development of the brain, and occasion monstrosity of it; and so far contains the ground of its alliance with hemicephalus, hydrencephalocele, singleness of the cerebrum (cyclopia), etc.

What has been said of the combinations of acquired chronic hydrocephalus, describes those of the congenital disease also. A congenital dwarfish growth sometimes takes the place of rickets.

Terminations

The hydrocephalus of the foetus, even when it has reached a considerable extent, is not unfrequently inherited by the child, the youth, and even the adult. During the intervals in which the disease is quiescent, the brain grows, and acquires its normal volume, and the skull, continually advancing over it, at length closes. In some rare cases, growth passes beyond its normal bounds into hypertrophy; but with regard to the cure of hydrocephalus by hypertrophy, what has been said at p. 273, may be applied in this place.

The disease sometimes proves fatal by the pressure which the continual accumulation of water exerts upon the brain. Frequently, too, acute inflammation of the ependyma, and meningitis arise in its course. I have, moreover, seen it terminate by rupture of the brain and dura mater, and extravasation of the serum of the ventricle beneath the pericranium and adjoining aponeurosis.

Finally, considerable importance attaches to the hemorrhages which take place in the course of the disease: they are met with both in the arachnoid sac and also, and more especially, in the dilated ventricle. They are remarkable for the length of time during which they are borne, as is attested by the metamorphoses of the extravasation. The way is most probably prepared for their occurrence by the stretching of the vessels of the membranes that cover the brain and line the ventricles, during the distension of the latter; and it is by the final rupture of those vessels that they are actually produced.